Institution of Highways and Transportation 1997 Transport in the Urban Environment. London CIHT

Guidelines for

THE ENVIRONMENTAL
MANAGEMENT OF HIGHWAYS

THE INSTITUTION OF HIGHWAYS & TRANSPORTATION

G UIDELINES

FOR

T HE E NVIRONMENTAL
M ANAGEMENT OF H IGHWAYS

Published By
T HE I NSTITUTION O F
H IGHWAYS & T RANSPORTATION
F EBRUARY 2001

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

1

T HE E NVIRONMENTAL
M ANAGEMENT OF H IGHWAYS
is sponsored by

The sponsors are listed above in alphabetical order. They are: Cleveland Potash Ltd; The Countryside Agency; English Heritage;
The Environment Agency; Highways Agency; Rees Jeffreys Road Fund; Roads Service Agency,
Department for Regional Development (NI), and Salt Union Ltd (The De–Icing Business).
2

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

G UIDELINES

FOR

T HE E NVIRONMENTAL
M ANAGEMENT OF H IGHWAYS
M ESSAGE F ROM A LAN C RAIG
IHT P RESIDENT 2000–2001

Transport touches all our lives. It affects not only commerce, recreation and the environment, but lifestyle as
a whole. While it brings great social and economic benefits, the highway system and its management also
affects the environment. Minimising the adverse environmental effects of transport must be a top priority for
policy makers and practitioners alike.
The Government’s recently published Transport 2010: The Ten Year Plan acknowledges the strong
economic, environmental and social case for investment in infrastructure in all modes of travel. It also
recognises that reducing the impact of transport on the environment, both locally and as part of wider
international efforts, is a central aim.
The Institution of Highways & Transportation is internationally acknowledged for its best practice
guidelines in the transportation field. The Guidelines on The Environmental Management of Highways
continue that tradition. It outlines the development of environmental policy in the UK and describes best
practice in a range of key environmental topics relating to transport.
Key issues covered include drainage and groundwater management; air quality and noise management;
landscape management; ecology, biodiversity and the management of highways within the context of the built
heritage. It also suggests a systematic approach to the environmental management of highways based on the
European Standard, ISO 14001, for Environmental Management Systems.
The aim of the Guidelines for The Environmental Management of Highways is to describe best practice
in managing and maintaining transport infrastructure, especially but not exclusively highways, in such a way
as to minimise potentially harmful environmental impacts and maximise environmental gains.
The emphasis is on planning, management, layout and engineering. Making the very best use of our
existing road network at least cost to the environment by knowing what to do and when and how to do it.
I would like to thank all those involved in the production of these Guidelines, particularly the Steering
Group members, the Managing Editor, authors, photographers and others who contributed material, those
who responded to the consultation, and the IHT staff. I must also particularly thank our sponsors.
On behalf of the Institution, I am pleased to commend The Environmental Management of Highways
to all with a professional interest in the future of our environment and the quality of the transport network.

President 2000–2001
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

3

4

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

C ONTENTS

PAGE N O

F ROM T HE M INISTER

I NSIDE F RONT C OVER

M ESSAGE F ROM T HE P RESIDENT
1. A BOUT

THE

G UIDELINES

2. P OLICY C ONTEXT
2.1

Introduction

3
11
15
15

2.2
The Four Ages of transport policy in Britain
2.2.1 New Realism, The Great Transport Debate and towards a Fifth Age of transport policy

15
15

2.3
Global and European policy
2.3.1 Global policy
2.3.2 European transport policy
2.3.3 The European Auto–Oil Programme

18
18
18
19

2.4
Current UK transport policy
2.4.1 The 1998 White Paper
2.4.2 The Daughter Documents
2.4.3 Related documents
2.4.4 Transport 2010: The 10 Year Plan

19
19
21
28
30

2.5

31

Other key legislation

2.6
Conclusions
2.6.1 The increasing influence of environmental issues
2.6.2 Some final conclusions
References

3. E NVIRONMENTAL M ANAGEMENT S YSTEMS

31
31
32
34

39

3.1

Environmental protection and management

39

3.2

Legislation and regulation

41

3.3

Organisational considerations

42

3.4

Key considerations

45

3.5

Delivering good environmental practice

46

3.6
The environmental management framework
3.6.1 Choosing a standard

48
50

3.7
The ISO 14001 Standard
3.7.1 Organisational evaluation standards
3.7.2 Product evaluation standards

52
52
53

3.8

55

Building an EMS

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

5

3.9
The highways environmental management model
3.9.1 Stage 1. Know the environmental risks
3.9.2 Stage 2. Manage the environmental risks
3.9.3 Stage 3. Learn and improve

58
59
61
63

3.10

64

Future trends

References

4. D RAINAGE , R UNOFF

65
AND

G ROUNDWATER

Introduction

67

4.2

Pollutant accumulation on highway surfaces

67

4.3
Classification of highway pollutant sources
4.3.1 Solids
4.3.2 Metals
4.3.3 Hydrocarbons
4.3.4 Inorganic salts, herbicides and bacteria

69
70
71
71
72

4.4
Sources of highway pollutants
4.4.1 Vehicle emissions, vehicle part wear and vehicle leakages
4.4.2 Road surface erosion
4.4.3 Accidental spillages
4.4.4 Atmospheric deposition
4.4.5 Seasonal maintenance practices
4.4.6 Regular maintenance practices

72
72
73
73
73
73
74

4.5
Legislation and responsibilities
4.5.1 Legislation and legal liability
4.5.2 Water quality objectives and standards
4.5.3 EU legislation
4.5.4 Groundwater regulations
4.5.5 Spillages and emergencies
4..5.6 Highway authorities

75
75
76
78
79
79
81

4.6
Treatment of highway runoff
4.6.1 Filter strips and swales
4.6.2 Filter drains
4.6.3 Infiltration systems
4.6.4 Storage facilities
4.6.5 Alternative road surfacings

82
82
83
85
87
91

4.7
Recommendations
4.7.1 Costings
4.7.2 Design selection
4.7.3 Specific recommendations

92
93
95
96

References

97

5. A IR Q UALITY M ANAGEMENT
5.1

Introduction

5.2
The problem of air quality
5.2.1 Historical perspectives
5.2.2 Current air quality

6

67

4.1

103
103
104
104
107

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

5.3

Current practice for impact assessment

115

5.4
Issues
5.4.1 Vehicle emissions
5.4.2 Atmospheric dispersion and transformation

117
118
123

5.5
Legislation and responsibilities
5.5.1 Vehilce and fuel standards
5.5.2 Air quality standards
5.5.3 International agreements
5.5.4 Local air quality management

125
126
129
129
129

5.6
Review and assessment of air pollution
5.6.1 Air pollution monitoring
5.6.2 Air pollution modelling

130
133
136

5.7
Control and reduction of traffic pollution
5.7.1 Traffic management
5.7.2 The impact of reduced emissions on air pollution levels

139
139
141

5.8
Practical measures to reduce traffic pollution
5.8.1 Emission reduction measures
5.8.2 Reducing the impact of the emissions

141
142
144

5.9

145

Principal recommendations

References

6. N OISE M ANAGEMENT

147

149

6.1
Introduction
6.1.1 The extent of the problem
6.1.2 Sources of road traffic noise
6.1.3 Trends in road traffic noise
6.1.4 Impact of road traffic noise

149
149
149
149
150

6.2
Measurement of road traffic noise
6.2.1 Definition of noise
6.2.2 Measuring noise
6.2.3 Sound levels and decibels
6.2.4 Frequency selectivity of human hearing and A–weighting
6.2.5 Temporal variation of noise and noise indices
6.2.6 Equivalent continuous sound level, L Aeq,T
6.2.7 Percentile exceeded sound level, L An,T
6.2.8 Temporal variations outside the noise index averaging periods, “T”
6.2.9 Efffect of microphone location relative to reflective surfaces

150
150
150
151
152
152
153
153
154
154

6.3
Calculation of road traffic noise and its radiation to the environment
6.3.1 Calculation of environmental road traffic noise

155
155

6.4
Human response to noise
6.4.1 Noise activity and interference
6.4.2 Noise annoyance
6.4.3 Noise and sleep disturbance
6.4.4 Noise and non–auditory health
6.4.5 Noise and community response

157
157
157
158
158
158

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

7

6.5
Planning Issues
6.5.1 Policy background
6.5.2 Planning Policy Guidance Note PPG24 – Planning and Noise
6.5.3 Land Compensation Act 1973
6.5.4 Noise Insulation Regulations 1975
6.5.5 Sound insulation and noise reduction for noise sensitive buildings
6.5.6 DoT Technical Memorandum – Calculation of Road Traffic Noise
6.5.7 DMRB, Volume 11 (3,7), Traffic Noise and Vibration

159
159
159
161
161
162
162
162

6.6
Guidance on best practice and noise mitigation measures
6.6.1 Land use and planning
6.6.2 Road surfaces
6.6.3 Noise barriers and landscaping
6.6.4 Traffic management
6.6.5 Cuttings, tunnels and enclosures
6.6.6 Building design and layout

163
163
163
166
169
169
170

6.7

171

Principal recommendations

References

172

7. L ANDSCAPE M ANAGEMENT

8

175

7.1

Introduction

175

7.2

Overview

176

7.3
Issues
7.3.1 Improvements
7.3.2 Day and night–time landscapes
7.3.3 Urban landscapes
7.3.4 Suburban landscapes
7.3.5 Rural landscapes

176
176
177
177
179
179

7.4
Guidance on best practice
7.4.1 Published information
7.4.2 Landscape design
7.4.3 Management plans
7.4.4 Management and maintenance contracts
7.4.5 Management operations
7.4.6 Mature trees and safety
7.4.7 Reinstatement after road works
7.4.8 Hard landscape and street furniture
7.4.9 Serendipity, sensitivity and selectivity
7.4.10 Nature conservation

181
181
182
183
184
185
187
188
188
188
189

7.5

190

Trends and future developments

7.6
Case studies
7.6.1 An urban road – the A316 in West London
7.6.2 A rural road – the A30 Okehampton Bypass, Devon
7.6.3 A suburban road – the A6141 in Letchworth Garden City, Hertfordshire
7.6.4 Lighting – A160/A180 Upgrade

191
191
191
192
194

7.7
Principal recommendations
7.7.1 Preventative measures
7.7.2 Palliative measures

194
194
195

References

195

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

8. T HE M ANAGEMENT

OF

E COLOGY

AND

B IODIVERSITY

197

8.1

Introduction

197

8.2

The importance of roadside areas for nature conservation

197

8.3

History of highway management and implications for wildlife value

197

8.4
Highway management and nature conservation
8.4.1 Conflict between highway safety and nature conservation
8.4.2 Conflict between nature conservation and uses of the verge
8.4.3 Responsibility for environmentally led highway management
8.4.4 Costs of highway maintenance
8.4.5 Conflicting needs of different species
8.4.6 Lack of research
8.4.7 Possible conflict with visual and landscape aspirations

199
199
199
199
200
200
200
200

8.5
Issues
8.5.1 Frequency and timing of cutting
8.5.2 Use of chemicals
8.5.3 De–icing compounds and other pollutants
8.5.4 Erosion and disturbance
8.5.5 Economic and practical considerations
8.5.6 Communication
8.5.7 Other, non–highway factors

201
201
202
202
204
204
205
205

8.6
Legislation and responsibilities
8.6.1 Statutory designations
8.6.2 Non–statutory designations
8.6.3 Protected species
8.6.4 Role of English Nature
8.6.5 Role of local authorities
8.6.6 Role of county wildlife trusts and other naturalists
8.6.7 Role of landowners

206
206
206
206
207
207
207
207

8.7
Guidance on best practice
8.7.1 Assessment of roadside areas
8.7.2 Cutting regimes
8.7.3 Use of chemicals
8.7.4 Erosion and disturbance
8.7.5 Tree planting and seeding
8.7.6 Definition of special verges
8.7.7 New roads/roadside areas

208
208
208
211
211
211
211
211

8.8
Case studies
8.8.1 Striped Lychnic moth in Buckinghamshire
8.8.2 Roadside reserves and nature wardens: Kent
8.8.3 Special verges in Essex

212
212
213
215

8.9

Where to find further information

216

8.10

Principal recommendations

216

References

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

217

9

9. M ANAGEMENT

H IGHWAYS

WITHIN THE

B UILT H ERITAGE

219

Introduction

219

9.2

Listed Buildings and Ancient Monuments

219

9.3
Groups of buildings
9.3.1 Settings of groups of buildings

220
220

9.4

Conservation and Conservation Areas

220

9.5

Spaces between buildings

221

9.6

Emphasis on linked spaces

222

9.7

Emphasis on the public street, road and highway

223

9.8
Why does heritage matter?
9.8.1 Cultural base of the community, national and local
9.8.2 Economic well–being
9.8.3 Contribution to regeneration

223
223
224
224

9.9

Emphasis on the whole scene

224

9.10

Heritage in everyday life

225

9.11 How can heritage be enhanced by highway management?
9.11.1 Enhance the setting
9.11.2 Reduce street clutter
9.11.3 Co–ordinate detailed design with the character of the locality

226
226
227
228

9.12 Challenges to the enhancement of heritage
9.12.1 Unresolved conflicting objectives and national advice
9.12.2 Limited interdisciplinary technical knowledge
9.12.3 Local decisions made incrementally and in isolation

229
229
230
231

9.13 Improving current practice
9.13.1 Materials
9.13.2 Signing and street furniture
9.13.3 Access
9.13.4 Lighting
9.13.5 Traffic calming

232
232
232
233
233
234

9.14 Examples of interdisciplinary considerations
9.14.1 Strand, London
9.14.2 Hennef, Germany

235
235
236

9.15

Repairs

237

9.16

Where to find further information

237

9.17

Principle recommendations

238

References

I NDEX

10

OF

9.1

238

243

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

C HAPTER 1. A BOUT THE G UIDELINES
The main purpose of these Guidelines for the Environmental Management of Highways is to
describe best practice in managing and maintaining transport infrastructure, especially
highways, in such a way as to minimise any potentially harmful environmental impacts and
maximise environmental gains. It is a technical document to support the aims of the 1998 White
Paper, A New Deal for Transport: Better for Everyone (DETR, 1998a), which viewed the
objective of environmental protection highly. Indeed the White Paper set the framework “to
minimise transport’s demand for land, protect habitats and maintain the variety of wildlife” and
to “limit the visual intrusion caused by transport”.
These Guidelines are intended for use mainly by planners, architects, highway engineers, traffic
engineers and maintenance engineers, in both the public and private sectors. As comprehensive
guidance on the environmental management of highways has been somewhat neglected in the
past, they highlight measures that can make qualitative improvements. They suggest techniques
for use and further development. The Guidelines are also intended to assist Councillors,
voluntary groups and others who wish to pursue improvements to the highway environment,
such as residents whose community is disrupted by heavy traffic. Finally, they are intended to
help promote a consensus amongst the authorities, professionals and user groups on the best
ways to improve conditions.

Scope and emphasis
The emphasis of these Guidelines is on what to do and how to do it. Those involved in the
planning and development process need to put a new emphasis on achieving good design.
Good urban and rural design, a concern for the overall quality of the environment and the built
environment in particular, is necessary for the creation of attractive living surroundings which
work well for everyone. The policy and planning framework is outlined, but the focus is on the
processes that will prevent or reduce environmental damage. Most examples are from the UK
but some examples from mainland Europe have also been included.
Where the term “highway” is used this should be taken to mean “road” in Scotland. Legislative
and administrative differences for Scotland, Wales and Northern Ireland are shown where
necessary. Furthermore, many of the lessons are also applicable to other transportation
infrastructure, such as railways and airports.

Relationship to other guidance
These Guidelines are intended to be compatible with other official guidance from The
Institution of Highways & Transportation (IHT), the Department of the Environment, Transport
and the Regions (DETR) and the Highways Agency (HA). To avoid repeating all that is contained
in comprehensive sources of nationally accepted guidance, such as Transport in the Urban
Environment (IHT, 1997) and DETR Local Transport Notes as well as the Design Manual for
Roads and Bridges (DMRB) , frequent reference is made to them. Such documents include, for
example, Places, Streets and Movements (DETR, 1998b) which sets out an approach that is
intended to prevent residential developments being dominated by roads and vehicles and
becoming standardised, regardless of their situation.
To achieve consistency in practice, local authorities are recommended to use these Guidelines
for the environmental management of highways (and other transportation infrastructure) by their
own staff, their consultants and developers, rather than producing a local guide.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

11

The Guidelines build on other advice that has been primarily intended for the construction of
new roads. It is recognised that there has been a major change in policy toward the transport
sector, the evolution of which is traced in Chapter Two. In very general terms the “predict and
provide” transport policies of previous generations have been replaced by an emphasis on
making the best use of what we have. In environmental terms, this means achieving best
practice in the maintenance, management and enhancement of the existing highway
environment: it is precisely here that these Guidelines are aimed.
It is important, however, that these Guidelines are not ignored for new highway provision where
appropriate. Pressure on scarce land resources in the UK means that a very substantial
proportion of new housing development will be on “brown–field” sites. Inevitably, this requires
that the associated new highway development (which includes, footways, cycle tracks and
reserved corridors for public service transport) integrate with existing provision.

Guidelines, not standards
The Guidelines attempt to set out best practice. It is recognised, however, that it will not always
be possible to meet all these criteria and that compromises must sometimes be made. The
Guidelines therefore try to indicate the desirable provision and lower standards that may prove
satisfactory in certain circumstances. They also suggest alternative approaches to tackling
problems. It is the task of the transport professional including planners, engineers and others to
decide if a lower standard is acceptable in given circumstances or if another approach would
be more beneficial.
The technical chapters of this publication all conclude with a number of “Principal
Recommendations”. It is accepted that, in virtually all cases, these recommendations have
resource implications that will have to be set alongside other competing demands on finite
budgets. The Guidelines attempt to prioritise these recommendations where possible, but it is
essential that all users of this document realise that their own professional judgement must be
exercised in the selection of appropriate procedures for local circumstances. It is important to
realise also that not all resources are directly financial, particularly where local volunteer
initiatives are available. In addition, it should be recognised that much of the management of
the natural and built environment is a matter of concern for all those with an interest in it, not
merely “professional” environmental scientists or engineers. Public/private partnerships and, for
example, town centre management partnerships now have a real role in setting priorities and
ensuring delivery of many of the recommendations contained in these Guidelines.

Guide to the Guidelines
The Guidelines are in two parts. Chapters two and three cover issues relating to policy and
management. Chapters four to nine deal with the technical details, providing advice on how to
avoid or mitigate harmful consequences of highways management and how to provide
environmental gain. Chapter two covers global and European policy including the European
Auto-Oil Programme. Current UK transport policy including the 1998 White Paper as well as
the “daughter” documents are also considered. Chapter three describes environmental
management systems so that environmental protection and management delivers good practice.
In addition to legislation and regulation, it also covers organisational considerations as well as
describing how to develop an environmental management strategy. Chapter four covers
drainage, runoff and groundwater management describing highway pollutant sources such as
vehicle emissions and vehicle component wear, vehicle leakage’s, road surface erosion and
accidental spillages. Chapter five addresses air quality management focussing upon vehicle
emissions. Chapter six is concerned with noise management, in addition to issues relating to the
calculation of road traffic noise. Landscape management is covered by Chapter seven. A
12

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

distinction is made between different types of landscape: day and night–time landscapes; urban
landscapes; suburban landscapes and rural landscapes. Chapter eight is concerned with the
ecological management of the roadside estate, and finally Chapter nine with the management
of highways within the built heritage.
The emphasis in these Guidelines is on planning, management, layout and engineering. Making
the very best use of our existing road network by knowing what to do and when and how to do it.

References
DETR, 1998a

A New Deal for Transport: Better for Everyone. Cmnd 3950.
The Stationery Office, London.

DETR, 1998b

Places, Streets and Movement , The Stationery Office, London.

The Institution of Highways &
Transportation, 1997

Transport in the Urban Environment. IHT, London.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

13

14

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

C HAPTER 2. P OLICY C ONTEXT
2.1 Introduction
The aim of this chapter is to provide the transport and environment policy context relevant to
the design, management and maintenance of highways. The chapter is structured as follows:
section 2.2 provides some historical context by identifying four ages of transport policy in
Britain. Section 2.3 highlights the growing importance of a top–down policy approach in which
global and European commitments influence national policy. Section 2.4 outlines what might be
termed the fifth age of transport policy in Britain in more detail. In particular, it examines the
1998 White Paper, the Daughter and related documents and other relevant legislation and plans
including “Transport 2010”. Section 2.5 outlines other key relevant legislation and lastly,
section 2.6 draws some conclusions.

2.2 The Four Ages of transport policy in Britain
It has been estimated that 79% of Britain’s roads were in place by 1940 and 80% of motorways
were in place before 1980 (Hyder Consulting, 1999). The historical context is therefore
important, particularly given that environmental concerns have only emerged relatively
recently. Button and Gillingwater (1986) divided transport policy in Britain into four ages. The
first age – The Railway Age – lasted from the mid–nineteenth century until the First World War.
The emphasis of policy was on the economic regulation of the railways because of their position
as private monopolies. Between the wars was The Age of Protection , in which the state
concentrated on protecting incumbent operators – particularly the railways – from competition.
The rationale was to prevent wasteful competition and improve safety standards – particularly
on the roads. The period from the Second World War until the late 1970s was termed The Age
of Administrative Planning , in which the transport sector became largely controlled by the state.
The period from the late 1970s was characterised as The Age of Contestability , in which the
idea that transport markets could and should be open to competition (that is, be contestable)
took hold. Key events during this period affecting highways included:
❍ the deregulation of express coach services as a result of the 1980 Transport Act;
❍ the deregulation and privatisation of most local bus services following the 1985 Transport
Act;
❍ the privatisation of the National Freight Corporation (responsible for road haulage) in
1982;
❍ the removal of direct responsibility for building and maintaining roads from the
Department of Transport to the Highways Agency in 1994, and
❍ examination of a number of options for achieving private investment in roads,
culminating in the emergence of a shadow toll system for DBFO (Design, Build, Finance
and Operate) schemes. Private investment in infrastructure provision and operation is
also being introduced via Public Private Partnerships and these arrangements may, in due
course, be used for highway development.

2.2.1 “New Realism”, “The Great Transport Debate” and towards a “Fifth Age” of
transport policy
In the late 1980s, the broad thrust of transport policy began to turn. Arguably, the defining
moment was the publication of the 1989 National Road Traffic Forecast, (NRTF – Department of
Transport, 1989) which predicted, in rough terms, a doubling of road traffic between 1988 and
2025. It was the unsustainability of these forecasts that led to the Trunk Roads Review. Adams
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

15

(1993) calculated that simply providing one additional parking space for each of the 27 million
extra vehicles predicted to join the country’s motor vehicle population would require the
equivalent of a new motorway from London to Edinburgh 257 lanes wide. It is also worth noting
that the forecasts themselves have been revised. The 1997 NRTF projected traffic growth of
almost half that forecast in 1989, for example growth of between 43% and 82% between 1989
and 2026 compared to earlier forecasts of growth of between 83% and 142% between 1988 and
2025 (DETR, 1998a). More recent work by consultants WS Atkins and the DETR has revised the
forecasts back up. For example, the central forecast is now that road traffic will increase by 35%
between 1996 and 2010 compared to a 1997 NRTF forecast of a 28% increase from 1996 to
2011 (CfIT, 1999).
In an influential report (Goodwin et al , 1991), it was argued that there were two main policy
choices in transport planning. Either accept that the increase in car use is inevitable and try and
provide the necessary infrastructure (predict and provide) or control car use in order to keep it
in bounds defined by broader social objectives. Goodwin et al believed that the former policy
had led to unacceptable levels of congestion, accidents, local and global pollution and social
exclusion. They argued that there was a consensus emerging in favour of the second policy
choice that they referred to as the New Realism which supported:
❍ a substantial improvement in the quality and scale of public transport;
❍ increased traffic calming and pedestrianisation;
❍ the use of advanced traffic management systems to increase the operational efficiency of
transport networks;
❍ the adoption of a road pricing system that reflects congestion and other externalities, and
❍ the construction of new roads only where it is desirable to meet demand.
This report was important for at least two reasons. First, New Realism revived interest in the
environmental capacity of roads examined by Buchanan et al (1963) and in road pricing which
had been expounded in the early 1960s by the Smeed Report (Ministry of Transport, 1964).
Secondly, it stimulated the Great Transport Debate that took place in 1995 initiated by the then
Secretary of State for Transport, Brian Mawhinney. This debate focused on three questions that
are worth reiterating because they highlight the potentially contradictory objectives of transport
policy. The questions were:
❍ is the present balance right between economic growth, protection of the environment and
support for personal choice?
❍ if the balance needs to be shifted (for example towards greater environmental protection
or towards enhancing competitiveness by reducing road congestion), what measures
need to be taken and how will they achieve their stated objectives?
❍ are we prepared to accept the wider consequences (for the environment, for personal
choices, for industrial competitiveness, jobs and the economy as a whole) of any such
measures?
The Great Debate culminated in the publication in 1996 of a Green Paper (Department of
Transport, 1996), which accepted that there was a need to pay increased attention to the
environmental impact of transport policy and reduce dependence on the car. Ways of achieving
this would include market–oriented measures, so that transport prices were more aligned with
social costs. Planning oriented measures would also be adopted, including a presumption
against planning permission for out–of–town retailing (Planning Policy Guidance Note 6 –
Department of the Environment, 1996), and a switch in emphasis in investment from roads to
public transport.
The work of two other national bodies in influencing policy change should also be highlighted.
The first was the Standing Advisory Committee on Trunk Road Assessment (SACTRA) which
16

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

originated from the Advisory Committee on Trunk Road Assessment (ACTRA) which produced
the Leitch Report (ACTRA, 1977). The Leitch Report had examined the use of the COBA (Cost
Benefit Analysis) program in road appraisal and identified a major weakness in the assessment
of environmental procedures. Partially as a result, the Department of Transport produced the
Manual of Environmental Assessment (MEA) (1983) to supplement the conventional economic
appraisal. The MEA was substantially revised in 1988 and reformulated to become Volume II of
the Design Manual for Roads and Bridges (DMRB) in 1993 (Department of Transport, 1993).
Two important reports were produced in the 1990s. The first (SACTRA, 1992) recommended that
the assessment of environmental impacts should take place within a cost–benefit analysis
framework thus bringing the economic and environmental appraisals together. The second
(SACTRA, 1994) highlighted the need to take into account the fact that roads generate traffic
and move away from the assumption of a fixed trip matrix which had been standard practice
since the 1960s. The implementation of these two reports might be expected, in totality, to
weaken the case for the construction of new roads.
The second body was the Royal Commission on Environmental Pollution (RCEP), whose
eighteenth and twentieth reports considered transport and the environment (RCEP, 1994, 1997).
The eighteenth report identified eight clear objectives of a sustainable transport policy, along
with 110 detailed recommendations. The objectives were:
❍ to ensure that an effective transport policy at all levels of government is integrated with
land use policy and gives priority to minimising the needs for transport and increasing
the proportion of trips made by environmentally less damaging modes;
❍ to achieve standards of air quality that will prevent damage to human health and the
environment, including full compliance by 2005 with World Health Organisation air
quality guidelines for transport related pollutants;
❍ to improve the quality of life, particularly in towns and cities, by reducing the dominance
of cars and lorries and providing alternative means of access. For example, it was
recommended that the proportion of urban journeys in London undertaken by car should
reduce from 50% to 35% by 2020. In other urban areas, a target of a reduction of the
car’s share of journeys from 65% to 50% by 2020 was proposed;
❍ to increase the proportions of personal travel and freight transport by environmentally
less damaging modes and to make the best use of existing infrastructure. For example
the proportion of passenger–kilometres carried by public transport should be increased
from 12% in 1993 to 30% by 2020 and the proportion of freight tonne–kilometres carried
by rail should increase from 6.5% in 1993 to 20% by 2010;
❍ to halt any loss of land to transport infrastructure in areas of conservation, cultural,
scenic or amenity value unless the land for that purpose has been shown to be the best
practicable environmental option;
❍ to reduce carbon dioxide emissions from transport so that emissions in 2020 are no more
than 80% of the 1990 level;
❍ to reduce substantially the demands which transport infrastructure and the vehicle
industry place on non–renewable materials. For example, the weight of scrapped
vehicles which is recycled should be increased from 77% to 95% by 2015, whilst the
proportion of recycled material used in road construction should be quadrupled by 2015,
and
❍ to reduce noise nuisance from transport to not more than 65 dB L Aeq.16h at the external
walls of housing for daytime exposure and 59 dB L Aeq.8h for night–time exposure.
The twentieth report reviewed progress and concluded that recent action “has been too little
and too slow to provide a substantial shift in transport trends” (page 12). It was concluded that
fuel price increases and improvements in vehicle technology so far planned would not in
themselves bring about the requisite improvements in air quality or reductions in emissions of
greenhouse gases. Needs were identified for rapid innovation in vehicle technology, better
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

17

integration of public transport systems, better integration of transport and land use planning,
better traffic management policies (including greater use of economic instruments) and policies
to encourage modal shift.

2.3 Global and European policy
Another important set of influences on domestic transport policy have been the external
influence of global and European policy initiatives.

2.3.1 Global policy
The Rio Earth Summit provided a blueprint for a global strategy toward a sustainable future
(UNCED, 1992). Local Agenda 21 groups have been set up to determine detailed procedures
for implementation using the slogan “Think Global, Act Local”. At the follow–up Kyoto climate
change conference in December 1997, the UK Government committed itself to a legally binding
target to reduce greenhouse gas emissions to 12.5% below 1990 levels by the period 2008 to
2012. This reduction is equivalent to 27 million tonnes of carbon. In addition, the UK
Government has a domestic aim to reduce CO 2 emissions to 20% below 1990 levels by 2010.
It was partly because of the increased emphasis on improving air quality that resulted from the
Rio and Kyoto summits that the UK Government introduced the Fuel Price Escalator in which
fuel duty would rise by at least five percent per annum in real terms from 1994. This was
increased to six percent in 1997. The RCEP (1994) had recommended an increase of nine
percent per annum. In 1999, it was announced that the commitment to the Fuel Price Escalator
would be abandoned, with any increase in fuel duty above inflation hypothecated for transport
expenditure.

2.3.2 European transport policy
Articles 74 to 79 of the 1957 Treaty of Rome provided the basis for a Common Transport Policy
(CTP) for the then European Community. However, as Glaister et al (1998) point out, progress
was slow until 1985 when the European Court of Justice declared that the inland transport of
passengers and freight should be open to all Community firms without discrimination as to
nationality or place of establishment. In the same year, the Commission’s White Paper on the
completion of the internal market (and the subsequent 1986 Single European Market Act) placed
transport at the forefront of move towards the completion of the single market that was finally
achieved in 1992.
In 1992 the European Commission also published a White Paper on the CTP (European
Commission, 1992), which was adopted the following year. The White Paper marked an
important change in emphasis for the CTP which had previously been geared towards the
elimination of artificial barriers (although many such barriers continue to exist or were only
removed since 1992 – see Preston, 1999). It now provides a more comprehensive policy, with
the main objective of promoting sustainable mobility through improving the quality of transport
systems, in terms of competitiveness, safety and environmental impact (see also European
Commission, 1995). The CTP has been adapted to confront the new challenges facing post 1992
transport policy. In particular, the Maastricht Treaty, which was finally ratified in 1993, required
the integration of environmental objectives.
However, actions that can be taken at a European level are limited by the subsidiary principle
in which transport policy is delegated to national, regional or local governments. The
Directorate General of the European Commission responsible for transport (formerly DGVII and
now DG Transport) has only a limited number of policy instruments at its disposal. The most
important are directives and regulations that aim at the harmonisation of technical, fiscal and
18

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

social provisions. Of particular importance to this chapter are the attempts to harmonise vehicle
emission standards, which are discussed below. Another example is the Integrated Pollution
Prevention and Control Directive (61/96) which came into effect in October 1999.

2.3.3 The European Auto–Oil Programme
An important development at the European level has been the Auto/Oil Programme that was designed
to determine emission standards to apply from 2000. The programme involved the European
Commission in conjunction with Europia and ACEA, the European Trade associations for the oil and
motor industries respectively. The work programme consisted of (European Commission, 1996):
❍ air quality studies to predict future air quality in seven European cities (Athens, Cologne,
The Hague, London, Lyon, Madrid and Milan) and, for ozone, across the European
Union. Emission reduction targets were to be determined for carbon monoxide,
particulate matter, benzene, nitrogen dioxide and tropospheric ozone;
❍ the European Programme on Emissions, Fuels and Engine Technology – a joint motor and
oil industries research programme to investigate the effects of vehicle technology and
fuel characteristics on emissions, and
❍ a cost–effectiveness study in which the costs and emissions impact of a range of
abatement techniques were collated and the most cost–effective package of measures to
meet the emission reduction targets identified.
As a result of the Auto/Oil work the limit for particulate emissions from diesel passenger
vehicles was reduced from 0.08g/km (Stage II) to 0.05g/km in 2000–01 (Stage III) and 0.025g/km
in 2005 (Stage IV). Limits for diesel and petrol passenger vehicles are also set for carbon
monoxide, hydrocarbons and nitrogen oxides (see, for example, RCEP, 1997, p23). Similarly, the
permitted sulphur content of diesel was reduced from 3000ppm to 2000ppm in October 1994
and to 500ppm in October 1996. The sulphur content of petrol was reduced from 1000ppm to
500ppm in January 1995.

2.4 Current UK transport policy
2.4.1 The 1998 White Paper
In July 1998 the Labour Government published the White Paper A New Deal for Transport: Better
for Everyone (DETR, 1998b). Although this was intended as an United Kingdom policy document,
separate documents were also produced for Northern Ireland, Scotland and Wales (see, for
example, Secretary of State for Scotland, 1999). For reasons of brevity, this chapter focuses on
the important transport policies as they affect the majority of the United Kingdom, but it should
be recognised that there are differences in emphasis in different regions. The White Paper, which
was a culmination of the internal policy pressures discussed in section 2.2.1 and the external
policy pressures discussed in section 2.3, may be seen as an important stage in a fifth age of
British transport policy which might be termed The Age of Integration . In the words of the
Secretary of State, John Prescott, “The White Paper is about…radical change and how to achieve
it”. The White Paper’s aims are manifold but may be summarised under 12 key headings:
1. An integrated transport policy based on integration within and between different types of
transport, integration with the environment, integration with land–use planning and integration
with policies for education, health and wealth creation.
2. Better policy at the national level , including a new independent Commission for Integrated
Transport (CfIT), tackling the “pinch–points” in transport networks that lead to congestion and a
new airports policy with a stronger role for regional airports.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

19

3. Better policy at the regional level , with many decisions on transport issues devolved to the
Scottish Parliament and the Northern Ireland and Wales Assemblies. Strengthened planning
arrangements in the English regions will secure integration between transport and land use,
whilst the Mayor for London will be required to produce an integrated transport strategy.
4. Better policy at the local level , including new five year Local Transport Plans, new local
powers including road user charging and levies on parking, new sources of additional funding
for local transport and decision making on transport to be more accountable to local people.
5. Better buses , including up–graded quality partnerships and exclusive quality contracts, a
nation–wide half price concessionary fare scheme for the elderly and special funding for buses
in the countryside.
6. Better trains , through the creation of a Strategic Rail Authority (SRA), passenger dividends
from passenger railway companies and tougher regulation.
7. A better environment , through greener, more fuel–efficient vehicles promoted by better
standards, tax incentives and a cleaner vehicle task force; new powers to enforce noise controls
at airports; the promotion of traffic management, traffic calming and traffic reduction (an
aspiration to reduce traffic by ten percent is hinted at) and through making cycling and walking
easier and safer.
8. Better safety and security , through a root and branch review of transport safety; a new road
safety strategy and targets to reduce accidents; safe routes to school; a major review of speed
policy; safer public transport; changes in drivers’ hour legislation; a review of the role of the
British Transport Police and implementation of a secure stations scheme.
9. Better freight transport , through quality partnerships between local authorities and operators
on lorry routing and delivery hours; greater use of 41 tonne, six axle lorries; improvements in
best practice; impounding illegally operated lorries; facilitating shipping; extending freight
grants to include coastal and short sea shipping and promoting rail freight through the Strategic
Rail Authority.
10. A new deal for motorists , including improved management of the trunk road system through
Regional Traffic Control Centres; investment focused on improving reliability of journeys; better
maintained roads; an updated Highways Agency Road User’s Charter; more help for motorists if
they break down on the motorway; a reduction in the disruption caused by utilities’ street work;
improved road safety and safer cars; quality information for the driver; dealing with car crime;
more secure car parks; better information and protection when buying a car; action on
“cowboy” wheel clampers; more fuel–efficient cars and less congestion on the roads and less
pollution in cars.
11. A new deal for the public transport passenger through more and better buses and trains; staff
trained in customer care; a stronger voice for the passenger; better information including a
national public transport information system by 2000; better interchanges and connections;
enhanced networks with simplified fares and better marketing; more through–ticketing and
travelcards; more reliable buses through priority measures and reduced congestion and easy
access to public transport.
12. Everyone doing their bit , including: Government departments taking the lead in introducing
“green transport plans”; local authorities, businesses, community organisations, schools and
hospitals encouraged to produce their own green transport plans; a major national awareness
campaign; a new initiative on school journeys and individuals/families/communities
considering their own travel habits.
20

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Overall, the White Paper hopes that the new deal for transport will lead to more choice, a more
inclusive society, better places to live, a more sustainable economy and greater sharing of
decisions. The response to the White Paper was generally positive. For example, a straw poll of
17 experts in Local Transport Today (1998) found only one dissenting voice. However, there are
also some important concerns. Mackie (1998) raises four areas of concern. The first is that there
is some vagueness about the nature of the problem and hence about policy objectives. The
emphasis is on congestion and environmental externalities of transport but there is a danger of
swinging from one polar position – that traffic growth is unequivocally good, a symbol of the
great car economy – to the other in which traffic growth is unequivocally bad and must be
reined back always and everywhere. A moderated view might be that although total traffic
growth may be seen as undesirable, local growth might be more or less desirable within an
overall national limit. Secondly, there are some concerns about the strategic direction of policy,
with an over–emphasis on pricing mechanisms and an under–emphasis on capacity
enhancement, particularly for the inter urban roads network, for example the speed
management exercises on the M25. Thirdly, there are concerns about the potential of public
transport as an instrument for coping with traffic growth. Little attention has been paid to the
fact that the cross–elasticity of car demand with respect to public transport attributes is, on
average, very low. The fourth issue is the need for action. Concerns include the lack of a firm
legislative programme, the lack of measurable targets, the lack of the necessary finance to make
change happen, the passing of responsibilities for difficult problems down to local authorities
and the danger that the new QUANGOs (such as SRA and CfIT) will slow down not speed up
policy implementation. These concerns have been partially addressed by the publication in
November 1999 of a 231 clause, 258 page Transport Bill, with the most important provision
being the granting of powers to local authorities to introduce road user charging and workplace
parking levies. Full details of Bills before parliament may be found at www.parliament.uk

2.4.2 The Daughter Documents
The White Paper was accompanied by nine “daughter documents”. The six most important
documents with respect to roads are discussed in turn.
The New Deal for Trunk Roads in England (DETR, 1998c) undertook a major trunk roads review
in which 37 schemes were accepted and, by being cancelled or left for local authority
decisions, 36 rejected. Somewhat perplexingly, both sets of schemes seem to have average
benefit cost ratios of 3:1 (Mackie, op cit ). Decisions on a further 44 schemes were deferred
pending further study (Price, 1999). These decisions were based on a New Approach to
Appraisal (NATA) which is discussed in more detail in DETR (1998d and 1998e). The key
development is that in addition to impacts on the economy and safety (largely measured by
COBA), impacts also need to be taken into account that affect the environment, accessibility
and integration (see Table 2.1). The results are brought together in an Appraisal Summary Table
(AST) which brings together quantitative and qualitative indicators (see Table 2.2). With respect
to the environment, the essential measures are as follows:
❍ for noise , the number of residential properties for which the difference in the assessment
year levels between the do minimum and “with proposal” options is 3dB(A). In the
example in Table 2.2 (an upgrade of the A1) it can be seen that a net total of 670
properties benefit from the scheme;
❍ for local air quality , changes in the emission of PM 10 s (measured in micrograms per cubic
metre – (µg/m 3 ) and NO 2 (measured in parts per billion). Differences in emissions should
be multiplied by the number of weighted properties on the route (where a property within
50m of the roadside has a weight of 1.00 and those within 150m to 200m have a weight
of 0.50 {PM 10 } and 0.55 {NO 2 }). The scheme in Table 2.2 leads to a reduction in
exposure to PM 10 s and NO 2 ;
❍ for global emissions , changes in the level of carbon dioxide, measured in tonnes. The
scheme in Table 2.2 leads to an increase in emissions of CO 2 .
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

21

Criteria

Sub–Criteria

Environmental Impact*

Noise
Local Air Quality
Landscape
Biodiversity
Heritage
Water

Safety

not sub–divided

Economy
.

Journey Times and Vehicle
Operating Costs
Journey Time Reliability
Scheme Costs
Regeneration

Accessibility

Access to Public Transport
Community Severance
Pedestrians and Others

Integration

not sub–divided

*Environmental Impact also includes data on change in CO 2 emissions.
Source: Price, 1999, page 224

Table 2.1: Criteria and Sub–Criteria used in the New Approach to Appraisal.
❍ for landscape , the approach involves a description of the character of the landscape and an
evaluation of what matters in the landscape and why. The latter is achieved by developing
a matrix of features against indicators (referred to as Worksheet 6.2). Features considered
are: pattern, tranquillity, culture, landcover and summary of character. Indicators include:
description, scale, rarity, importance and substitutability, impact and additional mitigation.
Impact is measured on an eight–point scale, based on a seven–point scale devised by the
Countryside Commission but including a category for a very large adverse effect. The
impact of the scheme in Table 2.2 is judged to be slightly adverse.
❍ for biodiversity , the approach involves a description of the nature conservation
evaluation of the habitats, species and natural features affected and an assessment of the
ecological features. A list of attributes should be considered (referred to as Worksheet
6.3) including site, scale, importance, rarity, substitution possibilities, nature
conservation evaluation and impact. Using a methodology derived from English Nature,
nature conservation evaluation is based on a five–fold classification illustrated by Table
2.3. Impacts are again measured on an eight point semantic scale. Nature conservation
evaluation and impact are combined to produce an assessment score as shown by Table
2.4. The scheme in Table 2.2 is judged to be slightly adverse.
❍ Heritage is also assessed using a matrix, referred to as Worksheet 6.4. The rows are the
definition of features in terms of form, survival, condition, complexity, context and
period. The columns involve description, scale, significance, rarity and impact. Using
advice from English Heritage, an overall assessment score may be developed based on
the guidance matrix illustrated by Table 2.5. The scheme in Table 2.2 is judged to be
neutral.
22

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Table 2.2: Appraisal Example.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

23

NAQS NO2 objective exceeded along scheme and PM 10 level
increases by 2µg, but no properties close
No significant impact. Some areas to north of scheme
designated by LAs as of Special Landscape Value
No significant direct impact. But some habitats over 0.5km to
the south of Micklefield and close to Fairburn Ings SSSI affected
Benefits to the Old Bridge across the River Aire at Ferrybridge
(a scheduled monument), balanced by impact on Ferrybridge Henge
(also a scheduled monument). Mitigation for latter agreed
Assuming effective mitigation, risk of damage to the water
environment is likely to be negligible

Local air
quality

Landscape

Biodiversity

Heritage

Water

CO 2 tonnes added
2000–5000

COBA

I NTEGRATION

A CCESSIBILITY

Maintenance delay savings of £250

E CONOMY

Little impact on pedestrians and others

Pedestrians and others

Consistent with West Yorkshire Transport Package, Leeds and
Wakefield UDPs and Regional Planning Guidance

Significant reduction in community severance in villages of
Fairburn, Brotherton and Ferrybridge (over 680 dwellings in total)

Severance

–

Small number of public transport journeys on route limit potential benefit

Public transport

Serves West and South Yorkshire Assisted Area and Yorkshire and
Humberside ERDF Objective 2 areas

–

Reliability

Regeneration

–

Cost

Journey times
& VOCs

Accident savings cover nearly half of the costs

S AFETY

Over 2500 properties would experience a slight increase
in noise without the scheme

Noise

Qualitative Impacts

Sub–Criteria

E NVIRONMENTAL
I MPACT

–

inter–peak
1.4 mins

PVB £337m PVC £91m

–

–

–

–

BCR 3.7

Neutral

Neutral

Large
+ve

Neutral

Yes

Large
Low rel to PVC

PVC £91m

PVB £300m
330% of PVC

PVB £39m
43% of PVC

Neutral

Neutral

Slight –ve

Slight –ve

–236 PM 10 *
–994 NO 2 *

net 670
properties
win with
scheme*

Assessment

NPV £245m

Serves regeneration area?
Development depends on scheme?

Route stress
before 142% after 53%

peak
3.1 mins

Accidents Deaths Serious Slight
700
60
510
590

–

–

–

–

No. properties experiencing:
– improved air quality 94
– worse air quality 0

No. properties
experiencing (w/s):
– Increase in noise 10
– Decrease in noise 680

Quantitative Measure

72,000 vpd (27% HGV). Poor safety due to poor alignment and accesses/minor junctions on existing D2AP. Lengthy delays especially during maintenance. Community
severance in Ferrybridge and Fairburn where properties affected by high noise levels and air pollution.
A1 in this area caters mainly for long distance traffic, including many HGVs. Public transport solutions would not cater for sufficient traffic to relieve problem. On–line
widening would require substantial demolition of properties.

1996 scheme – off line 16.3 km upgrade to D3M Cost £160m

Criteria

OTHER OPTIONS

PROBLEMS

A1(M) Ferrybridge to Hook Moor

Category A
Ramsar Sites (Convention on Wetlands of International Importance especially as Waterfowl
Habitat, 1971)
World Heritage Sites (Convention for the Protection of World Cultural & Natural Heritage, 1972)
Biosphere Reserves (UNESCO Man & The Biosphere Programme)
European Sites (EC Habitats Directive 1992 & UK Habitats Regulations 1994):
Special Areas of Conservation (SACs)
Special Protection Areas (SPAs)
Sites of Community Importance (SCIs)
Candidate SACs and potential SPAs
Sites hosting habitats/species of European Community interest (Annex 1 and 2 of Habitats
Directives)
Sites hosting species listed under the Bonn Convention (Convention on the Conservation of
Migratory Species of Wild Animals)
Sites hosting species under the Berne Convention (Annex 1 and 2 of the Convention on the
Conservation of European Wildlife and Natural Habitats, 1979)
Biogenetic Reserves under the Council of Europe
European Diploma Sites under the Council of Europe

Category B
Sites of Special Scientific Interest and National Nature Reserves (Wildlife & Countryside Act
1981 as amended and National Parks and Access to the Countryside Act 1959)
Sites with Limestone Pavement Orders (Wildlife & Countryside Act 1981)
Nature Conservation Review Sites (NCR)
Geological Conservation Review Sites
Marine Nature Reserves (Wildlife & Countryside Act 1981)
Areas of Special Protection for Birds (Wildlife & Countryside Act 1981)
Sites hosting Red Data Book species
Sites hosting species in Schedules 1, 5 and 8 of the Wildlife & Countryside Act 1981.

Category C
Local Nature Reserves (National Parks and Access to the Countryside Act 1949)
Other sites (not described above) with Biodiversity Action Plan (BAP) priority habitats/species
Sites of Importance to Nature Conservation (SINCs) and other local designations
Regionally Important Geological Sites (RIGS)
Other natural/semi–natural sites of significant biodiversity importance, not referred to above.

Category D
Sites not in the above categories, but with some biodiversity or earth heritage interest.

Category E
Sites with little or no biodiversity or earth heritage interest.
Note: Sites falling into more than one category should be classified into the most important
category.
Source: DETR, 1998e

Table 2.3: Guide to Nature Conservation Evaluation.
24

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

❍ Water Quality and Land Drainage/Flood Defence are assessed using a risk–based
approach to determine potential negative impacts, based on guidance provided by the
Environment Agency. Seven indicators are examined: General Quality Assessment (GQA)
grade (Chemical), EC Freshwater Fisheries Directive, water abstraction points,
groundwater vulnerability, location of boreholes, floodplain, watercourses, river
corridors and flood risk. These indicators are assessed in terms of sensitivity and the
potential of the proposal to cause harm, using a three–point scale (high, medium and
low). These assessments are converted into an overall score using the information given
by Table 2.6. The approach is modified to take into account the scope for mitigation and
enhancement. The scheme in Table 2.2 is judged to be neutral.

Nature conservation
Evaluation

Impact

Assessment score

(1)
(2)
(3)

Category A
Category A
Category A

+ Major negative
+ Intermediate negative
+ Minor negative

= Very large adverse
= Large adverse
= Slight adverse

(4)
(5)
(6)

Category B
Category B
Category B

+ Major negative
+ Intermediate negative
+ Minor negative

= Very large adverse
= Large adverse
= Slight adverse

(7)

Category C

+ Major negative

(8)
(9)

Category C
Category C

+ Intermediate negative
+ Minor negative

= Large or Moderate
adverse (see note F)
= Moderate adverse
= Slight adverse

(10) Category D

+ All negative categories

= Slight adverse

(11) Category E

+ All negative categories

= Neutral

(12)
(13)
(14)
(15)

+
+
+
+

=
=
=
=

All
All
All
All

categories
categories
categories
categories

Neutral
Minor positive
Intermediate positive
Major positive

Neutral
Slight positive
Moderate positive
Large positive

Notes:
(A) Options that have a “very large adverse effect” are likely to be unacceptable on nature conservation
grounds alone (even with compensation proposals).
(B) There should be a strong presumption against options in the "large adverse" category, with more than
1:1 compensation (net gain within the Natural Area) for the very occasional cases where development
is allowed as a last resort.
(C) Options in the “moderate adverse” category should include at least 1:1 compensation (no net loss
within the Natural Area) if the development is allowed.
(D) See Annex 6A for the definition of nature conservation evaluation categories.
(E) See the main text for definition of impact.
(F) Circumstance (7) above should score “large adverse” if the habitats/species are not substitutable, or
otherwise should score “moderate adverse”.
Source: DETR, 1998e

Table 2.4: Decision Rules to Assist the Assessment of Options on Nature Conservation.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

25

❍ Severance is often considered as an environmental impact but is treated in the NATA
under the heading of accessibility. Severance is measured on a three–point scale (slight,
moderate and severe/substantial). The numbers of pedestrians affected by new severance
and relieved from existing severance are recorded (in worksheet 8.3). The overall
assessment may be neutral, slight, moderate or large. In the case of the scheme in Table
2.2 there is a large beneficial impact because there is relief from severe severance
affecting a large number of households.
Overall for the scheme in Table 2.2, the present value of benefits (PVB) is £337m and the
present value of costs (PVC) is £91m, resulting in a net present value (NPV) of £245m and a
benefit cost ratio (BCR) of 3.7. On conventional economic grounds, the scheme would go
ahead. The AST show that there are no serious adverse environmental impacts (indeed, there are
some substantial benefits). Similarly, the scheme is either neutral or beneficial with respect to
accessibility and integration. Under the NATA, the scheme remains in the roads programme
(Targeted Programme of Improvements).

Assessment Score Guidance Matrix
S CALE

E FFECT
P HYSICAL

I NTERNATIONAL
Very Large
Large
Very Large
Large
Very Large
Very Large

M AJOR
PARTIAL
M AJOR
S LIGHT
M AJOR
S LIGHT

V ISUAL
S ETTING
C UMULATIVE

N ATIONAL
Large
Large
Large
Large
Very Large
Large

R EGIONAL
Moderate/Large
Slight
Large
Slight
Large
Large

Source: DETR, 1998e

Table 2.5: Determinants of an Assessment Score for Heritage.

Sensitivity of
the Environment
High
Medium
Low

Key:

–3*
–3
–2
–1
0

–2
–1
0
Low

–2
–2
–1
Medium
Potential to Cause Harm

–3*
–3
–2
–2
High

Very large negative effects
Large negative effects
Moderate negative effects
Slight negative effects
Neutral

Source: DETR, 1998e

Table 2.6: Determinants of an Assessment Score for Water Quality and Land Drainage/Flood
Defence.
26

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

More detailed advice on the application of the NATA to 17 of the 44 deferred schemes in which
multi–modal solutions might be feasible has also been produced and is referred to as the
Guidance On Methodology for Multi–modal Studies (GOMMS – MVA et al , 1999). Particular
advice is given on public consultation, the generation of options, the formulation of strategies
and plans, objective setting and problem identification, effectiveness of policy instruments,
modelling and appraisal.
The advantages of the NATA include its attempt to bring together quantitative and qualitative
indicators together in one summary table. It is perhaps too succinct in this. It is also relatively
transparent as an appraisal process, although the policy prescriptions that have emerged in the
Roads Review are less transparent. According to Glaister (1999) it goes as far towards
multi–criteria analysis as is sensible. However, despite warnings from the DETR, there may be
near irresistible temptations to bring together individual scores to form an aggregate overall
score, which would erroneously assume ordinal measures are cardinal. Dangers of double
counting would also seem to have increased.
The other five roads–related daughter documents may be discussed in slightly less detail. The
bus policy document, From Workhorse to Thoroughbred (DETR, 1999a) proposes to increase the
role played by the bus in transport policy and promote a shift in the planning and allocation of
road space from the car to the bus.
The daughter document on road user and workplace parking charging policy, Breaking the
Logjam (DETR, 1998f) is essentially a consultation document. It poses a number of
implementation questions concerning the proposals to grant local authorities powers to charge
for the use of congested roads and raise a workplace parking levy. There are also proposals for
charging on motorways and trunk roads. In conjunction with this consultation, trials of
electronic road pricing have been proposed in Edinburgh and Leeds. The Mayor of London and
the London boroughs have been given charging powers in the Greater London Authority Act
(1999). Details of this Act and all other Acts passed since 1995 may be found on
www.hmso.gov.uk
The daughter document on freight policy, Sustainable Distribution: A Strategy, sets out a series of
policies to promote the sustainable transport of goods (DETR, 1999b). This also involves integration
within the freight sector and with planning and road policies, the integration of distribution
infrastructure, and the promotion of rail freight, coastal shipping and inland waterways. One of the
important outstanding issues surrounds the case for the 44 tonne, six axle lorry, following the
authorisation for 40 tonne, five axle and 41 tonne, six axle lorries in January 1999.
Road safety policy has also been reviewed. New targets for casualty reduction have been set
(DETR, 2000a) to cover the next decade. Furthermore, greater emphasis is being given to speed
reduction (DETR, 2000b). Both documents will have implications for the highway environment
as local authorities aim to achieve slower vehicle speeds.
Local authorities are required to produce Local Transport Plans (LTPs) (DETR, 2000c and 2000d)
covering the five–year period 2001–02 to 2005–6 both to provide a strategy and to bid for funds
from central government. Funding will be awarded for the first year only with an Annual
Performance Review to determine funding subsequent funding levels. Key elements with respect
to the environment include the need to co–ordinate with any air quality action plan; action on
noise and action on climate change; the need to recognise the particular needs and special
character of the countryside and the promotion of measures to encourage voluntary adoption of
green transport plans. Appraisal is to be based on the guidance of the new approach to appraisal
(GNATA), discussed above, and on the appraisal summary tables exemplified by Table 2.2.
Table 2.7 shows the recommended approach to LTP appraisals. It is apparent that LTPs will be
the important delivery mechanism for the White Paper’s transport policies.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

27

2.4.3 Related documents
The National Air Quality Strategy (NAQS) (Department of Environment, 1997) has two
objectives:
❍ “to achieve full compliance by 2005 with World Health Organisation (WHO)
health–based air quality guidelines for transport–related pollutants”, and
❍ “to establish, in appropriate areas by 2005, local air quality standards based on the
critical levels required to protect sensitive ecosystems”.
The initial standards and objectives are shown by Table 2.8, although they have since been reviewed
and revisions are likely (DETR, 1999e). An important tool for delivering the NAQS is the system of
Local Air Quality Management. Local authorities have a duty to assess air quality to determine
whether the objectives prescribed in the Air Quality Regulations, 1997 are likely to be met.
An important concept is that of sustainability, which using the Brundtland definition means the
ability to meet the needs of current generations without compromising the needs of future
generations. Sustainability is often sub–divided into environmental, economic and social
sub–components. It can be a vague concept but a sustainable framework for transport policy
was outlined in the Sustainable Development Strategy for the UK (Cm2426, 1994). The UK
Round Table for Sustainable Development (1996) added more detail in terms of policy definition
and on the environmental and economic policies required to achieve the objectives.
One important aspect of policy is the series of circulars, good practice guides, Mineral Planning
Guidance Notes (of which MPG 6 on guidelines for aggregates provision in England and Wales
is important for highways) and Planning Policy Guidance Notes (PPGs) produced by the DETR.
Full details may be found on www.detr.gov.uk. Three PPGs have been recently revised, subject
to consultation. PPG 12 proposes the production of better development plans and describes
how they should integrate with LTPs. PPG 11 provides advice on the preparation of Regional
Transport Strategies as an integral part of Regional Planning Guidance. PPG 13, first issued in
1994 and revised in October 1999, aims to integrate planning and transport at the national,

Appraisals
LTP with no
major scheme

Simplified AST for
preferred strategy

Simplified AST for
alternative strategies
tested

LTP with major
road scheme

Simplified AST for
preferred strategy
with road scheme

Appraisal of the road
scheme, as specified in
the GNATA
(against the do minimum),
to inform the simplified AST

LTP with major
PT scheme

Simplified AST for
S56 and full cost benefit
preferred strategy with appraisal of the PT scheme,
PT scheme
to inform the AST

Simplified AST for
Simplified
preferred alternative AST for
strategy without road additional
scheme
alternative
strategies
tested
Simplified AST for
preferred alternative
strategy without PT
scheme

Simplified
AST for
additional
alternative
strategies
tested

Source: DETR, 1999d.

Table 2.7: Appraisal Procedure for LTPs.
28

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Standard
Benzene

Objective
Sites at which standard was exceeded in 1995
5 ppb as running annual achieve standard by 2005 none, but likely to be exceeded at the side of
mean (EPAQS)
heavily trafficked urban roads

1,3–butadiene 1 ppb as running annual achieve standard by 2005
mean (EPAQS)

none; unlikely to be exceeded except at a few
urban background sites (or at the side of heavily
trafficked roads)

carbon
monoxide

10 ppm as running
8–hour mean (EPAQS)

achieve standard by 2005

West London (4 exceedances on two days) and
Belfast City Centre (13 exceedances on
three days)

lead

0.5 (µg/m 3 as annual
mean (WHO)

achieve standard by 2005

a few industrial monitoring sites: unlikely to be
exceeded in urban areas

nitrogen
dioxide

150 ppb as 1–hour mean achieve both standards by
(EPAQS) 21 ppb as
2005
annual mean (WHO)

ozone

50 ppb as running
8–hour mean (EPAQS)

achieve standard at 97th
percentile by 2005 (that is,
standard can be exceeded
on 10 days of the year at
any site)

frequent exceedances at both urban and rural
sites, with greater frequency in uplands and parts
of south–east England closest to the
continent and lowest frequency in Scotland and
Northern Ireland

fine particles
(PM 10 )

50 (µg/m3 as running
24–hour mean (EPAQS)

achieve standard at 99th
percentile by 2005 (that is,
standard can be exceeded
on 4 days of the year at
any site)

some urban sites on up to 40–50 days, especially
in London, Liverpool, Swansea and Belfast
(where coal is still a major domestic fuel);
all urban sites between 1992 and 1995, winter
and summer, with higher readings in winter

sulphur
dioxide

100 ppb as 15–minute
mean (EPAQS)

achieve standard at 99.9th
percentile by 2005 (that is,
standard can be exceeded
for 35 15–minute periods
during the year at any site)

all except the two most remote continuous
monitoring sites, with highest frequency in
industrial and coal–burning areas; grounding
of plumes from power stations also a factor

for 1–hour mean, seven urban sites on up to five
days each (all but two urban sites would have
exceeded the annual standard), no rural sites

objectives in italics are provisional
EPAQS – standard recommended by the UK Expert Panel on Air Quality Standards
WHO – guideline recommended in the latest revision of the World Health Organisation Air Quality Guidelines (not yet
published)
Source: RCEP, 1997

Table 2.8: National Air Quality Strategy: standards, objectives, reported exceedances in 1995.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

29

regional, strategic and local levels to promote more sustainable transport choices and reduce
the need to travel, especially by car. Specific advice includes:
❍ focus on the major generators of travel demand in city, town and district centres and near
to major public transport interchanges;
❍ locate local facilities in local centres which are accessible by walking and cycling;
❍ accommodate housing principally within existing urban areas, with increased densities
for both housing and other uses at locations which are highly accessible by public
transport, walking and cycling;
❍ in rural areas, locate development for housing, jobs, shopping, leisure and services in
local service centres;
❍ use parking policies to reduce reliance on the car for work and other journeys;
❍ give priority to people over traffic in town centres, other areas with a mixture of land uses
and local neighbourhoods and give more road space to pedestrians, cyclists and public
transport in these locations;
❍ ensure that the needs of disabled people are taken into account, and
❍ protect sites and routes which could be critical in developing infrastructure to widen
transport choices.

2.4.4 Transport 2010: The 10 Year Plan
In July 2000, the Government produced “Transport 2010” (DETR, 2000e), described by the
Secretary of State, John Prescott, as a “ten–year route map” designed to achieve the goals set
out in the 1998 White Paper.
The approach outlined in Transport 2010 is based upon:
❍ integrated transport: looking at transport as a whole, matching solutions to specific
problems by assessing all the options;
❍ public and private partnership: government and the private sector working more closely
together to boost investment, and
❍ new projects: modernising the transport network in ways that make it bigger, better, safer,
cleaner and quicker.
Transport 2010 envisages that some £180bn will be necessary over the next ten years. Public
investment will account for £64.7bn, private investment for £56.3bn with the remainder
(approximately £59bn) coming from public revenue. The investment programme will provide for
roads, railways and local transport (including London) in roughly equal shares.
Key features that the programme is expecting to deliver are:
❍
❍
❍
❍
❍
❍
❍
❍
❍
❍
❍
30

reduced congestion on the road network;
modern trains with better services and reduced fares;
a 50% increase in passenger use of the railway;
resources to enable the Mayor of London to reduce over crowding on the Underground
and congestion in London – with £3.2bn investment in the first three years;
100 new bypasses;
360 miles of trunk road and motorway widening;
improvements in rural transport;
better bus services and a 10% growth in passenger use;
up to 25 new light rail projects in major cities;
safer roads and railways, and
lower emissions and better air quality.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

As far as the highways sector is concerned a number of substantial targeted improvements are
outlined. These include:
❍ bottlenecks eased by targeted widening of 360 miles of the strategic road network;
❍ 80 major trunk road schemes to improve safety and traffic flow at junctions;
❍ 100 new bypasses on trunk and local roads to reduce congestion and pollution in
communities;
❍ 130 other major local road improvement schemes;
❍ completion of the 40 road schemes in the Highways Agency Targeted Programme of
Improvements;
❍ 60% of the trunk road network given lower–noise surfaces;
❍ elimination of the maintenance backlog for local roads, bridges and lighting as part of a
£30bn programme;
❍ HGV lanes on congested strategic routes to provide priority for lorries and safer lanes for
cars;
❍ smarter management of the trunk road network, giving drivers better information on
traffic conditions;
❍ 40% reduction in the number of people killed or seriously injured in road accidents, and
❍ accelerated take–up of cleaner vehicles to reduce air pollution and CO 2 emissions.

2.5 Other key legislation
There is a myriad of legislative statutes relevant to the environmental management of highways.
Perhaps the most important act is The Highways Act 1980, which was amended in 1999 to
implement EC directive 85/337/EEC and subsequent amendment 97/11 on “The assessment of
the effects of certain public and private projects on the environment”. This, and related
legislation, are discussed in detail in Transport in the Urban Environment (IHT, 1997, especially
chapters 4 and 33). The key environmental legislation is the Environment Act 1995 which
further prioritised environmental protection. Much of the relevant legislation in this area is
described in Volume 11 of the Design Manual for Roads and Bridges , particularly with respect
to conservation legislation (section 3, part 4, annex III). The 1981 Wildlife and Countryside Act,
which established Areas of Special Protection for birds (AOSPs) and Sites of Special Scientific
Interest (SSSI), is particularly influential, as can be seen from Table 2.3.
More recently, the 1997 Road Traffic Reduction Act requires local authorities to assess traffic
levels, forecast expected growth rates and consider targets. This was strengthened by the 1998
Road Traffic Reduction (National Targets) Act that requires the Minister to set targets and pursue
other solutions. The Commission for Integrated Transport advises that a “single national
end–year target on road traffic or resultant congestion levels will not be the best tool to
confront congestion or other problems arising from road traffic”. Instead a matrix of
benchmarking profiles is recommended based on three dimensions: different area types; traffic
levels and congestion outcomes and packages of measures based on key policy scenarios.

2.6 Conclusions
2.6.1 The increasing influence of environmental issues
This review of transport policy in the UK has indicated that although there was some concern
for environmental impacts in the previous four ages of domestic transport policy, environmental
effects have probably only been given adequate weight in the last decade as the fifth age of
transport policy has emerged. Similar changes have occurred in other sectors of economic
activity, with the publication of This Common Inheritance being a key turning point
(Department of the Environment, 1990).
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

31

Accidents
Noise
Air Pollution
Climate change
Total

Peirson, Skinner and
Vickerman

Mauch and
Rothengatter

0.58
0.08
0.17
0.03
0.86

1.84
0.28
0.70
0.46
3.28

– 1.33
– 0.39
– 0.43
– 2.18

Note: Mauch and Rothengatter’s results have been converted from ECUs to pounds using an
exchange rate of 1.4284 ( Source: Economic Trends Annual Supplement, 1994 Edition. HMSO London. Table 5–1).
Source: Peirson, Skinner and Vickerman (1994); Mauch and Rothengatter (1995) Quoted by Nash (1997)

Table 2.9: UK Unit External Costs 1991. (car) (p/pass km)
This change has been characterised as a shift from the age of contestability to the age of
integration, with the tipping point year being 1998, although the process of change has
spanned a decade. One of the key features is the integration of transport policy with
environmental policy. This is particularly reflected by the New Approach to Appraisal.
Arguably, similar policy changes have taken place at the global and European levels but to
different degrees and with different timescales. In Europe, initial emphasis of the CTP was on
introducing the age of contestability, although liberalising reforms have been introduced much
more gradually than the big bang approach favoured by the UK, with the process still
incomplete, particularly for railways. However, since the White Paper of 1992 there has been
a greater emphasis on the environment at a European level and the emergence of an age of
integration but with greater emphasis on network integration (and hence interest in concepts
such as interoperability, intermodality and interconnection) and social co–ordination.
One interesting area of speculation relates to how long the new age of integration might last.
This is likely to be dependent on the outcome of some important test cases, including the M4
Bus Lane and the Oxford Transport Strategy. However, even if national policy moves away from
integration, it seems that the momentum of global and European transport policy will ensure
that environmental betterment remains prioritised as a policy objective. While it is now
recognised that the UK, like most developed countries, has a well–developed highway network,
new road construction will be limited, although there will still be some substantial targeted
improvements (see, DETR, 2000e). More resources will be devoted towards the more effective
management of the system, including the achievement of environmental objectives.

2.6.2 Some final conclusions
A consensus has emerged that the environmental impacts of transport are important. Moreover,
environmental policies may not conflict with economic competitiveness because appropriately
designed environmental standards may lead to innovation resulting in a win–win situation
(Porter and Linde, 1995). However, there are still some disagreements about how important
environmental impacts are and what should be done about them. Nash (1997) notes that this is
partly due to the lack of consensus on the principles that should be used in environmental
appraisal, and in particular whether it is appropriate to use “willingness to pay” type measures
or opportunity cost measures based on environmental standards. As Tables 2.9 and 2.10 show
this can result in huge variations in valuations, particularly for climate change. There is also a
similar lack of consensus on the most appropriate measures. Environmental economists would
argue for market–based methods involving pricing, taxes and tradable permits. Ecologists and
32

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

environmental scientists would argue for a standards based approach. Current UK and European
policy appears to involve a mixture of the two measures. However, the important litmus test,
particularly in the UK, will be the extent to which road user charging is adopted. In any event,
particularly outside congested urban areas, it seems likely that there will be continued reliance
on standards based approaches which in turn has important implications for the design,
management and maintenance of transport infrastructure. To use the phraseology of Hyder
Consulting (1999), a considerable amount of work is required if we are to convert old roads into
green roads.
GB £ billion a year in 1994 prices
RCEP (1994)

Newbery

Maddison
and Pearce

Air pollution
Climate change
Noise and vibration

2.0–5.2
1.5–3.1
1.0–4.6

2.8–7.4
0.4
0.6

19.7
0.1
2.6–3.1

Total environmental costs

4.6–12.9

3.8–8.4

22.4–22.9

Road accidents

5.4

4.5–7.5

2.9–9.4

Quantified social and
environmental costs other
than congestion costs

10.0–18.3

8.3–15.9

25.3–32.3

Congestion costs 1

not included

19.1

19.1

Total road transport
Externalities 2

10.0–18.3

27.4–35.0

44.4–51.4

1. The costs of delays to road users and operators and increased running costs at slow speeds
in congested conditions.
2. Not including the costs of damage by vehicles to roads, which both Newbery and Maddison
and Pearce included in the total; the Eighteenth Report showed separately the costs of
providing, maintaining and operating roads.
Source: RCEP, 1997.

Table 2.10: Road Transport: Quantified Environmental and Social Costs.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

33

References
ACTRA, 1977

Report of the Advisory Committee on Trunk Road
Assessment. Chair: Sir George Leitch. HMSO, London.

Adams J, 1993

No Need for Discussion. The Policy is now in Place! In
Stonham, P. (ed) Local Transport Today and Tomorrow. Local
Transport Today, London.
Traffic in Towns . HMSO, London.

Buchanan C et al , 1963
Button KJ, and
Gillingwater D, 1986

Future Transport Policy , Croom Helm, London.

Cm2426, 1994

Sustainable Development: The UK Strategy. HMSO, London

Commission for Integrated
Transport (CfIT), 1999

National Road Traffic Forecasts. Advice by the Commission
for Integrated Transport

Department of Environment,
1990

UK Annual Report. This Common Inheritance. HMSO,
London.

Department of the Environment, T own Centres and Retail Developments. HMSO, London.
1996

34

Department of Environment,
1997

The United Kingdom National Air Quality Strategy.
Cm.3587. The Stationery Office, London.

Department of Transport, 1989

National Road Traffic Forecasts. DoT, London.

Department of Transport, 1993

Design Manual for Roads and Bridges. Volume II –
Environmental Assessment. DoT, London.

Department of Transport, 1996

Transport, the Way Forward. The Government’s Response to
the Great Transport Debate. Cm.3424. HMSO, London.

DETR, 1998a

National Road Traffic Forecasts (Great Britain) 1997.
Working Paper No. 1 Car Ownership: Modelling and
Forecasting and Working Paper No 2 Car Use: Modelling and
Forecasting. DETR, London.

DETR, 1998b

A New Deal for Transport: Better for Everyone. The
Government’s White Paper on the Future of Transport. Cm
3950. The Stationery Office, London

DETR, 1998c

A New Deal for Trunk Roads in England. DETR, London.

DETR, 1998d

A New Deal for Trunk Roads in England: Understanding the
New Approach to Appraisal. DETR, London.

DETR, 1998e

A New Deal for Trunk Roads in England: Guidance on the
New Approach to Appraisal . DETR, London.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

DETR, 1998f

Breaking the Logjam. The Government’s Consultation Paper
on Fighting Traffic Congestion and Pollution through Road
User and Workplace Parking Charges. DETR, London.

DETR, 1999a

From Workhorse to Thoroughbred. A Better Role for Bus
Travel. DETR, London.

DETR, 1999b

Sustainable Distribution: A Strategy . DETR, London.

DETR, 1999c

Accident Investigation Transport Safety Review, Consultation
Paper.

DETR, 1999d

Guidance on Provisional Local Transport Plans . DETR,
London.

DETR, 1999e

Report on the Review of the National Air Quality Strategy.
Proposals to Amend the Strategy.

DETR, 2000a

Tomorrow’s Roads: Safer for Everyone – The Government’s
road safety strategy and casualty reduction targets for 2010.
DETR, London.

DETR, 2000b

New Directions in Speed Management: A review of policy.
DETR, London.

DETR, 2000c

Guidance on Full Transport Plans. DETR, London.

DETR, 2000d

A Good Practice Guide for the Development of Local
Transport Plans. DETR, London.

DETR, 2000e

Transport 2010: The 10 Year Plan. DETR, London.

European Commission, 1992

The Future Development of the Common Transport Policy –
A Global Approach to the Construction of a Community
Framework for Sustainable Mobility. EC, Brussels.

European Commission, 1995

CTP Action Programme 1995–2000. EC Brussels.

European Commission, 1996

The European Auto Oil Programme. Directorate Generals for:
Industry; Energy; and Environment, Civil Protection and
Nuclear Safety. EC, Brussels.

Glaister S, Burnham J,
Stevens H and Travers T,
1998

Transport Policy in Britain. Macmillan, London. (See
particularly Chapter 4 – Making Transport Policy in the
European Union).

Glaister S, 1999

Observations on the New Approach to the Appraisal of Road
Projects. Journal of Transport Economics and Policy, 33, 2,
pp227–234.

Goodwin P, Hallett S, Kenny F
and Stokes G, 1991

Transport: The New Realism . Report to the Rees Jeffreys
Road Fund.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

35

36

Hyder Consulting in
association with the British
Road Federation, 1999

Old Roads to Green Roads. Landor Publishing, London.

The Institution of Highways &
Transportation, 1997

Transport in the Urban Environment. IHT, London.

Local Transport Today, 1998

White Paper Special Issue. Issue 243. 30 July.

Mackie P, 1998

The UK Transport Policy: White Paper. Journal of Transport
Economics and Policy, 32, 3, pp399–404.

Maddison D, Pearce D,
Johansson O, Calthrop E,
Litman T and Verhoef E
1996

Blueprint 5: The True Costs of Road Transport. Earthscan,
London.

Mauch SP and
Rothengatter SW, 1995

External Effects of Transport. UIC, Paris.

Ministry of Transport, 1964

Road Pricing: Economic and Technical Possibilities . HMSO,
London.

MVA in association with the
Institute for Transport Studies,
University of Leeds, David
Simmonds Consultancy,
John Bates Services and
Environmental Resources
Management, 1999

Methodology for Multi–Modal Studies. Guidance Note. Draft
for Consultation. Prepared for DETR. May.

Nash C, 1997

Transport Externalties: Does Monetary Valuation Make
Sense? In de Rus, G. and Nash, C. Recent Developments
in Transport Economics. Ashgate, Aldershot.

Newbery DM, 1995

Royal Commission Report on Transport and the Environment.
Economic Effects of Recommendations. Economic Journal,
pp105.

Peirson J, Skinner I and
Vickerman R, 1994

Estimating the External Costs of UK Passenger Transport: The
First Step Towards an Efficient Transport Market. Discussion
Paper 94/2. Centre for European, Regional and Transport
Economics, University of Kent, Canterbury.

Porter MC and
Linde van der C, 1995

Towards a New Concept of the Environment Competitiveness
Relationship. Journal of Economic Perspectives, 9, 4,
pp97–118.

Preston J, 1999

The Future for Competition and Ownership in European
Transport Industries. Presented to the European Transport
Conference, Robinson College, Cambridge.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Price A, 1999

A New Approach to the Appraisal of Road Projects in
England . Journal of Transport Economics and Policy, 33, 2,
pp221–226.

RCEP, 1994

Eighteenth Report. Transport and the Environment. Cm 2674.
HMSO, London.

RCEP, 1997

Twentieth Report. Transport and the Environment –
Developments since 1994. Cm 3752. HMSO, London.

SACTRA, 1992

Assessing the Environmental Impact of Road Schemes.
HMSO, London.

SACTRA, 1994
UK Round Table on
Sustainable Development,
1996

Trunk Roads and the Generation of Traffic . HMSO, London.
Defining a Sustainable Transport Sector.

Secretary of State for Scotland,
1998

Travel Choices for Scotland . The Scottish Integrated Transport
White Paper. Cm 4010, The Stationery Office, London.

UNCED, 1992

Agenda 21. Rio Earth Summit. Endorsed at UNCED.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

37

38

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

C HAPTER 3. E NVIRONMENTAL M ANAGEMENT S YSTEMS
3.1 Environmental protection and management
In recent years environmental protection has become a central management theme for many
businesses. The degree of commitment to environmental management depends upon the
interaction of an industry with the environment, the nature of its business and the environmental
impact of its activities. The terms, “environmental protection” and “environmental
management” have both been used deliberately in this opening paragraph since they each have
a particular significance. Before progressing any further it is necessary to make a distinction
between the two.
❍ environmental protection recognises that our presence, either as individuals or as
industrial units, inevitably impacts on the environment and often does so in a detrimental
way. Consequently action is necessary to protect aspects of the environment that have
particular significance, intrinsic value or legal protection; and
❍ environmental management acknowledges that we damage the environment by our
actions but providing we manage or control the damage within tolerable limits then it is
acceptable to proceed.
The two concepts of protection and management are not, and should never be, mutually
exclusive. As mentioned in Chapter Two an important concept is that of sustainability, which
using the Brundtland definition means the ability to meet the needs of current generations
without compromising the needs of future generations.
The UK legal system uses what is referred to as the Precautionary Principle to regulate industry
by reversing the burden of proof (Construction Confederation, 1998). Any new product or
process is deemed likely to cause environmental harm unless it can be proven otherwise.
Over the years, the development of the road network across the UK has undoubtedly
contributed significantly to the changing of the landscape. Clearly those involved in all aspects
of the design and construction of roads will be very aware of the, often emotive, issues that
surround this highly visible intrusion into the natural environment. In recent years there have
been many high profile and protracted protests about the construction of new roads, where
environmental protection has been the central theme. Conversely older roads, giving access for
people to enjoy their environment have become an attractive and valued part of the natural
environment, for example the Antrim Coast Road in NI (McAleenan, 1998). So protection and
maintenance of the environment extends beyond the natural to include the built environment.
Ironically engineers may find they have to protect a man-made structure that, at some point in
its history, had been the source of environmental damage (for example, Roman roads, listed
buildings, or ancient burial sites).
While it is accepted that protecting the environment, as it now exists, has to be an integral part
of environmental management there is a need for common–sense practical measures to help
apply the concept to the maintenance of highways. Environmental management takes full
account of the issues, the relevant pollutants and the trade–offs to be considered when
maintaining a balanced environment (Table 3.1).

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

39

Item
Aggregate
Extraction

Activity
Structural maintenance
materials require aggregate
that is generally quarried
locally. This is a non–
renewable resource.

Effect
Adverse

Impact
Moderate

For example, in NI structural
maintenance uses just over
400,000 tonnes of aggregate
per year which is only some
two percent of the annual NI
quarrying output.
Bitumen

Bituminous road making
materials. Bitumen is a
by–product of the petroleum
industry and is therefore a
non–renewable resource.

Comments
Recycling of old pavement layers is already
permitted under the specification. This is at the
contractor’s option but is not frequently used.
Central government may in future decide to
introduce an aggregate extraction tax and that
would encourage more recycling. If not, a more
pro–active approach to increasing the amount
of recycling should be considered
The proposed NI Waste Management Strategy
includes mandatory targets for increased
recycling and reduced waste. This will be an
additional driver for recycled pavement
materials.

Adverse

Small
The only alternative to bituminous mixtures is a
(in terms of total
concrete pavement. While this would be
use of oil products) suitable for major reconstruction schemes
experience tends to favour flexible bituminous
materials.
There may be a small advantage in using
asphalt rather than bituminous macadam.
Asphalt has a higher bitumen content, lasts
longer and does not require bitumen-based
surface dressing every seven years. The
mitigating effect would be marginal.

Energy

Bituminous and concrete
materials require energy for
manufacture and transport to
site.

Adverse

Noise

Positive
More frequent resurfacing
produces smoother surfaces
and means fewer potholes and
uneven reinstatements; this
results in less noise and
vibration.

Small
(in terms of total
energy use)

The adverse environmental impact is very small
in terms of total energy use.

Moderate

A good Structural Maintenance Plan will help
to produce smoother surfaces, with less noise
which benefits people living or working close
to heavily-trafficked roads.

New types of bituminous
pavements are significantly
quieter.

Thin Surfacing and Stone Mastic Asphalt are
relatively new materials that generate much
less traffic noise. Their use may be considered
on routes where traffic noise is a problem,
subject to good durability and long-term
skidding resistance. (Note: An adverse effect of
extending the use of these materials is the
increased volume of high PSV aggregates being
used. A balance will have to be struck).

Ride Quality

More frequent resurfacing
produces smoother surfaces,
fewer potholes and
reinstatements; this reduces
vehicle operating costs.

Positive

Small

A good Structural Maintenance Plan will help
to produce smoother surfaces and consequently
lower vehicle operating costs, but the savings
will be small in terms of total costs.

Safety

More frequent resurfacing
and surface dressing
increases skidding resistance
which reduces skidding
accidents.

Positive

High

A good Structural Maintenance Plan will help
to greatly increase skidding resistance. There
were circa 21500 accidents involving wet
skidding in the UK during 1998. These resulted
in 470 fatalities and over 59,000 injuries. The
social cost of all accidents in that year was
approximately £16,000m. If a structural
maintenance plan prevents just 25% of such
accidents, the associated annual benefits
should cover the increased cost of its
implementation.

Table 3.1: Environmental Impact of Road Maintenance Activities (Examples).
40

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

3.2 Legislation and regulation
The nature of highway maintenance means that engineers must interact with the environment.
Highways have cut through established habitats in order to develop an infrastructure that meets
the needs of the individual, industry, commerce and the nation. Road safety measures such as
street lighting and verge maintenance have an impact on the indigenous flora and fauna. The
highway engineer has to live with the impact that roads have already made on the environment
and to ensure that future actions limit or control any detrimental effects.
There are legal, financial and ethical reasons why an organisation should proceed towards
structured or formal environmental management.
Environmental legislation, whether international, European or domestically driven, changes and
extends as awareness of the environmental impact of human development activities increases.
There are many inter-related pieces of environmental legislation introduced in the UK to give
effect to international treaties, European Union (EU) directives or national concerns. Examples are
the Environmental Protection Act 1990, the Environment Act 1995, Control of Major Accident
Hazards (COMAH) 1999, the Water Resources Act 1991 and The Road Traffic Act 1972.
Additionally, UK planning regulations require formal environmental impact assessments (EIA)
for certain types of proposed development and an environmental statement prepared to
accompany the planning application. The types of project included are motorway construction,
privately financed toll roads and coastal protection schemes. Motorways are subject to
compulsory environmental assessment. Modifications to motorways are included if the size and
nature is such as to significantly impact on the environment. The legislation covering when an
EIA is required for a road scheme is embodied in European Community Council Directive
85/337/EC subsequently amended by Council Directive 97/11. The statutory instrument which
transposes Directive 85/337/EEC and amendment 97/11 into highways legislation is the
Highways (Assessment of Environmental Effects) Regulations 1999.
Under the Highways (Assessment of Environmental Effects Regulations) 1999 any project for
constructing or improving a road will be subject to an EIA where the area of the completed
works together with any area occupied during the period of construction or improvement
exceeds one hectare or where any such area is situated in whole or part within a sensitive area.
The legislation defines “sensitive area”' to include, amongst others, Sites of Special Scientific
Interest, National Parks and Areas of Outstanding Natural Beauty.
Under Directive 97/11 a system is also in place to issue “Notices of Determination”, including,
where the determination is not to undertake an EIA, detailed reasons why.
The legislation only applies to construction and improvement. Maintenance and minor network
modifications are normally excluded.
There are many instances where the highway engineer needs to ensure compliance with
environmental legislation. Clearly, in this constantly changing field there needs to be a system
that ensures that the organisation keeps abreast of and continually adheres to their regulatory
obligations.
Non–compliance with environmental legislation brings with it the likelihood of prosecution and
financial penalty. There are many documented cases where the Environment Agency has
brought prosecutions against individuals, private companies, and the public sector for breaches
of the Environmental Protection Act 1990 or the Water Resources Act 1991 (Prosecutions
Review, 1997; 1998).
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

41

The UK Environment Agency’s (UKEA) enforcement and prosecution policy (UKEA, 1998), sets
out the principles to be followed across all areas regulated by the Agency. It lists the
circumstances in which the Agency will normally expect to prosecute. These include;
❍ incidents or breaches of the law which have or could have significant consequences for
the environment;
❍ carrying out operations without a relevant licence;
❍ excessive or persistent breaches of regulatory requirements;
❍ failure to comply or to comply adequately with formal remedial requirements, and
❍ reckless disregard for management or quality standards.
It is the UKEA’s usual practice to take action against an organisation where the offence results
from the organisation’s activities. However, their policy also recognises that poor environmental
practice is primarily a management responsibility. The UKEA acknowledges, therefore, that as
well as taking action against companies, it will also consider any part played by individual
officers of a company, including its directors, managers and the company secretary. It will take
action against them if the offence was committed with their consent, was due to their neglect
or “turning a blind eye” to what was happening.
Examples of penalties presently available (1999) to the courts for certain environmental offences
are:
❍ Magistrates’ Courts; up to six months imprisonment and/or £20,000 fine.
❍ Crown Court: up to five years imprisonment and/or an unlimited fine.
The cost of defending the prosecution, including legal defence teams, expert witnesses, staff
time and court costs will add considerably to the cost of non–compliance. The cost of
developing and implementing a clear and concise environmental management system that suits
the organisation’s management style is negligible by comparison.
English Nature and English Heritage (and their equivalent in Northern Ireland, Scotland and
Wales) will need to be consulted in relevant cases. Water authorities will need to be consulted
on relevant drainage matters.
The ethical argument for environmental management is presented in the UN Principles on
Environment and Development 1992 (Box 3.1).
The right to make use of the environment to the best advantage of all citizens comes with the
responsibility to ensure that the environment survives to benefit future generations – the
principal of sustainable development.

3.3 Organisational considerations
Environmental management is not a new phenomenon but applying a systematic approach to it
is. It is only relatively recently that international standards for environmental management were
developed and with that the stimulus for management frameworks to deal with them (Cascio et
al, 1996). An environmental management system (EMS) provides the structure for a company to
effectively manage its environmental performance in a systematic, pro–active, and “continually
improving” way.
There are many questions that come to the surface when considering a change of direction
within an organisation. The highway engineer, in the role of developer/ implementer of an EMS
will be required to justify the need for an EMS and to persuade the chief officer of a local
authority or immediate director to invest time and money on the project.
42

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Box 3.1: The UN Principles on Environment and Development (1992).
Principle 1.

Human beings are at the centre of concerns for sustainable development. They are
entitled to a healthy and productive life in harmony with nature.

Principle 2.

States have, in accordance with the Charter of the United Nations and the principles
of international law, the sovereign right to exploit their own environmental and
developmental policies, and the responsibility to ensure that activities within their
jurisdiction or control do not cause damage to the environment of other States or of
areas beyond the limits of national jurisdiction.

Principle 3.

The right to development must be fulfilled so as to equitably meet developmental and
environmental needs of present and future generations.

Principle 4.

In order to achieve sustainable development, environmental protection shall
constitute an integral part of the development process and cannot be considered in
isolation from it.

Principle 5.

All States and all people shall co–operate in the essential task of eradicating poverty
as an indispensable requirement for sustainable development, in order to decrease the
disparities in standards of living and better meet the needs of the majority of the
people of the world.

Principle 6.

The special situation and needs of developing countries, particularly the least
developed and those most environmentally vulnerable, shall be given special priority.
International actions in the field of environment and development should also address
the interest and needs of all countries.

Principle 7.

States shall co-operate in a spirit of global partnership to conserve, protect and restore
the health and integrity of the Earth’s ecosystem. In view of the different contributions
to global environmental degradation, States have common but differentiated
responsibilities. The developed countries acknowledge the responsibility that they
bear in the international pursuit of sustainable development in view of the pressures
their societies place on the global environment and of the technologies and financial
resources they command.

Principle 8.

To achieve sustainable development and a high quality of life for all people, States
should reduce and eliminate unsustainable patterns of production and consumption
and promote appropriate demographic policies.

Principle 9.

States should co–operate to strengthen endogenous capacity-building for sustainable
development by improving scientific understanding through exchanges of scientific
and technological knowledge, an by enhancing the development, adaptation,
diffusion and transfer of technologies, including new and innovative technologies.

Principle 10.

Environmental issues are best handled with the participation of all concerned citizens,
at the relevant level. At the national level, each individual shall have appropriate
access to information concerning the environment that is held by public authorities,
including information on hazardous materials and activities in their communities, and
the opportunity to participate in decision–making processes. States shall facilitate and
encourage public awareness and participation by making information widely
available. Effective access to judicial and administrative proceedings, including
redress and remedy, shall be provided.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

43

It is unlikely that any individual or organisation could claim to conduct its business without
harm or impact on the environment, therefore it is important that the situation is managed to
mitigate negative environmental impact. As the force behind environmental management within
a road authority the highway engineer must wear the consultant’s hat and market environmental
management as a product that the chief officer cannot be without.
Environmental issues are not new to senior management. Local Authorities are committed to the
fulfilment of Local Agenda 21 while sustainable transportation is high on the UK government’s list
of priorities. Examples of performance indicators for current environmental initiatives may include:
❍
❍
❍
❍

plans in place to meet Local Agenda 21 objectives;
sustainability indicators developed and agreed;
increased availability and easier access to public transport, and
increase in the calculated life of the public roads network.

The key questions that senior management should be considering are:
1. How will the organisation benefit from implementing an environmental management system?
Developing and operating an EMS is a sure way of confirming that environmental commitments
are being met and that there is a structured method in place to deal with non–conformances. If
it is properly designed at the outset and correctly operated throughout the organisation then
senior management can be assured that their activities comply with environmental legislation
and meet mainstream public expectations.
2. How much is it going to cost?
It is not always possible to put an exact cost on such a project since much of this will depend
on how complex the developed EMS becomes. Senior managers need a clear and concise EMS,
that fits with current management thinking and gives consideration to the broad range of
environmental risks that might arise. Stay with the key environmental risks. An EMS will make
more sense if it focuses on the big issues (the risk of polluting a watercourse) rather than the
minutiae (disposal of empty typing fluid bottles?), and the costs are much more acceptable.
Before a presentation of the EMS to the chief officer and members of the board a preliminary
estimate of the cost of developing an EMS should be undertaken and compared with estimated
annual financial liabilities. This should allow a demonstration of the costs and benefits of
proceeding. By way of comparison, a roads authority introduced a completely new safety
management system, loosely based on the requirements of ISO 9001 (McAleenan and Orr,
1999). The total costs including R&D, production, and staff development was in the order of
£75k. This figure was easily justified when compared to the estimated annual financial
liabilities of £1.1m.
3. Will it save us any money?
Consider the likely financial penalties for non–compliance with statutory obligations and
couple them with the defence costs associated with any criminal or civil action. For public
sector organisations this is a misuse of “tax payers” money while for private business profits are
seriously affected.
4. How much staff time will be involved?
This will depend on the approach adopted but as a minimum a project champion, with all the
necessary management and systems skills, should be able to produce an organisation specific
EMS in a matter of months. This will require input from operational staff and environmental
specialists, although the input will be intermittent and not particularly onerous.
44

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

A properly constructed EMS will clearly identify the level of management responsibility
necessary for the successful operation of the system. The architect of the system must endeavour
to integrate specific tasks closely with current management responsibilities. Involving those
who will operate the system in its development will increase the level of “buy–in” when the
EMS is launched.
5. What are the training implications?
It will be essential to give staff an overview of the EMS and to promote ongoing commitment to
environmental management. The extent and method of delivery of this training will depend on
how the EMS has been developed. The EMS must also identify areas of specialist training and
EMS developers should be aware of the need to keep this to the optimum.
6. Is it acceptable to the public? (of particular relevance to local authorities)
Protecting the environment has become a mainstream issue for the public. Awareness of the
issues has increased greatly over recent years and with it the level of tolerance of pollution or
environmental damage has decreased. Whilst people might be united under the environmental
banner to oppose a particular project their reasons for doing so cannot be generalised. Some
protestors, opposing a road realignment, will be fighting to protect a rare species of flora or
fauna. Others will be concerned to protect an established way of life or the value of their
property. All concerns are legitimate, and rather than being confrontational, it will be better to
show commitment to protecting the environment through consultation and environmental
management, where necessary.
7. How does it fit with sustainable policy objectives?
Environmental legislation and government policy seeks to achieve sustainable development.
The UN Principles on Environment and Development speak of the right to develop and the
obligation to protect the environment for future generations. Business activities need to be
managed in a way that gives environmental concerns their proper place, alongside key
management issues. This will ensure the protection of the environment and the elimination,
reduction or control of the amount of environmental damage caused.
8. Where does it fit with best value principles?
Best value seeks to ensure that the views of an organisation’s stakeholders are considered as part
of the business planning process. Stakeholders, through the best value program, are likely to
identify some, if not many, environmental concerns that they expect to be resolved. In the
absence of a strategic approach to such demands organisations could find they are being pushed
from one high profile environmental issue to another (fad chasing). Using the EMS, particularly
environmental risk management, an organisation can demonstrate, to its stakeholders, that it is
tackling environmental issues in a structured and reasonable fashion. The best value program
permeates all of an organisation’s activities on a five–year cyclical basis. The EMS should be a
fundamental factor in any review of services undertaken by an organisation.
There will be other questions that arise as the process develops, however if the reasoning
expressed above is accepted there is every chance that the production of an EMS will proceed.

3.4 Key considerations
Many comparisons have been made between quality and environmental management systems.
Quality management systems exist to provide organisations and third parties with assurance of
adherence to procedures and specifications through a structured, verifiable management
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

45

system. Similarly the operation of a systematic approach to managing environmental
performance will clearly demonstrate a commitment to meeting environmental objectives in a
manner that can be corroborated (Rothery, 1995). ISO 14001 – the EMS standard – is not
designed to achieve a particular level of performance but, through its use, organisations can be
assured they are meeting their legal obligations and that environmental incidents are limited or
avoided completely.
An environmental management framework includes matrices that:
❍ match activities with the environmental impacts (Figure 3.1);
❍ match environmental impacts with the legislative requirements (Figure 3.2), and
❍ identify cause, effect and control (Figure 3.3).
All of these areas need to be investigated and the implications understood before systems,
procedures and documentation are developed to help the organisation deal with them.
Ultimately the framework will be detailed in a management manual, incorporating the policy
and arrangements for planning, implementing, auditing and reviewing the environmental
management system. It is this process that will allow organisations to consider systematically all
the environmental aspects in the context of their existing overall management system and
culture. An environmental management system has more chance of being embraced by the
whole organisation if it develops naturally in line with established business objectives rather
than being produced in haste in order to satisfy the certification criteria of some standard. That
is not to suggest that there is a problem with seeking recognition, rather that it would be better
if recognition was a welcome “spin–off”.
Environmental concern has moved from being an issue for the eccentric few to one that is a key
question for the informed majority in the industrialised world. It must compete with many other
management issues because in an increasingly competitive world the operation of private and
public sector organisations has to make sound commercial sense. Therefore it is important to
integrate environmental management with all other aspects of the business.
The UK is faced with many environmental legislative and regulatory requirements that continue
to develop and grow as our collective knowledge of environmental issues expands. The
development of an environmental management framework provides a means for organisations
to maintain an awareness of current and projected legislation. Normally the development of
environmental regulation will come from European Union directives, translated into national
legislation by the parliaments of the EU Member States.
Environmental laws and regulations are numerous and increasing. Enforcement responsibility
falls to a number of Agencies, such as the UK’s Environment Agency, the Scottish Environment
Protection Agency (SEPA) and Department of Environment (NI) Environment and Heritage
Service. Beyond the UK there is the European Environment Agency, a body established to
supervise environmental data gathering within the EU.
With legislation, increasing environmental awareness in the marketplace, and high customer
expectations the time is right for senior management to make a commitment to managing
environmental issues.

3.5 Delivering good environmental practice
Good environmental practice needs to be presented in a structured and verifiable manner, to an
internationally recognised standard. Given the nature of environmental management a flexible
system is required that will cope with the growth in the knowledge of environmental cause and
effect as well as the need to continually improve the process. Crognale (1999) reported that the
46

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Affected by highway maintenance activity
Highway
maintenance
activity

Air
Quality

Vehicle driving
Vehicle maintenance
Machinery operating
Cable laying
Drainage
Pavement repair
Hedge/ tree trimming
Weed control
Verge maintenance
Painting street
furniture
White lining
Transporting, using
and storing
substances
Winter service
Street lighting

●

Water
course

Landscape

Built
Environment

Ecology

Energy

Noise

●

●

●

●

●

●

●

●

●

●

●

●

●

●

●

●

●
●

●

●

●

●

●

●

●
●

●

●

●
●

●

●

●

●

●

●

●

●

●

●

Example only. There may be other activities to be added or other effects to be considered.

Figure 3.1: Match activities with the environmental impacts.

new way of thinking about the environment is compelling organisations to take stock of their
environmental performance, creating a desire to do the right thing, rather than to live with the
consequence of errors.
An EMS is the vehicle for delivering sound environmental practice but the design of the system
must be adapted to suit the needs of a particular industry or public sector activity. In this context
it must be remembered that highways maintenance engineers can only manage those aspects of
the environment over which they exert a controlling influence. Therefore, global issues such as
tropical deforestation and ozone depletion, important though they are, are not for discussion in
this chapter.
An EMS developed for a highway maintenance organisation will focus on issues such as
environmental noise, air quality, watercourse pollution, recycling, wildlife protection, energy
efficiency and protection of the natural and built heritage. Good environmental practice can
only be established by examining the:
❍
❍
❍
❍

risks;
root causes and effects;
controls, and
links between the various risks.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

47

Highway maintenance activity

Effect

Current Position

Related legislation

Vehicle maintenance

Air quality

Refer to
environmental policy

Environmental Protection
Act 1990

Ecology

Refer to environmental
work practices manual

Environment Act 1995
Clean Air Act 1993

Energy

Key business objective

Wildlife and Countryside
Act 1981

Noise

No action planned

Figure 3.2: Match environmental impacts with the legislative requirements .
It is important in any such study that legal compliances and best practice are considered in
determining levels and methods of control. Also there will be many environmental effects
closely linked to the use of highways over which the highway engineer has no direct control,
such as vehicle exhaust emissions, energy efficiency at source and traffic volumes. In these
cases the response should be to identify the source of control and take whatever measures are
open to influence the decision makers.

3.6 The environmental management framework
Any framework developed for the purpose of environmental management must:
❍
❍
❍
❍

identify the environmental impacts to be controlled;
help to co–ordinate the various activities associated with managing the highways;
introduce good environmental practice on the ground, and
incorporate the concept of continual improvement.

When managing the environment, the engineer will be faced with many uncertainties about
which predictions have to be made. Actions taken to mitigate environmental impact in one
respect could have a counter effect on another. For example thin surfacings and stone mastic
asphalt have a positive benefit in areas where traffic noise is a significant problem but these
materials require more non–renewable high PSV aggregates than hot–rolled asphalt (Orr and
Crilly, 1998). Also actions taken to protect or enhance the environment for one species could
have a detrimental effect on another.
The key to success will be maintaining a balance between each of the influences, recognising
that at times different influences will have prominence. It is this balance or trade–off that is
challenging and there will be times when the engineers will need specialist advice, particularly
when faced with critical environmental decisions. Although the highway engineer will have to
wrestle with these issues, many of them have been addressed already. Among other things the
environmental legislation deals with waste management, protection of species, habitats and
parts of the built environment.
Whatever method is chosen to pursue environmental management it must fit with the
organisational vision and integrate with national policy. The DETR’s guidance on a New
Approach to Appraisal (NATA) is a case in point (see also section 2.4.2 and Tables 2.1 and 2.2
in Chapter Two). The approach includes the identification and assessment of problems and the
options for resolving them. The approach taken throughout the process is to work within the five
objectives of accessibility, safety, economy, environment and integration (Box 3.2).
48

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Figure 3.3: Cause, effect and control.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

49

Environmental Risk Assessment

What needs to be controlled

Source of Pollution

Highway Maintenance Activity

Direct
or
Indirect

High or Low
significance

Controls

Effect

Cause

List the control measures

Environmental effect

High or Low
significance

Older roads have become an attractive and valued part of the natural environment – the Antrim Coast Road,
Northern Ireland.
3.6.1 Choosing a standard
There was a time when the environmental practitioner had three standards to choose from;
British Standard BS 7750, Europe’s Eco–Management and Audit Scheme Regulation (EMAS) and
ISO 14000. While BS 7750 and EMAS are both process and performance–orientated, ISO 14000
standards are limited to process–type management standards. BS 7750, which had a
considerable influence on the development of ISO 14000 standards, is no longer applicable.
EMAS, designed to fulfil the regulatory objectives within the European Union, exceeds the scope
of the international ISO committee (TC207) tasked with drafting the ISO 14000 standards. The
debate on bringing EMAS and ISO 14000 into alignment has continued for some time with

Box 3.2: The UK Government’s Overarching Objectives for Transport.
❍ To protect and enhance the built and natural environment.
❍ To improve safety for all travellers.
❍ To contribute to an efficient economy, and to support sustainable economic growth in appropriate
locations.
❍ To promote accessibility to everyday facilities for all, especially those without a car.
❍ To promote the integration of all forms of transport and land use planning, leading to a better, more
efficient transport system.
Source: DETR, 1998.

50

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

ISO 14001

EMAS

Type of Standard

Voluntary

Voluntary, EU Regulation

Applicability

1. Activities, products and services.
2. Whole organisation or part of it

1. EU
2. Individual facilities and
industrial activities

Focus

Process orientated

Process and performance
orientated

Policy Commitment

1. Continual improvement of EMS,
2. prevention of pollution,
3. compliance with applicable
legislation, and
4. compliance with voluntary
commitments

1. Continuous
improvement of
environmental
performance, and

Audits

1. EMS, and
2. Monitoring and measuring key
environmental characteristics.
3. Frequency not specified

1. EMS.
2. Processes data, and
3. Environmental
performance
4. Every three years

Public communication

1. Environmental policy

1.
2.
3.
4.

2. Compliance with
applicable legislation

Environmental policy.
Programme
EMS
Environmental
statement
5. Annual performance
data

Table 3.2: Comparison of ISO 14000 Standards and EMAS.

non–Europeans arguing that ISO 14000 is intended to complement national regulatory regimes
not replace them. Many exponents of ISO 14000 view national regulation as unnecessary and
believe that EMAS, if implemented, could present a barrier to trade. This would be particularly
true for developing countries should international environmental performance standards be set
at unattainable levels.
EMAS applies to individual facilities or specific industrial activities whereas ISO 14000
standards are applicable to an organisation’s activities, products and services. Since the
introduction of either the ISO 14000 standards or EMAS is voluntary the practitioner, when
considering which path to follow, should consider carefully the consequences for their
organisation. The EMAS route is much more onerous (Table 3.2) in that its audits are more
widespread and there is a greater degree of public consultation required.
The solution is to use ISO 14000 standards as the initial basis for developing the organisation's
EMS. If the organisation desires it, or the EU demands it, then additional performance–orientated
standards can be added to the ISO 14000 standards to satisfy the EMAS criteria.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

51

The nature of highway maintenance means that engineers must interact with the environment.

3.7 The ISO 14001 Standard
The ISO 14000 standards provide organisations with the tools and systems for the effective
management of their various environmental obligations without prescribing the goals to be
achieved (Table 3.3). The standards aim to provide guidance for the development of a
comprehensive approach to environmental management that integrates with an organisation's
values and beliefs (Whitelaw, 1997).
There are numerous documents in the ISO 14000 series each having value and each
interconnected in some way. The standards cover the organisation (management systems
auditing and performance evaluation) and the product (product standards, labelling and life
cycle assessment). Product evaluation standards are not necessary to become registered to ISO
14001, however environmental practitioners should find they are useful tools. The many
elements within the ISO 14000 series of standards include:

3.7.1 Organisational evaluation standards
1. Environmental management system (EMS). Designed to provide a structured and systematic
approach to overall environmental management. It covers policy, procedures, stakeholders,
responsibilities and audit mechanisms. (Box 3.3).
52

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Number

Title

ISO 14001:1996

Environmental Management Systems – Specification with Guidance
for Use
Environmental Management Systems
Environmental Management Systems – General Guidelines on
Principles, Systems and Supporting Techniques
Guidelines for Environmental Auditing
Guidelines for Environmental Auditing – Audit Procedures –
Auditing of Environmental Management Systems
Guidelines for Environmental Auditing – Qualification Criteria for
Environmental Auditors
Initial reviews
Environmental Site Assessments
Environmental Labels and Declarations
Environmental Labels and Declarations – Environmental Labelling –
Self Declaration Environmental Claims – Terms and Definitions
Environmental Labels and Declarations – Environmental Labelling –
Self Declaration Environmental Claims – Symbols
Environmental Labels and Declarations – Environmental Labelling –
Self Declaration Environmental Claims – Testing and Verification
Methodologies
Environmental Labels and Declarations – Environmental Labelling –
Type I – Guiding Principles and Procedures
Environmental Labels and Declarations – Environmental Labelling –
Type III – Guiding Principles and Procedures
Environmental Performance Evaluation – Guidelines
Life Cycle Assessment – Principles and Framework
Life Cycle Assessment – Life Cycle Inventory Analysis
Life Cycle Assessment – Impact Assessment
Life Cycle Assessment – Interpretation
Environmental Management – Terms and Definitions

ISO 14002
ISO 14004:1996
ISO 14010:1996
ISO 14011:1996
ISO 14012:1996
ISO
ISO
ISO
ISO

14014
14015
14020
14021

ISO 14022
ISO 14023

ISO 14024
ISO 14025
ISO
ISO
ISO
ISO
ISO
ISO

14031
14040
14041
14042
14043
14050

Table 3.3: ISO 14000 Series of Standards.
Some of the above standards have not yet been published (1999).

2. Environmental auditing (EA). A systematic, documented and verifiable process designed to
ascertain whether the EMS helps the organisation to meet the required standards of
environmental performance, fulfil its legal obligations and achieve what it claims to be
achieving.
3. Environmental performance evaluation (EPE). This is a measure of how well the organisation
is performing in areas such as recycling, pollution prevention and adherence to regulatory
requirements.

3.7.2 Product evaluation standards
1. Environmental aspects in product standards (EAPS). Guides specification writers to take
account of the positive and negative environmental consequences when developing product
standards and if necessary to seek expert assistance.
2. Environmental labelling (EL). Used to provide consistent information about the product
characteristics.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

53

Box 3.3: EMS Manual Contents, Layout and Action List.
Manual Contents should include;
Section 1

General Information
a Description of organisation
b Manual distribution arrangements
c Arrangements for control and revision of documents

Section 2

Policy
a Environmental policy statement
b Key groupings - policy makers (Boardroom), planners (senior/ middle managers) and
implementers (all staff)
c Key tasks and major outputs for each grouping

Section 3

Planning
a Environmental aspects of highway maintenance
b Register of relevant regulations
c Objectives and targets

Section 4

Implementation
a Dissemination of information
b Training arrangements
c Communication arrangements
d Specific environmental management procedures (see sample layout below)
e Emergency response arrangements

Section 5

Monitoring and Auditing
a Performance measures
b Monitoring arrangements
c Corrective and preventive action
d Records
e Audit protocol

Section 6

Management review

Sample Procedures layout
Title
Purpose
Scope
Definitions
Procedures
Responsibility
Documentation
References

Explains why the procedure is necessary and should be followed
Identifies which areas of organisation are affected by the procedure
Explains any necessary technical terms
This section contains the substance of the procedure (use short, numbered, paragraphs with
sub–titling). If appropriate, this section may be drafted using charts, graphs etc.
Identifies the staff of staff grouping responsible for each particular task.
Identifies forms, ledgers etc which will prove compliance with the procedure.
Indicates related procedures, instructions and guidelines (including Regulations and Codes of
Practice).

EMS Development Action List (example)
Dealt with
Policy
Register of regulations
Preparatory review
Tasks and outputs
Environmental aspects
Objectives and targets
Environmental manual
Documentation

54

✔
✔
✔

Planned

Not addressed

Sample
✔
✔
✔

✔
✔

Current position
In business plan
Completed
Completed
In development
Under review
In development
With the Board
Later

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

3. Life cycle assessment (LCA). Used to evaluate the environmental impact of all aspects of a
product; its materials, method of manufacture, use, disposal and other applicable elements.
The most significant of the series is ISO 14001 entitled “Environmental Management Systems –
Specification with Guidance for Use” (Box 3.4). Organisations that want their environmental
management system to be recognised, as conforming to an international standard, will be
assessed against this standard. The remainder of this chapter will concentrate on the
development of an EMS with reference to each of the other evaluation standards where they
have an effect.

3.8 Building an EMS
The first step in the process is gaining top management commitment. Management need to
understand the benefits of an EMS and what it will take to put it in place. Their commitment and
vision has to be clear and communicated across the organisation.
The appointment of a project champion is critical, although not every small or medium–size
organisation will have a large pool of candidates to choose from. The champion should have
the necessary authority, an understanding of the organisation, and project management skills.
The champion should be a “systems thinker” (some ISO 9001, quality management experience
would be a benefit, but not a necessity) and must have the time to commit to developing the
EMS (Hunt and Johnson, 1995).
The project champion should prepare a preliminary budget and activity plan for developing the
EMS. Costs will likely include staff time, training, some consulting assistance, materials, and
possibly some equipment.

Continual

Envir
Mana
gem
Revie ent
w

onme
Polic ntal
y

Plann
Chec
Corre king and
ctive
Actio
n

ing

Imple

ment
a
Oper tion and
ation

Box 3.4: Environmental management system model for the ISO 14001 International Standard.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

55

A team, with representation from managers and those who actually do the work on the ground,
should be convened to identify and assess issues, opportunities, and existing processes. It may
be appropriate to consider including contractors, suppliers, and other external parties in the
team, particularly in a partnering environment. This team will need to meet frequently,
especially in the early stages of the project. A cross–functional team can help to ensure that
reasonable procedures are developed and engender commitment to the EMS.
Employees are a great source of knowledge on environmental and health & safety issues related
to their own work areas as well as on the effectiveness of current processes and procedures.
They can help the project team in drafting procedures. Employee ownership of the EMS will be
greatly enhanced by meaningful employee involvement in the EMS development process.
The next step is to conduct an initial review of the organisation’s current environmental
arrangements and compare these to the criteria for the EMS (ISO 14001). Evaluate the
organisation’s structure, its policies and procedures, training programs, and other factors to
determine which elements may need additional work. The review should identify opportunities,
such as waste minimisation, and help the organisation to set its environmental objectives. It
should also identify any ongoing work to lessen environmental impact, for example, standing

Roads have cut through established habitats.

56

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

arrangements concerning the
use
of
weedkillers
and
instructions regarding the
timing of hedge cutting.
The activity plan may need to
be modified based on the
results of the initial review. The
modified plan should describe
in detail:
❍ the key actions needed;
❍ who will be responsible;
❍ what resources are
needed, and
❍ when the work will be
completed.
At this point the development
of
the
environmental
procedures and the system
documentation should take
place. This might involve
modifying
existing
environmental procedures or
adapting
other
business
procedures, such as quality or
health & safety management
procedures, for EMS purposes.
In some cases, new procedures
may need to be developed.
Remember the benefits to be
gained from using other
employees
and
a
cross–functional team, as
discussed above.
When building an
sure that the
sufficiently flexible
it must be changed

A 19th Century roadbuilders contribution to today’s
environment. Near Stanocum Co Antrim (NI).

EMS make
system is
to allow modification over time. Try to avoid making the EMS so rigid that
frequently to reflect the realities of your activities.

The EMS can be implemented once the procedures and other documents have been prepared.
As a first step, provide the employees with training on the EMS, especially with regard to:
❍ the environmental impacts of their activities;
❍ any new or modified procedures; and
❍ any new responsibilities.
After the EMS is operational, and following a sufficient “bedding in” period, the system
performance should be assessed. This can be accomplished through periodic EMS audits and
ongoing monitoring and measurement. EMS performance assessment gives an organisation the
opportunity to ascertain whether the EMS helps it to meet the required standards of
environmental performance, fulfil its legal obligations and achieve what it claims to be
achieving. It should also be looked upon as an opportunity to identify any weaknesses in the
system and to make any necessary improvements.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

57

3.9 The highways environmental management model
Using a framework, based on the ISO 14000 standards, a simple yet flexible model is presented
in this chapter, incorporating checklists, matrices and tables that acquaint the highway engineer
with the options. This in turn should help the decision making process.
Engineers maintaining and operating highways have many environmental issues to consider,
such as the timing of hedge maintenance to avoid the “bird nesting” season, dealing with
tunnels made by badgers, light pollution or addressing road noise complaints. Sometimes the
issues can conflict and steps need to be taken to avoid or minimise the level of conflict. For
example, trees and hedges need to be trimmed to take account of traffic and road safety but this
can damage the bird's habitat. The answer is to schedule the work for the February to
mid–March period, which allows the hedges to provide winter food and shelter but avoids the
bird nesting season from late March to mid–September. On the other hand taking action to
minimise light pollution could have the beneficial effect of reducing energy consumption.
In order to successfully address environmental protection and management it is necessary to
develop a systematic approach. It will be most effective when the principle of keeping things
simple is adhered to. That can be achieved through environmental risk management.
Historically environmental issues have either been dealt with reactively or at the other extreme
by deeming all products and processes to be potentially harmful to the environment unless

Highways Environmental Model

Environmental Risk
Assessment

Environmental
Management Systems
(EMS)

Learn & Improve

What can cause environmental damage?
What is being done about it?
Is it enough?

What needs to be done?
Who is responsible?
Is it being done?

What could go wrong?
How could it happen?
What can we learn?

Figure 3.4: Highways Environmental Model.

58

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

proven otherwise. The time is right for the issues to be proactively managed within a structure
that can be independently verified. Risks need to be managed in health & safety, likewise there
are environmental risks that need to be addressed. Therefore it is possible to develop a model
for highways environmental management (Figure 3.4), similar to safety management, using a
“three stage” approach as follows:
Stage 1.
Stage 2.
Stage 3.

Know the environmental risks.
Manage the environmental risks
Learn and improve.

3.9.1 Stage 1: Know the environmental risks
There are three questions that help to ascertain what the environmental risks are. These
questions form the basis of environmental risk assessment and although simple in style they are
probing in nature. The answers will invariably lead to a heightened awareness of the issues and
assist in developing management solutions.
The questions are:
1. Which activities could cause environmental damage?
2. What is being done about it?
3. Is it enough?
These questions are extremely powerful. Any good environmental management system,
including the ISO 14001 process, relies on quality information. It is easy to be swayed by the
issue of the day and to demonstrate how well an organisation is geared to deal with it. However
the danger is that this will not achieve the desirable position of properly managing
environmental matters, alongside the other equally important business areas.
An organisation’s environmental policy must reflect the nature, scale and environmental impact
of its activities. Therefore it is acceptable to customise the environmental policy to fit the needs
of the organisation. This can be achieved by a thorough examination of the present position
using the above questions.
The first question, “which activities could cause environmental damage?”, prompts the
organisation to examine what it does and what affect it has on its surroundings, regardless of the
regulatory position. This is always a good starting point in environmental and in safety
management since it allows the organisation to deal properly with current legislation and
prepare for future requirements. Depending on the nature and the scale of the project it may be
necessary to carry out a formal environmental impact assessment. Similarly the follow on
question, “what is being done about it?”, provides the opportunity to detail the actions being
taken to mitigate environmental damage. In essence, having answered the first two questions,
an environmental risk assessment will have been carried out. The opportunity should then be
taken to check for legal obligations and where practicable, best practice as it relates to specific
environmental factors (for example, recycling road materials). The UKEA has an environmental
information tool on their website that gives guidance on the legislation as well as presenting the
reasons for complying. A non–exhaustive list of current [1999] environmental and related
legislation is included (Box 3.5) to assist in this stage of the process. The list may be modified
to produce the organisation’s own Register of Regulations.
The concept of continual improvement is introduced with the, “is it enough?” question. This is
fundamental to good environmental management since public acceptability, technical
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

59

Box 3.5: Legislation relevant to the environmental management of highways (non–exhaustive list).
National Parks and Access to the Countryside Act 1949
Fisheries Act (NI) 1966
Countryside (Scotland) Act 1967
Forestry Act 1967
Countryside Act 1968
Mines and Quarries (Tips Act) 1969
Town and Country Amenities Act 1974
Control of Pollution Act 1974
Salmon and Freshwater Fisheries Act 1975
Wildlife and Countryside Act 1981
Food and Environment Protection Act 1985
Control of Pollution (Amendment) Act 1989
Town and Country Planning Act 1990
Environmental Protection Act 1990
Water Industry Act 1991
Water Resources Act 1991
Protection of Badgers Act 1992
Clean Air Act 1993
Noise and Statutory Nuisances Act 1993
Radioactive Substances Act 1993
Clean Air Act (NI) 1994
Environment Act 1995
Finance Act 1996
Noise Act 1996
Water Resources (Succession to Licences) Regulations 1969
Control of Noise (Appeals) Regulations 1975
Clean Air (NI) Order 1981
Access to the Countryside (NI) Order 1983
Wildlife (1985 Order)(Commencement) Order (NI) 1985
Town and Country Planning General Development Order 1988
Trade Effluent (Prescribed Processes and Substances) Regulations 1989
Control of Asbestos in the Air Regulations 1990
Control of Pollution (Silage, Slurry and Agricultural Fuel Oil) Regulations 1991
Controlled Waste (Registration of Carriers and Seizure of Vehicles) Regulations 1991
Disposal of Controlled Waste (Exceptions) Regulations 1991
Environmental Protection (Applications, Appeals and Registers) Regulations 1991
Environmental Protection (Authorisation of Processes)(Determination of Periods) Regulations 1991
Environmental Protection (Duty of Care) Regulations 1991
Environmental Protection (Prescribed Processes and Substances) Regulations 1991
Controlled Waste (Registration of Carriers and Seizure of Vehicles) Regulations 1991
Controlled Waste Regulations 1992
Environmental Information Regulations 1992
Town and Country Planning (General Permitted Development) (Scotland) Order 1992
Trade Effluent (Prescribed Processes and Substances) Regulations 1992
Conservation (Natural Habitats etc.) Regulations 1994
Roads (Assessment of Environmental Effects) Regulations (NI) 1994
Transfrontier Shipment of Waste Regulations 1994
Waste Management Licensing Regulations 1994
Statutory Nuisance (Appeals) Regulations 1995
Wildlife (1995 Order) (Commencement) Order (NI) 1995
Carriage of Explosives by Road Regulations 1996
Control of Pollution (Applications, Appeals and Registers) Regulations 1996
Environmental Licences (Suspensions and Revocation) Regulations 1996
Environmental Protection (Controls on Substances that Deplete the Ozone Layer) Regulations 1996
Landfill Tax Regulations 1996
Landfill Tax (Qualifying Material) Order 1996
Special Waste Regulations 1996
Waste Management Regulations 1996
Producer Responsibility Obligations (Packing Waste) Regulations 1997
Town Country Planning (Assessment of Environmental Effects) Regulations 1998
Highways (Assessment of Environmental Effects) Regulations 1999
Control of Accident Major Hazards Regulations 1999

60

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

knowledge and engineering practices are in a state of continual development. For example,
providing bat roosts underneath highway structures may not be needed to mitigate
environmental impact but it will improve the environment and allow the organisation to
increase its environmental “credit balance”. A process for compliance improvement is
illustrated in Figure 3.5 (Crognale, 1999).
By using the above three questions an organisation can readily establish the current state of its
environmental control activities. An environmental risk analysis form has been developed to
assist highway engineers in this process (Figure 3.3). It contains a comprehensive, although not
exhaustive, list of environmental issues pertinent to the industry. It may be used as an aid when
undertaking environmental risk assessments.

3.9.2 Stage 2: Manage the environmental risks
Having established what the environmental risks are the next stage is to put together a
management plan to effectively deal with all the issues raised. Environmental management is
not a task to be assigned to an individual, rather it is an issue that everyone in the organisation
needs to be involved in. The plan or environmental management system must be developed
along these lines. As with Stage 1 there are some basic, yet fundamental, questions to be asked.
1. What needs to be done?
2. Who is responsible for doing it?
3. Is it being done?
For the issue to be taken seriously the organisation needs to be clear about what it is trying to
achieve and that efforts to protect and manage the environment has senior management
commitment and support. Two key appointments will ensure the process gets a good start.
Firstly a senior manager, preferably a member of the Board or a chief officer in local
government, should be appointed with direct responsibility for overseeing the implementation
of policies and procedures. This will send a very powerful message that the organisation sees
environmental management as a core strategic issue. The second key appointment will be
someone to design and produce the management system. Both individuals should have the
necessary vision, knowledge of the issues and the leadership, drive and enthusiasm to see the
implementation through to completion. However these people cannot operate alone. The
process must have input from and be representative of all grades and disciplines across the
organisation if it is to stand any chance of success.
The policy and associated documents need to be clear and concise, spelling out the activity,
what needs to be done, the performance measure and who has the responsibility. Typically, the
procedures are presented in the following style:
❍
❍
❍
❍
❍
❍
❍

Title.
Purpose: Background and objectives.
Scope: Activity, location or persons affected (including members of the public).
Definition: Any necessary technical jargon.
Procedures: Short, numbered, bullet points/ charts or graphs.
Responsibility: Which staff member or staff group has responsibility.
Documentation: Forms, control sheets, performance standards etc. that makes the system
auditable.
❍ References: Related procedures, instructions and guidance.
A sample environmental management procedure is shown in Box 3.3.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

61

Review Environmental
Performance

Modify the
process

No

Do we
conform?

Yes

Could we
improve?

No

Yes

Develop an implementation
plan

Is the
cost–benefit
acceptable?

No

Yes

Implement the
improvement

Figure 3.5: Compliance Improvement Process.

62

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

An essential management function is to ensure that responsibilities are being implemented. This
can be achieved through auditing the environmental management system. The opportunity can
be taken when auditing to examine:
❍ the extent to which the environmental management system helps the organisation meet
the required standards of environmental performance;
❍ the extent to which the organisation is fulfilling its legal obligations; and
❍ the extent to which the organisation is achieving what it claims to be achieving.
The major outcomes from the environmental management system audits should be:
❍ the identification of the strengths and weaknesses of the environmental management
system, and
❍ any recommendations for improvements or future action.

3.9.3 Stage 3: Learn and improve
No management system will be complete unless it is acknowledged that incidents may occur
that lead to a breach of policy or regulatory compliance. This does not mean that failure is
inevitable, but that the management plan must have contingencies built in to deal with
emergencies or non–compliances as they arise or come to light. Specific legislation, such as
Control of Major Accident Hazards Regulations 1999 (COMAH), deliberately blends safety and
environmental control. COMAH was enacted to deal with the risk of catastrophic harm from
potentially ultra–hazardous industrial plants. While this has no direct bearing on the work of the
highway engineer there will always be an indirect involvement if a major chemical spillage, an
emission of high concentrations of toxic gases or a major, rapidly escalating, fire occurs in the
vicinity of the public highway. The authors of safety plans, under the COMAH regulations,
should be discussing the likely impact on the road network if an emergency arises. Other less
dramatic incidents are likely to be of direct concern to highway engineers such as:
❍ spillage of various substances on the carriageways leading to damage of the road surface
and pollution of the watercourse, due to run–off, and
❍ carriageway collapse or damage caused by unusual weather conditions or “creature
features” such as tunnelling by badgers.
It is important to anticipate what could go wrong in the environmental risk assessment process,
which should take care of the foreseeable emergencies. It also provides a systematic approach
for dealing with the unforeseen environmental incidents if they occur. The following questions
will guide and control the investigations:
1. What could go wrong?
2. How could it happen?
3. What can we learn?
As with the previous stages the questions are simple in origin yet powerful in their intent. A
properly conducted investigation leads naturally back to a review of the environmental risk
assessment and potentially a modification of the EMS. The model is structured in a way that
allows the lessons to be learnt as a natural part of the overall process of monitoring, auditing
and reviewing compliance with regulation and environmental policy. However if faced with an
unplanned incident or occurrence the lessons from that must be learnt. In that case the
questions become:
1. What went wrong?
2. How did it happen?
3. How can we ensure it does not happen again?
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

63

3.10 Future trends
It is clear that the issue of managing the environment is not a fad, shortly to disappear. Rather,
it is an international process that has evolved over a number of years to become a mainstream
boardroom topic. The competing issues of quality, safety and environmental management are
likely to merge, either into one integrated approach within an organisation or one integrated
management standard. The first option is the most likely short to medium term outcome with an
integrated management standard, still an ideal, coming some time in the future. At a recent
conference on environment and health (1999) the World Health Organisation (WHO) promoted
a good practice approach to health, environment and safety management. Their approach
advocates building upon existing national structures and already established practices, rather
than inventing entirely new arrangements and structures. This is an approach that has been the
most successful in the past, when it comes to introducing new policies. WHO suggest using
quality management techniques, to develop the environmental and safety management systems
as a means of making best use of limited resources and capitalising on the knowledge, already
existing within an organisation.
Quality and environmental matters are addressed under international standards, while the
development of safety management standards is still in its infancy. If the three areas are to
integrate fully a common understanding of purpose will need to be developed. There is a body
of opinion that argues that the quality standards, ISO 9000, do not represent a complete
management system, concentrating as they do on assurance. More significantly, there are
conceptual, terminological and structural differences in the way each of the existing standards
are presented that needs to be harmonised (Wilson and Bryant, 1997). This is currently (1999)
the subject of international discussion.

64

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

References
Cascio J et al , 1996

ISO 14000 Guide – The New International Environmental
Management Standards. McGraw Hill.

Construction Federation, 1998

Construction Health and Safety Manual. CIP Ltd.

Crognale G (editor), 1999

Environmental Management Strategies – The 21st Century
Perspective. Prentice Hall PTR.

DETR, 1998

A New Deal for Trunk Roads in England: Guidance on the
New Approach to Appraisal. DETR, London.

Environment Agency, 1998

Enforcement and Prosecution Policy Version 1. Environment
Agency.

Hunt, D and Johnson C, 1995

Environmental Management Systems, Principles and
Practice. McGraw Hill.

McAleenan C (editor), 1998

Environmental Handbook. DoE(NI) Roads Service. DoE,
Northern Ireland.

McAleenan C. and Orr D,
1999

Safety – Turning the Event into a Process. (unpublished).

Orr D and Crilly R, 1998

The Road to Everywhere – A Policy Evaluation of Structural
Maintenance of Roads and Footways . DoE (NI) Roads
Service, Northern Ireland.

Prosecutions Review, 1997

Second Edition, Monitor Press Ltd.

Prosecutions Review 3, 1998

Third Edition, Monitor Press Ltd.

Rothery B., 1995

ISO 14000 and ISO 9000. Gower.

Transport Research Laboratory,
1999

Design Guide and Specification for Structural Maintenance
of Highway Pavements by Cold In–situ Recycling.
TRL Research Report No. TRL 386. TRL, Crowthorne.

Whitelaw K, 1997

ISO14001 Environmental System Handbook. Butterworth
Heinemann.

Wilson GA, and Bryant RL,
1997

Environmental Management New Directions for the
Twenty–First Century. UCL Press, London.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

65

Further information and reading
DETR, 1988: Digest of Environmental Statistics, No 20. DETR, London.
DETR, 1988: Highways Economic Note No.1. Valuation of the Benefits of Prevention of Road
Accidents and Casualties. DETR, London.
DETR: Road Accidents Great Britain – The Casualty Report.
DETR, 1993: A Guide to the Eco–management and Audit Scheme for UK Local Government – A
Manual for Environmental Management in Local Government. DETR, London.
Department of Transport, 1993: Design Manual for Roads and Bridges, Volume 10 –
Environmental Design, DoT, London.
Department of Transport, 1993: Design Manual for Roads and Bridges, Volume 11 –
Environmental Assessment, DoT London.
Environment Agency, 1997: Operator and Pollution Risk Appraisal (OPRA) Version 2.
Environment Agency.
Environmental Analysis Co–operative, 1999: Don't forget the Environment – A Guide for
Incorporating Environmental Assessment into Your Project. Institution of Chemical Engineers,
London.
European Commission 1985 and 1997: Directives 85/337/EEC and amendment 97/11. The
assessment of the effects of certain public and private projects on the environment. Council of
the European Communities.
ISO 14001:1996: Environmental Management Systems – Specification with Guidance for Use.
The Institution of Highways & Transportation, 1997: Transport in the Urban Environment. IHT,
London.
Stapleton, PJ, 1996: Environmental Management Systems: An Implementation Guide for Small
and Medium–sized Organizations. NSF International.
Turner, S, and Morrow, K, 1997: Northern Ireland Environmental Law. Gill & Macmillan Ltd.
Waite, A, 1997: Environmental Law Handbook, 2nd Edition. Butterworths.

66

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

C HAPTER 4. D RAINAGE , R UNOFF AND G ROUNDWATER
4.1 Introduction
The construction of impervious highway surfaces and any associated hard shoulders, gutter and
pavement areas, can lead to extensive modification of the hydrological cycle with larger
volumes of rainfall–runoff being conveyed over shorter periods of time at increased flow rates
to adjacent surface waters and groundwaters. The runoff regime associated with these
discharges is characterised by episodic, pulsed-flow events which can lead to acute, shock
effects in both hydraulic and water quality terms. The design of highway drainage in the UK has
traditionally provided for the rapid removal of surface runoff from the carriageway. The most
commonly used methods are through direct and positive discharges to the nearest watercourse
(with routing through a gully pot system) or by indirect drainage involving a soakaway system
prior to integrated collection. It is now widely recognised that runoff from highways,
particularly urban roads and heavily trafficked rural roads, contains a range of pollutants which
can have detrimental impacts on receiving waters, both ground and surface. Sections 4.2 to 4.4
of this Chapter identify the major types of pollutants and the practices and procedures that lead
to their build-up on highway surfaces and subsequent wash–off during rainfall events.
The legal considerations with respect to the potential polluting capabilities of highway runoff
on surface waters and groundwaters are discussed in Section 4.5. The relevant European
legislation, as well as that specific to the UK, is outlined and appropriate case studies are used
to illustrate existing legal cases. The roles and responsibilities of the different authorities with
regard to the pollution control from highways are discussed and the problems in dealing with
accidental spillages are highlighted.
The objectives of Sections 4.6 and 4.7 are to provide guidance on the best practice concerning
the treatment of highway runoff. Particular emphasis is placed on the potential of treatment
systems to achieve the required pollutant performance whilst maintaining cost effectiveness
both in terms of capital and operating costs. The use of sustainable systems which are able to
treat highway runoff to the same efficiency as conventional methods (such as those based on
settlement) is considered important. Ideally the chosen treatment system should enhance the
ecological and aesthetic qualities of the local environment. The selected treatment option will
be highly dependent on the area of land available and on the surface topography. It is also
important to balance the treatment requirements against the need for flow attenuation of the
highway discharge to prevent downstream flooding. In many cases, it is possible to make these
two requirements mutually compatible by using a storage facility which maximises treatment
potential. This Chapter concludes by identifying important recommendations for minimising the
impact of highway runoff on the environment.

4.2 Pollutant accumulation on highway surfaces
The major sources of pollutants to highway surfaces are identified in Figure 4.1 together with
the important processes by which they are introduced and removed from the environment. The
reference parameter for the estimation of accumulation rates on highway surfaces is the
build–up of particulate material, also referred to as “dust and dirt (DD)”, and which represents
those particles with a mean diameter of less than six millimetres. Ellis and Revitt (1989) have
reviewed the most commonly applied accumulation models for solids on road surfaces. A
summary of highway accumulation loadings (kg or g/ha/year) from data provided by European
studies is given in Table 4.1. The data relate to surveys carried out in the 1970s and 1980s and
therefore, for certain pollutants such as lead, may not represent the current situation. In
addition, the average daily traffic densities (ADT’s) refer to different types of highway including
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

67

Vehicle derived exhaust
emissions
Fuel and lubricant losses
Tyre and car fabric wear
Spillages
Industry
Natural sources

Direct input
Deicing compounds

Domestic sources
including litter,
paint and plastics

Dustfall and
Rainfall
Vegetation debris

Atmospheric
movement via
wind

Atmospheric
losses through
splash and spray

Transport to road
gully pots and
storm sewer pipe

Surface washoff

STREET SURFACE SEDIMENTS

Discharge to
surface and/or
groundwaters

Road surface
erosion

Removal by
road cleaning

Figure 4.1: Major sources and pathways of pollutants in the highway environment.
68

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Vehicles
/day
(ADT)
<5000

kg/ha/year
Total
solids

5000–
15000

2218–
3640
479–
7289

15000–
50000

848–
873

>50000

1930–
10410

g/ha/year

COD

Pb

Zn

Cu

Cd

Oil

0.30

0.40

0.39

207

0.360.68

0.7–
0.89

0.13–
0.87

0.007

4.9

557–
672

1.1–
1.3

2.3–
2.9

0.5–
0.6

0.03

1.68–
3.0

2.06–
5.8

3.19

27–43

Table 4.1: Traffic related pollutant loadings (based on European data).
residential roads (<5000 vehicles/day), urban roads (5000–15000 vehicles/day), rural
motorways (15000–50000 vehicles/day) and all types of motorway (>50000 vehicles/day).
A recent analysis of highway runoff data from Texas, US has suggested that total suspended
solids loads were dependent on the characteristics of the current storm, antecedent dry period,
and the preceding storm indicating the importance of build–up and wash–off processes. The
same study showed that oil and grease were dependent only on conditions during the current
storm, such as runoff volume and number of vehicles during the event (Irish et al , 1998). The
possible existence of pollutant specific explanatory variables has important implications for
treatment selection. European data has demonstrated a good relationship during storm
conditions between traffic weighted discharge loads and the rainfall runoff ratio (Stotz, 1987)
implying that the reduction of ratios by discharging runoff over permeable vegetated surfaces
(see Section 4.6.1) would lead to a lowering of pollutant loadings.
Table 4.1 indicates that it is at traffic densities greater than 15,000 AADT (Annual Average Daily
Traffic) that the major detrimental impacts of highway runoff are most likely to occur within
receiving water bodies. However, actual impacts will depend on specific local circumstances at
the discharge point and on the dilution ratio available in the receiving water as dilution and
mixing rates are key controlling factors.

4.3 Classification of highway pollutants
At least 75% (by dry weight) of the total pollutant load washed from the highway surface is
derived directly from vehicles or indirectly through road surface degradation, with the
remainder coming from atmospheric sources and/or from maintenance operations (Ellis and
Revitt, 1991). Spray and turbulence from passing traffic remove as much contamination from the
highway surface as is flushed by runoff during rainfall events. However, spray and deflationary
pollutants are confined to within 10m–15m of the road edge and rapidly become fixed by the
vergeside vegetation and soil.
Table 4.2 provides a listing of pollutant flow–weighted Event Mean Concentrations (EMC) and
loadings associated with highway discharges in the UK. The quoted EMC ranges indicate the
possible variability in the quality of highway runoff. The standard deviations are approximately
75% of each quoted EMC, hence an “average” urban highway carrying more than 30,000
vehicles per day could be expected to produce runoff with a total suspended solids (TSS) EMC
of 261mg/l with a standard deviation of 195mg/l.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

69

Contaminant

Total
suspended
solids

Event mean concentration (EMC)
and concentration range (mg/l)
Rural and
Motorway and
suburban roads
trunk roads

Loads per Unit
Area
(kg/imp.ha/year)
runoff)

Loads per Unit
Runoff
(kg/ha/mm

1.1–11.8

(41)
11–105

(261)
110–5700

815–6289

(17)
8–25

(24)
12.2–32.0

90–172

770–11610

1.3–27

(386)
159–2174

Total Zn

(0.08)
0.02–1.9

(0.41)
0.17–3.55

1.9–19.0

0.003–0.04

Total Pb

(0.07)
0.01–0.15

(0.96)
(34–2.41)

1.1–13.

00.006–0.024

(0.04)
0.01–0.12)

(0.15)
0.05–0.69

0.4–3.7

0.015–0.163

0.01–43.3

0.001–0.17

2.8–31.0

(28)
7.5–400

BOD5

Chloride

Total Cu

Oil/Total
hydrocarbons

Table 4.2: Pollutant concentrations and loadings in UK highway discharge.

4.3.1 Solids
Solids collect on road surfaces and are held within the pores of the road surface structure but, in
particular, they collect adjacent to the kerb–side. Their impact is both in terms of their physical
nature, particularly particle size and also in relation to the variety of chemical pollutants,
including metals and organic pollutants, which can be attached, with different affinities to the
surface of the particulate material. The particle size influences the efficiency of removal of road
sediments during cleaning processes (see Section 4.4.6) and the ease with which the particles are
removed in runoff as suspended solids during rainfall events. Typically wide gradations of solids
ranging in size from finer than 1µm to larger than 10,000µm are found in the runoff from paved
surfaces (Sansalone et al , 1998). The same study found that particles in the size range, 425µm to
850µm, presented the greatest total surface area for pollutant adsorption with associated
implications for pollutant treatment strategies. Highway derived solids which are washed into
receiving waters can exert detrimental ecological effects due to substrate smothering, reduction
of light penetration due to increased turbidity, and a lowering of the oxygenation potential. In
addition, any weakly adsorbed toxic pollutants may be released into the aqueous phase and
become more directly available for uptake by the existing flora and fauna.
70

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

4.3.2 Metals
The metals that have been most widely studied due to their occurrence in road dusts are
aluminium (Al), cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), lead (Pb), manganese
(Mn), nickel (Ni), and zinc (Zn). More recently interest has been raised with regard to those
metals which are used as catalysts in catalytic converters that is platinum (Pt), palladium (Pd)
and rhodium (Rh). The most commonly reported metals in street dusts are Cd, Cu, Pb and Zn for
which the following ranges of concentrations have been reported for all types of highway during
the past 25 years: non–detectable – 11.4µg/g, 25µg/g –1700mg/g, 35mg/g–10700µg/g and
96µg/g–3173µg/g, respectively.
The impact of metals in environmental samples is not only influenced by their overall
concentration but also by their distribution between different physico–chemical forms. Metal
speciation results are particularly relevant for determining the origin, mode of occurrence,
physico–chemical availability, mobilisation and transport of metals in the highway
environment. In addition, important information regarding the bioavailability and possible
potential toxicity of particulate associated metals, in a receiving water following wash–off, can
be deduced. The relevant water quality standards with which aqueous metal concentrations
should be compared are discussed in Section 4.5.2.
Significant concentrations of metals especially Zn, Cu and Fe are mobilised during the initial
“first–flush” period of a storm event and elevated metal levels can occur also with snow
accumulation alongside highways (see Section 4.4.5). The dissolved metal fraction, which is
influenced by the acidity, total organic carbon content and hardness (expressed in terms of
CaCO 3 ) of highway runoff, exerts the greatest ecotoxicological impact on receiving waters.
However, a recent study relating to East Anglian rivers has found that the Zn, Pb and Cd
concentrations in sediments and selected invertebrates did not differ significantly between sites
upstream and downstream of road runoff discharges which was consistent with minimal
differences in ecological diversity (Perdikaki and Mason, 1999).

4.3.3 Hydrocarbons
The hydrocarbons found in the highway environment are normally those associated with the
petrochemical products used in road construction (for example, bitumen) and those more
volatile products used as fuels and engine additives. Because of their non–polar characteristics
the different hydrocarbons become firmly attached to road sediments and remain in this
condition when transferred to the aqueous environment with typically 70%–75% of the total
hydrocarbon load in highway discharges being associated with suspended solids. Methyl
tertiary butyl ether (MTBE), which is used as an additive in unleaded fuels, is of significant
concern because of its elevated solubility in water compared to other vehicle derived organic
compounds. Environmental levels of MTBE arise mainly from spillages and concentrations in the
range of 0.1µg/l–0.2µg/l have been recorded in groundwaters underlying motorways in SE
England. Total hydrocarbon (oil) levels in road runoff are shown in Table 4.2 with elevated
levels (up to 400mg/l) having been recorded during short, intense storm events when suspended
solids levels are high (Colwill, 1984).
Hydrocarbons can cause problems in receiving waters due to the build up of a surface film,
which can reduce the efficiency of oxygen transfer to the water body. There is a tendency for
hydrocarbons to accumulate in bed sediments and to be either gradually released by natural
leaching processes or to be released in high concentrations during times of sediment
disturbance. Both aliphatic and aromatic fractions are List I substances under the terms of the
Groundwater Directive (see Section 4.5.4), and can be highly toxic leading to suppression and
mortality of key invertebrate organisms (such as the freshwater shrimp Gammarus pulex ) at the
bottom of the food chain (Boxall and Maltby, 1995). Through the use of a range of toxicity
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

71

measurements, Marsalek and Rochfort (1999) have demonstrated that acute toxicity can be
frequently detected in highway runoff with the main toxicants being PAHs, metals and
chlorides.

4.3.4 Inorganic salts, herbicides and bacteria
Inorganic salts, such as nitrates and phosphates, may find their way on to highway surfaces due
to the use of fertilisers in the adjacent environment. Other salts, including chloride and to a
lesser extent bromide and hexacyanoferrate (II) are introduced to the highway environment as a
result of winter de–icing activities (see Section 4.4.6). Although the concentrations of
hexacyanoferrate (II) are likely to be low in road runoff, recent evidence has shown their
potential for breakdown by photodecomposition into free toxic cyanide ions (Novotny et al ,
1998). Concerns have been raised about the high levels of chlorides in surface and ground
waters in the US (Lord, 1989), and as a consequence most States require salt applications to be
used wisely so as not to create excessive waste. An alternative to sodium chloride is calcium
magnesium acetate which is less corrosive than chloride salts, less toxic to aquatic life, and has
been shown to have lower abilities with regard to the mobilisation of trace metals from roadside
soils (Amrhein et al , 1993). It should be noted, however, that there is a significant cost
differential between the two chemicals.
The triazine group of herbicides (particularly atrazine and triazine) have been widely used in
the past as weed control agents on highway verges, embankments and central reservations.
Following the banning of the non–agricultural use of triazines in May 1992, many users have
changed to alternative herbicides, such as glyphosate and diuron. The latter is a persistent
herbicide and following application to roadside verges in a residential area, peak levels of
248µg/l with an event mean concentration of 134µg/l have been measured in the runoff
produced by a spring rainfall event (Ellis et al , 1997). This herbicide should only be used after
an assessment of the receiving water environment has been carried out.
The specific sources of bacterial contamination on highways are unclear but contamination
tends to be worst in highly populated residential areas with significant levels of indicator and
pathogenic microorganisms having been recorded in the runoff from these areas (Jacobs and
Ellis, 1991). This problem is mainly confined to urban areas where geometric mean levels in
road surface dust and dirt of 112N/gram–83,000N/gram for faecal coliforms (FCs) and up to
1800N/gram for faecal streptococci (FS) have been reported (Ellis, 1993).

4.4 Sources of highway pollutants
4.4.1 Vehicle emissions, vehicle part wear and vehicle leakages
Vehicle exhaust emissions include volatile solids and hydrocarbons (aliphatic hydrocarbons and
polycyclic aromatic hydrocarbons – PAHs), which are both derived from unburned fuels and, in
the case of PAHs, are produced as a result of chemical reactions within the engine and exhaust
system. The major toxic component of vehicle exhausts has historically been due to the
presence of Pb compounds as a consequence of the addition of tetra–alkyl Pb compounds to
petrol as anti–knock agents. The complete phasing out of leaded petrol in the UK from 1 January
2000 will significantly reduce the Pb problem but will lead to increasing concerns about the
influence of additives such as MTBE within the highway environment, particularly with regard
to air quality effects (see Chapter 5).
Vehicle part wear occurs as a result of abrasion and corrosion processes involving tyres, brake
and clutch linings, and moving engine parts. The main pollutants arising from these processes
are metals although polymeric hydrocarbon (rubber) particles result from tyre wear in sizes
72

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

increasing from 0.01µm. A variety of metal compounds are used as fillers in tyres including Pb
oxides as well as Zn and Cd compounds. Copper is present in brake linings at high
concentrations (for example, 30,600µg/g) to provide added mechanical strength and to assist
heat dissipation. Other vehicle parts which produce metals due to erosion/abrasion processes
include metal plating and bodywork (Cu, Cr, Fe and Ni), moving engine parts (Cu, Cr, Fe and
Mn), and bearings/bushes (Pb, Cu and Ni).
Leaks from lubrication and hydraulic systems during normal vehicle operation can provide a
consistent source of hydrocarbons to highway surfaces. Running losses of total hydrocarbons
have been reported to be in the range of 0.2g–2.8g per mile driven (Wixtrom and Brown, 1992).
Used engine oil also contains metals such as Ba, Ca, Mg, Zn, Cu, Fe, Cd and Pb (ZiebaPalus,
1998) with zinc dithiophosphates being added to motor oil as stabilising additives.

4.4.2 Road surface erosion
The wear of road surfaces can lead to the release of both fine and coarse sediments, as well as
aromatic hydrocarbons and certain metals (particularly Ni) which are associated with
construction materials. Sartor and Boyd (1972) identified three factors which affect the
generation of materials from road surfaces: the age and condition of the surface; local climatic
conditions; and leakages and spillages of fuels and oils, which hasten the degradation of
asphaltic surfaces. Chromium, along with Cu, Ti and Zn, is known to be used in road markings
but unless the paint is in poor condition only a small contribution to road dusts should be
expected.

4.4.3 Accidental spillages
Accidental spillages (involving either solid or liquid materials) can cover relatively minor
incidents such as the small losses of fuel from vehicles to large–scale losses from transportation
vehicles. The potential problem will be greater if the spillage occurs during wet weather
conditions when there is an increased probability of the spilled material being washed off the
road surface into the adjacent drainage system. The procedures for dealing with accidental
spillages are discussed in Section 4.5.5.

4.4.4 Atmospheric deposition
Atmospheric deposition (by either wet or dry processes) represents an important pathway by
which pollutants reach highway surfaces both from within and from outside the highway
environment. The dry deposition process is strongly dependent on deposition velocity, which
can vary by three orders of magnitude, and consequently the contribution of dry atmospheric
fallout to road dusts can be highly variable. The loads of particulate associated pollutants in wet
deposition are strongly influenced by the length of the antecedent dry period. A recent study in
North Carolina indicated that up to 20% of TSS, 70%–90% of nitrogen loadings and 10%–50%
of other constituents in highway runoff had originated from atmospheric deposition during dry
and wet weather conditions (Wu et al , 1998).

4.4.5 Seasonal maintenance practices
The main influences of seasonal practices on highway pollution relate to the impacts of road
salting practices during winter months to prevent surface icing and the use of herbicides to
reduce the impact of weeds during the summer growing season. Common salt is the most
commonly used de–icing agent with urea and glycols being possible alternatives. Abrasives
(grit) are sometimes used to give additional traction on steep slopes. However, grit can cause
drain blockage as well as release airborne particulates and need to be cleared at the end of the
winter. Urea is sometimes used for bridge deck de–icing but is readily flushed into receiving
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

73

waters with the onset of snowmelt. Subsequent hydrolysis to un–ionised ammonia, even at very
low concentrations, can create a toxic environment for fish (see Section 4.5.2). Glycols are
extensively used within airports to prevent the icing of both runways and aircraft (Ellis et al ,
1997) but their cost inhibits widespread use in the highway environment. Accumulated snow at
the sides of busy roads has been shown to be an efficient collector of inorganic pollutants
derived from vehicular sources (Viskari et al , 1997). Within the snow deposits, pollutants have
been shown to be mainly particulate associated but more than 50% was transferred to the
soluble phase within the melt waters (Viklander, 1996). The practice of snow piling at the sides
of roads for extensive winter periods should therefore be avoided.
Rock salt, which is used for de–icing purposes on roads, is subject to a British Standard (BS
3247:1991). The currently recommended application rates for de–icing salt are 10g/m 2 as a
precaution against ice (increased to 15g/m 2 if the salt is wet due to open storage) and
25g/m2–40g/m 2 if freezing conditions are expected after rain or snow (DoT, 1992). The
advantages of using salt have to be balanced against its corrosive impact on vehicles and street
furniture that can lead to enhanced deposition of metals on to highway surfaces. Rendahl and
Hedlund (1998) have shown that cosmetic corrosion decreased by 50% on cars used on
unsalted roads compared to those driven on salted roads. Salt is known to have harmful physical
and chemical effects on vergeside vegetation and aquatic ecology although both effects are
normally short–lived and associated with winter salting events.
In spite of winter salt concentrations discharged from the highway surface reaching high levels
(see Table 4.2) there have been no reports of increased chloride concentrations in British
groundwaters (Luker and Montague, 1994). Although concentrations above 400mg/l in receiving
waters can stress sensitive fish and invertebrate species, the existence of high dilution ratios
minimises such impacts and it is rare for chloride levels greater than 200mg/l, the maximum
acceptable value for drinking water, to occur.
The control of weeds in the highway environment during the growing season is necessary to
prevent structural engineering damage, to maintain safety aspects and provide an appropriate
aesthetic impact. A typical annual load of herbicides applied by local authorities in the UK is
186 tonnes of which 94% are used in the weed control programmes of roads and highways,
parks, amenity grass and municipal paved areas. The key factors that affect the movement of
herbicides applied to hard surfaces, in storm runoff are persistence, adsorption, rainfall
intensity, and the time period between application and rainfall. Although herbicide degradation
will commence immediately, the ideal application programme will involve frequent
applications of low doses, and preferably during dry weather conditions. The excessive use of
pesticides (in all environments) has led to concerns about their increasing presence in surface
waters, groundwaters, and drinking water resources. The EC Drinking Water Directive
(80/778/EEC) became UK law in 1989 with its incorporation into the Water Supply (Water
Quality) Regulations and specifies a maximum admissible limit of 0.1µg/l for individual
pesticides and 0.5µg/l for total pesticides. Research in an urban catchment in Essex has
consistently shown diuron concentrations in excess of these levels in surface waters receiving
runoff from highway and other urban hard surfaces (Revitt et al , 1999).

4.4.6 Regular maintenance practices
Regular maintenance practices include mechanical road sweeping, the flushing of pollutants
from the road surface (induced either by artificial means or by natural rainfall events), and the
cleaning of gully pots. Conventional street cleaning practices are most effective in removing
large particle sizes and Sartor and Boyd (1972) have observed the 70% removal of sediment
particles larger than 2000 µm compared to only 15% of those finer than 43µm. It is with these
fine particles that the majority of the pollutants are associated and therefore for which efficient
cleaning practices are required. The efficiency of road sweeping is improved with greater
74

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

numbers of “runs” over the surface area and pollutant removal is also dependent on the method
employed. Vacuum sweeping has been shown to be most effective followed by manual
techniques and with mechanical sweeping being the least effective (Ellis, 1979). Hydrojetting is
also used although studies in Paris have shown the existence of highly variable efficiencies for
solids (20%–65%) and metals (0%–75%) with no significant removal for PAHs (Bris et al , 1999).
Another problem with this technique is that pollutants are transferred directly from the highway
surface to the gully pot and the below–ground drainage system.
There are over 17 million roadside gully pots in service within England and Wales, each 450mm
standard diameter pot having a nominal capacity of 80 litres for a typical catchment area of
200m 2 –280m 2 per gully. Design criteria for gully pots are given under British Standards 6367
(BSI, 1983). The total solids trapping efficiency of road gully pots ranges between 15%–95%
depending on inflow, pot size and maintenance condition but for a typical particle size
distribution, the overall total solids reduction (for sizes greater than 300µm) might be expected
to be 70%–75% (Butler and Karunaratne, 1995). Trapped gullies are more efficient at separating
oil but require more regular maintenance than untrapped gullies. An untrapped gully can retain
much more silt by virtue of the greater sump depths and can store up to 20% of the mean annual
volume discharged by runoff events from the highway surface.
During dry weather periods and especially during summer, rapid drops in dissolved oxygen can
lead to the establishment of anaerobic conditions and the release of soluble organics,
ammoniacal compounds, dissolved metals as well as sulphides into the supernatant liquor of the
gully pot. The next storm event rapidly displaces this standing liquor into the stormwater sewer
pipe with intense flow events (exceeding 3l/s–4l/s) causing hydraulic disturbance in the sump
chamber which can overturn the settled sludge and also discharge this septic material into the
surface water sewer. In this way, the gully pot can comprise a major source of highway pollution
and be a significant contributor to the “first–flush” shock load experienced by the receiving
water. Butler and Memon (1999) have modelled the typical wet weather processes which occur
within gully pots (including dilution, dispersion, sedimentation, washout of suspended and
dissolved pollutants, and reaeration). Recommended procedures for the management and
cleaning of gully pots to achieve control of pollutant outflows from the chamber into the storm
water drainage system can be obtained from a previous report (CIRIA, 1998). Required cleaning
frequencies will be location specific and therefore careful monitoring is needed to identify
critical pollutant and sediment accumulations. Individual highway maintenance authorities will
need to assess the cost–benefit of implementing a regular cleaning protocol.

4.5 Legislation and responsibilities
4.5.1 Legislation and legal liability
In England and Wales, the Environment Agency (EA) has statutory duties and powers under the
1991 Water Resources Act (WRA) for flood defence, pollution control, water resources,
fisheries, recreation, conservation and navigation. Similar duties and powers rest with the
Scottish Environmental Protection Agency (SEPA) and the Department of the Environment in
Northern Ireland. The right to discharge road runoff to surface waters through highway drains
“A highway authority or other person entitled to keep open a drain by virtue of section 100
of the Highways Act 1980 shall not be guilty of an offence under Section 95 by reason of his
causing or permitting any discharge to be made from a drain kept open by virtue of that
section unless the discharge is made in contravention of a prohibition imposed under
Section 86”.

Box 4.1: Section 89(5) 1991 Water Resources Act.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

75

(which include ditches, gutters, soakaways, culverts and pipes) is established in the 1980
Highways Act ( s.100 ) and under s.89(5) of the 1991 Act the highways authority does not require
the statutory defence of a discharge consent (see Box 4.1). However, under a liaison agreement,
the measures required to prevent or alleviate pollution will be agreed through consultation
between the EA and the highways authority or its agent prior to construction under the various
provisions contained in the 1990 Town & Country Planning Act and the 1991 Town & Country
Planning (Development Plan) Regulations. Similarly in Scotland, road drains serving trunk roads
and motorways are owned by the Scottish Office and as such, are subject to Crown exemption
from control by the regulator.
The planning legislation allows the EA to make representation opposing development projects
(including new or improved highways), which are likely to have an unacceptable impact upon
the aquatic environment and a series of Planning Policy Guidance (PPG) notes on pollution
prevention and surface runoff control have been published by the former National Rivers
Authority (see Box 4.2) including a policy implementation guidance note (SC/CC/014;
September 1992) for highway discharge. Additionally, local authority Unitary Development
Plans (UDPs) are required to take into account the environmental implications of direct
discharges to ground (see Box 4.2) and specific requirements may be imposed by the EA in
relation to groundwater protection (see Section 4.5.4). However, the EA could choose to apply
the provisions of s.86 WRA 1991, to serve a Conditional or an Absolute Prohibition Notice to
an existing or proposed highway drain if it saw fit to do so because of some particular pollution
hazard. This could either require that a consent be obtained (under Schedule 10, para. 5(1),
WRA 1991) or alternatively it may specify the conditions to be observed prior to the making of
the discharge.
The criminal defence against highway discharges embodied in s.89(5) of the 1991 Water
Resources Act does not hold against liability arising under civil case law for flood damage or
pollution resulting from discharge of road runoff (s.100 WRA 1991). This potential for strict civil
liability arises where pollution from highway drains is “caused or knowingly permitted” into
controlled waters. The 1993 Cambridge Water Company case also confirmed that foreseeability
is an essential element in establishing civil liability in respect of pollution of controlled waters.
The court decision on the case means that if it can be established that a surface water runoff
event from highways is known to have a potentially contaminating effect upon surface or
groundwater sources then the potential for strict liability arises.
More persistent watercourse pollution is often associated with highway construction activities
and in the past either little formal action has been taken against such offenders or the fines
imposed have been derisory. Regulatory authority attitudes towards negligent construction
contractors and site agents are now becoming harder as evidenced by legal proceedings
instituted by SEPA against contractors involved in the construction of the M74 in SW Scotland.
Persistent pollution incidents during the summer of 1993 of the Class 1 salmonid waters of the
Rivers Annon and Kirtle Water (with TSS concentrations varying between 103mg/l–46800mg/l
compared to an imposed standard of 60mg/l), resulted in successful prosecution under s.31 (1)
of the 1974 Control of Pollution Act.

4.5.2 Water quality objectives and standards
Under the provisions of the 1991 Water Resources Act, the National Water Council (NWC)
classification scheme of absolute measures of receiving water quality has been replaced with a
General Quality Assessment (GQA) to be applied to a given river reach and a Rivers Ecosystem
(RE) classification for the statutory Water Quality Objectives (WQOs) required to meet specified
local use–related needs. The former addresses four main categories (or Windows) covering
General Chemical, Nutrients, Biological and Aesthetic Quality, whilst the RE classification
establishes clear quality targets (and specified compliance dates) for all controlled waters on a
statutory basis. Details of the existing Chemical Window and the recently issued draft form of
76

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Figure 4.2: Water Quality Assessment Schemes.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

77

Fair

D Worse than expected; sensitive
taxa scarce; some pollution
tolerant species in large numbers

4. AESTHETIC
QUALITY

F Limited to few pollution tolerant
taxa; or no life present

E Restricted to pollution tolerant
species; a few taxa dominant;
sensitive taxa rare or absent
Bad

Poor

C

Fairly
Good

C Worse than expected; many
sensitive species absent; rise in
pollution tolerant taxa

F

E

D

B

B Short of expected; small
reduction in pollution tolerant
taxa

A Better than expected; high
diversity; several species in each
taxa
Good

GRADE

A

Water
Quality

Very
Good

3. BIOLOGICAL QUALITY

2. NUTRIENTS

GENERAL QUALITY
ASSESSMENTS (GQA)
(For survey assessment
purposes)
Will consist of FOUR separate
WINDOWS as given below

-–

20

50

60

70

80

DO
% Sat
10%ile

-

15

8

6

4

–

9.0

2.5

1.3

0.60

–

–

300
2000

300
2000

30
300

1. CHEMICAL
BOD
Total
Total
mg/l Ammonia Zinc
90%ile
mg/l
µg/l
90%ile 95%ile
2.5
0.25
30
500

–

–

5
112

5
112

5
112

Dissolved
Copper
µg/l
95%ile
5
112

WATER QUALITY ASSESSMENT
SCHEMES
(Formerly consolidated within
the NWC scheme)

–

–

≤10
>100

≤10
>100

≤10
>100

≤10
>100

Hardness
mg/l
CaCo3

RE5

RE4

RE3

RE2

RE1

RIVER
ECO–SYSTEM
(RE) WQOs

4

3

2

1b

1a

Former
NWC
System

WATER QUALITY
OBJECTIVES (WQOs)
(On pass/fail basis for
management purposes)

“Particular attention should be paid to the protection of groundwater resources which are
susceptible to a wide range of threats arising from land use policies. Changes in land use
may affect the availability of groundwater resources by restricting recharge or diverting
flows”.
Para.3.6 Guidance Notes for Local Planning Authorities (LPA) on the Methods of Protecting
the Water Environment through Development Plans. 1994 National Rivers Authority (NRA).
“The LPA, in consultation with the NRA, will assess the surface water runoff implications of
new development proposals. New developments will only be permitted where the LPA is
satisfied that suitable measures, designed to mitigate the adverse impact of surface water
runoff, are included as an integral part of the development”.

Box 4.2: Para. 6.19 Planning Policy Guidance Note 12. Development Plans and Regional
Planning Guidance. 1992 Dept of the Environment.
the Biological Window are shown in Figure 4.2 which also illustrates the structure of and
relationships between the new water quality assessment approaches and the previous NWC
system. In the event that both a WQO and a GQA exists for a particular water, then the EA will
be legally obliged within a specified period, to improve the water quality such that the GQA is
similar or better than the WQO equivalent parameters. As such therefore, the statutory WQO of
the receiving water will dictate the treatment level required for highway runoff. Where statutory
WQOs do not exist, either the GQA or interim, non–statutory WQOs will be used. Where a
stream reach supports more than one use–function, and where both statutory and non–statutory
water quality requirements pertain, the most stringent of the combined specifications will apply.
Therefore the assessment of new roads or road improvements must include consideration of all
the uses (both upstream and downstream) to which the watercourse is put.

4.5.3 EU legislation
The Framework Dangerous Substances Directive (76/464/EEC) and its daughter directives
identify toxic List I and II substances that are defined not exclusively in terms of their presence
but more by their effects. Highway runoff pollutants under List I would include hydrocarbons in
addition to asbestos from brake linings as well as Cd and Pt from vehicular sources such as
batteries, tyres and exhaust systems. List I substances also include herbicides and pesticides
which are applied to highway verges for weed and pest control (see Section 4.4.5). The Quality
of Freshwaters Directive (78/659/EEC) in respect of the protection of fish life includes water
quality standards for suspended solids, Cu, Zn, Cd, Pb, herbicides, hydrocarbons and PAHs; all
of which are frequently present in highway runoff.
Annex II of the Environmental Assessment Directive (85/337/EEC) and its subsequent
amendment (97/11/EC) requires that a full environmental assessment is undertaken prior to
development consent being given for those projects (including highways) which are deemed
likely to have a “significant effect” upon the environment. The statutory instrument which
transposes Directive 85/337/EEC and amendment 97/11 into highways legislation is the
Highways (Assessment of Environmental Effects Regulations) 1999.
Under the 1992 Local Government Act, the powers of local authorities may be delegated to
individual officers who can make decisions on whether assessments are needed for road
projects of local significance. A very recent High Court case (see Box 4.3) however, resulted in
the quashing of a local authority’s decision to approve a minor road scheme for which no formal
environmental assessment was carried out and may well cause authorities to be more careful in
dismissing the need for environmental assessment where only “local” impacts are involved. One
78

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

A planning application submitted by a Bury St Edmonds company for an access road to its
brewery depot was reviewed by a planning officer who judged that no assessment was
required and permission for the road was then granted by the council’s planning committee.
The access road was intended to relieve the town centre of further heavy goods congestion
but the route would cross water meadows of historical and local amenity value.
The original application was not accompanied by any formal environmental statement but
did include commissioned expert reports on landscape, traffic and ecological impacts. A
local resident challenged the validity of both decisions by way of judicial review and the
court held that both decisions were legally defective and argued that, “a road may have a
significant effect albeit that its effect is local”.

Box 4.3: R v. St Edmondsbury Borough Council ex parte Walton. 1999.
of the key changes brought about by amendment 97/11/EC is that the planning authority (or
Secretary of State) must now adopt and publicise a formal decision as to whether a project
falling under Annex II (that is those classes of projects which fall outside Annex I and do not
require a compulsory environmental assessment but which by virtue of their size, location or
nature may have an environmental impact), potentially has “significant effects” on the
environment.

4.5.4 Groundwater regulations
Groundwaters constitute a substantial proportion of freshwater resources in the UK and are very
difficult to rehabilitate once they become polluted (see Box 4.2). WQOs have not yet been
established for groundwater but the 1998 EA “Policy and Practice for the Protection of
Groundwater” (PPPG) document lays down a guidance framework that is confirmed within the
1998 Groundwater Regulations. The policy has also been adopted by SEPA. The framework is
set out as a series of policy statements based on the principles of potential hazard, risk,
exposure and vulnerability and is supported by a series of regional groundwater vulnerability
maps. The PPPG also defines drainage from “major roads” as constituting any positive drainage
system concentrating runoff from a paved surface. Three annular groundwater Source Protection
Zones (SPZs) have been prescribed under the policy which aims to give broad indications of
potential groundwater risks from particular types of development. Figure 4.3 defines the SPZs
and associated aquifer Resource Protection groups together with the likely EA responses (as
given in the Acceptability Matrix 3c of the PPPG), to proposals for highway discharges to ground
via soakaways or other infiltration devices.
Also relevant to the disposal of highway runoff are the NRA Policy Statements covering diffuse
pollution to groundwater (Policies G1–G4) particularly with reference to the leaching of
herbicides and other maintenance chemicals from highway verges and landscaped areas.
Specific guidelines for the use of chemical sprays are covered in the 1996 Highways Agency
trunk road Maintenance Manual (Volume 2), Routine and Winter Maintenance Code . This code
of practice advocates the use of specified herbicides only in exceptional circumstances or
where there is a particular need such as around motorway/trunk road marker posts and signs or
along kerb lines.

4.5.5 Spillages and emergencies
Some 80 million tonnes of “dangerous” goods are carried annually by road transport in the UK.
The range of substances carried is extremely wide and the Department of Transport Circular
7/87 Spillages of Hazardous Substances on the Highway provides recommendations regarding
the accidental spillage of these substances on the highway. An appendix also provides a
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

79

Figure 4.3: Highway Discharge Acceptability Matrix.

80

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Discharge to conventional shallow soakaway or
filter drain but could also adopt Option 2 methods

3

Note: Oil interceptors may be required
at any site and this will need to be
determined with the regulatory authority.

Discharge to swales/retention ponds/detention
basins/wetlands with either overflow to
infiltration or soakaway

Non Aquifer

OI*

RE3/RE4
L S M

L

RE5
S M

Infiltration and/or detention/retention
methods (sedimentation lagoons/tanks,
balancing ponds, wetlands)

4

L, S and M; Low, Significant and Major Potential Impact (see text for
detail)

As Option 2 plus other infiltration methods
(trench/basin)

Discharge via porous paving/soakaway/filter
strip/swale acceptable

No treatment required

RE1/RE2
L
S M

Discharge to Surface Water

3

2

1

Options to
Surface Water

Deep
Watertable

Other Areas
of Aquifer
Shallow
Watertable

2

Deep
Watertable

No discharge to ground by soakaway or seepage.
Surface water disposal by some other means

Shallow
Watertable

Inside Groundwater
Protection Zone
Inner Zone
Outer Zone

Discharge to Ground

1

Options
to Ground

Small Car Parks
Large Car Parks
HGV Parking
Garage Forecourts
Major Roads
(>30,000 AADT)
Other Roads

Discharge
of Highway
Runoff

summary of the law relating to the carriage of dangerous goods which covers load shedding as
well as spillage. The total number of reported pollution incidents in inland waters has risen
continuously over the last ten years with “substantiated” incidents reaching some 33,000 in
1995 within England and Wales (with a further 3580 in Scotland). However, the number of
incidents which can be directly related to transport sources and which are also of “major”
(Category 1) or “serious” (Category 2) concern are small numbering between 50 to 100 per
annum with the larger majority being minor petrol spillages of Category 3 status. Analysis
suggests that on motorways and trunk roads, about three serious spillages occur for every 1000
HGV personal injury accidents, compared with two for every 1000 HGV on non–trunk roads.
Notification procedures for pollution incidents on highways are included in the Health & Safety
Executive RIDDOR Regulations and the Fire Service has a statutory duty under s. 87 of the 1991
Water Resources Act to mitigate the effects of pollution caused by its own emergency actions
such as water flooding to avoid fire or explosion risks. Such pollution control measures
normally involve a “shut–down” or sealing of drain entries. A Memorandum of Understanding
has been agreed between the Environment Agency, the National Assembly for Wales, the
Highways Agency and the Local Government Association on behalf of the Fire Service (see also
the Department of Transport Circular 7/87, Spillages of Hazardous Substances on the Highway ).
Where the installation of pollution control valves (for the emergency storage of spillages), at the
outlet of highway drainage systems is not feasible, specific provision can be made through the
installation of “pollution traps” of approximately 20m 3 capacity to be incorporated on outfalls
to surface waters. There should be suitable isolation valves fitted at both inlet and outlet to
provide the necessary storage. This will enable oily materials to be retained and will also trap
water soluble chemicals in the event of a major spillage. Installation of such facilities should be
considered at roundabouts and interchange junctions and on sections of highway where the
receiving water is judged to be particularly sensitive. When considering the installation of such
pollution traps, an assessment of the risks and consequences of spillages (such as location,
accident potential and emergency response times) should be carried out to evaluate the need for
such facilities. Appropriate advice and methods are contained in of the Design Manual for
Roads and Bridges – Volume 11 (DETR, 1998). Signs indicating the location of any pollution
control valves and related devices should be installed at the roadside and the valves should be
regularly maintained as part of the routine highway maintenance programme.

4.5.6 Highway authorities
The responsible highway authority for motorways and trunk roads in the UK was the former
Department of Transport (DoT) but this has passed to the Secretary of State for the Environment
Transport and the Regions who delegates responsibility to the Highways Agency. The
operational management of trunk roads is distributed on a regional basis to appointed managing
agents. For most other roads, the county council (or London Borough) is the designated
authority although delegation often occurs to a district council to administer local residential
roads. The specific powers vested in a county council in respect of highways are indicated in
Box 4.4 and the council will also be consulted for views on planning applications for
❍ s.38 : power to adopt a highway drain constructed by others
❍ s.100 : power to prevent water flowing into a highway and power to drain water from a
highway
❍ s.101 : power to pipe or fill in roadside ditches, subject to drainage authority consent
❍ s.110 : power to divert a watercourse after consulting the district council
❍ s.339 : power to require developers to seek consent for any works or the use of a
watercourse for highway drainage.

Box 4.4: County Council Highway Powers. 1980 Highways Act.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

81

development when flows to a watercourse from highway drains is substantial. There is provision
under s.21 of the 1936 Public Health Act and the 1991 Water Industry Act, for the dual use of
highway drains or public sewers for the combined drainage of surface waters from roads and
domestic (non–commercial) properties. The joint–use procedure and cost–apportionment is
covered by the 1981 National Water Council (NWC) Guideline Memorandum on Relationships
between Water Authorities and Highway Authorities . The ownership arrangements and
continued use of such highway drains is covered by s.264 of the 1980 Highways Act. Where
road drains are used jointly for highway and property drainage, the sewerage undertaker
normally adopts those lengths in joint use under s.38 of the 1980 Highways Act. However, many
developers favour the construction of highway drains in parallel with public sewers for domestic
surface water drainage with each discharging separately to the same watercourse. In these
circumstances, a highway drain is a private drain owned by the highway authority and may not
be requisitioned.
Whilst there may still be some misunderstandings between, and lack of knowledge about, the
specific powers and roles of the various highway authorities due to the complex enveloping
legal and administrative frameworks, it is quite evident that all the agencies are becoming
increasingly aware of their responsibilities in respect of pollution control from highway
discharges. The concern of the national regulatory bodies is reflected for example in the 1993
NRA guidance notes (SC/CC/014) on Drainage from Motorways, Highways and Other Roads
intended to facilitate integration of specialist engineering, geomorphological and ecological
knowledge into the design and implementation of highway drainage structures. The Thames
Region EA has also recently published (1998) an interim guidance manual on the Treatment of
Highway Runoff Using Constructed Wetlands intended to encourage alternative control and
treatment approaches for highway drainage. The water service companies are also becoming
increasingly committed to such surface water source control approaches which seek to divert
and control rainfall–runoff at source and a preliminary design manual supported by the industry
for urban drainage systems is now available (CIRIA, 2000a, 2000b).

4.6 Treatment of highway runoff
4.6.1 Filter strips and swales
Filter strips and swales are vegetated surface features, which can provide conveyance, storage
and infiltration facilities for highway discharges. Appropriate design allows peak flows and
runoff volumes to be attenuated, with accompanying infiltration processes. These systems are
particularly effective at removing solids and associated pollutants through sedimentation,
biofiltration and chemical adsorption. They can be designed to improve the aesthetic
appearance of the roadside environment and ideally should be located adjacent to the
impervious surface from which they are to receive runoff so that sheet flow either across the
filter strip or along the swale is achieved. These systems are particularly suited for use as source
control treatments for small residential developments, parking areas and roads where they can
be effectively used for “first stage” treatment prior to the use of a further treatment system, such
as an infiltration basin (see Section 4.6.3) or a detention pond (see Section 4.6.4).
4.6.1.1 Grass swales
Roadside and median grass–lined depressions and channels are commonly used as low–cost
practices in North America, Australia, France and Germany to convey impermeable runoff from
the carriageway surface. Knight et al (1998) have described the use of swales as part of a
comprehensive and environmentally sustainable systems for the quantitative and qualitative
treatment of highway runoff in Houston, Texas. However, in the UK, where they have been
constructed principally in association with new industrial/commercial estates, swales only
comprise some 15%–18% of all best management practices (BMP’s) source control devices.
82

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

The minimum residence time should be at least five minutes, which would represent a flow of
0.2m/s travelling through a 60m swale. The overall length should not be less than 20m–25m.
Walsh et al (1997) have confirmed that in addition to the swale length and flow rates, the
vegetation density and type (open channel vs sheet flow) as well as size of contributory area are
significant controlling factors with regard to pollutant removal. Vegetation resistance reduces
flow velocities and increases contact opportunities between the flow and the vegetation and
therefore enhances pollutant removal efficiency. Water quality improvements can be assisted by
the introduction of a level spreader at the inlet and the use of check dams on long swale lengths
or with longitudinal gradients above three percent.
Simple, shallow and broad V–shaped grass troughs (five to eight metres wide with side slopes
up to 9%–12%) have been shown to demonstrate better pollutant removal efficiencies (Walsh et
al , 1997; Murfee et al , 1999) compared to the conventional trapezoidal cross–section swales.
Such forms would also be more convenient for routine maintenance. The range of pollutant
removal efficiencies that can be expected for grass swales receiving highway runoff are shown
in Table 4.3. It is clear that whilst in general, good removal rates can be achieved by such
systems, there is still considerable variability in performance. Very little removal is achieved for
soluble metal species and nutrients. Pollutant loadings in conventional swale channels are
generally below most national criteria for biosolid disposal to land and would suggest
operational site lives of well beyond 50 years especially if given regular and proper
maintenance.
Swales should be regularly inspected (at least twice each year) with particular attention paid to
erosion damage, build–up of silt deposits, excessive waterlogging, and poor vegetation growth.
A minimum grass height of 100mm should be maintained with the frequency of mowing being
dependent on the species of grass and the climatic conditions. Ideally, clippings should be
removed from the site as these can cause blockage of downstream structures or add excessive
nutrients to the storm flows. Excessive silt deposits should be removed to prevent damage to the
vegetation and to maintain the infiltration capability. Easy access to the swale for mowing and
other maintenance equipment needs to be provided.
4.6.1.2 Filter Strips
Filter strips can take any natural vegetated form and although normally consisting of grassed
areas, they can also be in the form of wooded areas. In addition to the characteristics of the
vegetation (ideal height of between 50mm and 100mm) the major factors influencing pollutant
removal efficiency are the longitudinal and cross slopes, and the interaction of the vegetation
with the highway runoff flow. Barrett et al (1998) have recommended the use of filter strips with
side slopes of less than 12% and flow paths of at least eight metres for maximum pollutant
removal effectiveness from highway runoff, which reached 85% for suspended solids. The
actual depth of filter strips may be dependent on the land available but minimum residence
times should be between three and five minutes for the mean annual storm. The use of side kerb
entry slots along the full swale length may be useful to achieve an even flow distribution as may
a gravel–filled trench across the top length of the strip. Yu et al (1987) found that sheet flow over
the grass surface of a filter strip could be achieved using a level spreader and produced average
percentage removal efficiencies of 71%, 38%, 10%, 25%, and 50% for TSS, Ptot, Ntot, Pb and
Zn, respectively in the runoff from a car park.

4.6.2 Filter drains
Filter drains (also known as French drains) are used to collect the runoff from 25% of all roads
in the UK. They consist of perforated drainage pipes normally laid along the edge of highways
in geotextile fabric lined trenches which are back–filled with granular material or lightweight
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

83

Table 4.3: Performance Efficiency and Value of Highway Treatment Systems.

84

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

● Moderate visual
appeal
● Can enhance
habitat value

● Moderate

High

Extended (Dry)
Detention
Basin

Wetland

70–95

50–90

High

Moderate–
High

40–80

High

30–60

30–70

30–50

20–40

20–40

5–20

10–15

10–20

75–95

60–75

40–50

10–35

35–65

45–80

50–85

50–75

30–60

30–50

40–80

60–90

60–75

40– 75

45–85

30–60

20–50

30–60

60–90

70–90

15–40

10–25

5–10

0–5

0–5

20–30

15–25

● Moderate to high
● Costly to replace
plants

● Moderate to high

● High visual and
habitat appeal

● High aesthetic
appeal
● Moderate to high
habitat value
especially
if vegetated

● None

● Moderate to high
● Costly to maintain

Low–
Moderate

Oil/Grit
Interceptor

50–85

30–60

● Moderate to high

● Some aesthetic
value

● Moderate to high
● Costly to desludge

Low–
Moderate

Sedimentation
Lagoon

Retention Basin
● 6–10 hour
retention
● 16–24 hour
retention

● Moderate
visual appeal
● Selective planting
can enhance
habitat value

10–35

20–35

10–20

0

● More costly than
conventional
drainage

10–40

70–90

70–90

10–20

High

70–90

70–90

5–10

Swales

70–80

20–40

–

● Limited habitat
value

20–50

20–30

–

● Susceptible to
clogging

60–90

60–90

10–30

Basin/Trench

Dissolved

● Inconspicuous,
unobtrusive

Total

Metals

● Moderate to high
● Costly to reinstate

Low–High

Infiltration

Hydro–
carbons

● Inconspicuous
● Unobtrusive
● No habitat value

Bacteria

Habitat and
Aesthetic Value

● Low to moderate
● Costly to replace
● Clogging potential

Low–
Moderate

Filter
(French Drain)

Total
Nitrogen

Maintenance
Requirements

● None

High

Gully/Carrier
Pipe System

TSS

% Removal Efficiency

● Low to moderate
● Costly to replace

Hydraulic
Design
Robustness

Treatment
Facility

aggregate. The traditional role of filter drains has been to intercept highway discharges and
transport the flow to a suitable outlet point. However, they also provide a treatment facility
(through adsorption and biodegradation processes) and the expected removal efficiencies of
both conventional and toxic pollutants are shown in Table 4.3.
The identified disadvantages of filter drains (costs of backfill and replacement at approximately
ten year intervals due to aggregate blocking by oil/grease combined with sedimentary material;
maintenance requirements; softening of pavement foundations; groundwater pollution risks for
unlined trenches) have resulted in a policy of non–recommendation of use (Highways Agency
Advice Note 39/38). However, they are being retained in respect of reconstruction works
dealing with large groundwater flows from highway cuttings and on long road lengths with very
flat gradients. Ellis and Revitt (1991) have reported on the practices of enhancing the drainage
capability and the silt–absorbing capacity of filter drains, and hence the lifetime, by using a
backfill with wider and coarser grading than in standard specifications. Such practices would
clearly compromise the potential pollutant removal performance of the treatment system.

4.6.3 Infiltration systems
Infiltration systems for the treatment of highway runoff should be located in areas where the
soils are highly pervious (for example, sandy soils) and as indicated in Section 4.5.4 and Figure
4.3, should not be used where there is any potential for polluting the underlying aquifer (EA,
1998). Improvements in water quality are achieved through physical filtration processes,
adsorption of pollutants by the infiltration media (infill and surrounding soils) and
microbiological removal of pollutants due to reactions on the surface of the media. The natural
infiltration capabilities of green embankments have been commented on by Dierkes and Geiger
(1999) with the highest concentrations of heavy metals and hydrocarbons being found within a
distance of up to two metres from a German highway and in the top five centimetres of the soil.
Similar results have been reported in a study of surface and sub–surface infiltration systems
(Mikkelsen et al , 1997) which showed that these systems served as effective pollutant traps
although they could eventually pose a solid waste disposal problem. The treatment efficiency is
dependent on the contact time between the drainage waters and the infiltration media.
Pre–treatment systems, such as a trapped gully pot, may be needed if high suspended solids
loadings or persistent pollutants are present within the highway discharge.
4 6.3.1 Soakaways
Soakaways provide attenuation of surface runoff by allowing gradual infiltration into the
surrounding soil. There are two major designs based on either the stone filled soakaway or the
chamber soakaway with both types usually incorporating a sump to trap coarse sediment. The
infiltration rate should ensure that the soakaway is half empty within 24 hours of a runoff event
and current design recommendations are for a two hour storm with a return period of ten years
that is, 15mm/hour (BRE, 1991). Nevertheless, soakaway practice may provide minimal
groundwater protection for soluble pollutants, such as herbicides, MTBE and certain metal
species. Tracer tests undertaken on soakaway drainage at the M1/M25 junction in Hertfordshire
indicated that the majority of pollutants were retained in the 0.4m–0.5m soil levels immediately
below the base of the soakaway with an exponential decline with depth to background levels
(Price, 1994).
Where soakaway drainage from major highways is being disposed directly to ground
particularly overlying Groundwater Resource Protection (GRP) zones, interception and/or
treatment facilities are essential. Under such circumstances, drainage from extensive stretches
of highway (perhaps as much as one kilometre) should be brought to lined oil interceptors and
then to a group or “field” of soakaways. Discharges and spillage risks to ground should always
be the subject of a proper assessment and it may be that in the case of rural highways a less
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

85

rigorous containment and treatment approach may be applicable. On the M40 and M25
motorways, follow–on soakage lagoons have been installed to accept drainage overspill if all
the soakaways should fill. The careful design and construction of soakaways is essential to avoid
high maintenance costs and the possible necessity of regular replacement of the infiltration
media which can negate the advantages associated with the relatively low initial costs of these
systems. Soakaways should be inspected annually with specific attention being paid to the
removal of debris from the base of the inspection tube or chamber and the cleaning of any
pre–treatment systems.
4.6.3.2 Infiltration trenches
Infiltration trenches are essentially a linear version of soakaways but require lower volumes of
infiltration material (stone or rubble) for a given water inflow. Narrower systems save on
construction costs but one reason for their lower popularity, compared to soakaways, in the UK,
is the commonly perceived design problem associated with accommodating the required trench
length and width into the land area available. However, the ability to maximise the infiltration
surface area in these systems enables high treatment efficiencies to be achieved (see Table 4.3).
Maintenance practices are the same as have been described for soakaways (see Section 4.6.3.1).
A recently trialled system in the US involves a partial exfiltration trench containing sand
modified with an oxide coating to remove metals through adsorption–filtration mechanisms.
Mass metal removal efficiencies greater than 80% are claimed for a prototype system receiving
highway runoff (Sansalone et al , 1998).
4.6.3.3 Infiltration basins
Infiltration basins are designed to store runoff and to allow it to slowly percolate through the
basin floor, which is either soil or a specially constructed under–drainage system containing
gravel and/or sand filter beds. Infiltration basins can be constructed to the required aesthetic
shape and are generally between 0.5m and 3.0m in depth. It is common practice to incorporate
vegetation cover throughout the basin and to assist with regular mowing (ideal grass lengths
should not exceed 150mm) the basin should have a flat base with side slopes which are not
steeper than 1:4. As for other infiltration systems, one half of the total volume should be available
within 24 hours of a runoff event and the maximum emptying time should be 96 hours.
Infiltration basins are best suited to soils with infiltration rates exceeding 15mm/hour (for
example, sandy loams, sands, sandy gravels). An overall filtration rate of five m 3 /ha/m 2 should
provide for total solids removal efficiencies of up to 90%. Soils should also exhibit a high
sorption capacity and a high resistance to desorption at low pH (Barbosa and Hvitved–Jacobsen,
1999). As for other infiltration systems, maintenance is an important consideration with the
grassed surface needing to be kept clear of silt, organic debris and general litter. Where the
runoff to be treated contains elevated levels of suspended solids it is recommended that a
sedimentation basin, designed to hold the first flush of polluted runoff should be positioned
upstream of the infiltration basin.
The US experience of both on–line and off–line infiltration basins identifies the potential for
effective removal of a range of soluble and fine particulate associated pollutants but raises a
question mark against their long term capability (Schueler, 1987). An off–line sand filtration
system receiving runoff from a shopping mall and car park in Austin, Texas demonstrated
removal efficiencies for faecal coliforms, TSS and BOD of 76%, 71% and 70% respectively
(Austin City Dept. of Public Works, 1986). Metal, nutrient and hydrocarbon removal efficiencies
were less encouraging ranging between 45%–50%, 10%–35%, and 5%–48%. Urbonas et al ,
(1996) have reported cumulative TSS removal rates declining by 70% within one year of
installation for sand filter basins with flow–through rates being throttled from an initial one
metre/hour to less than 0.02m/hour causing frequent and severe flow bypassing. Ellis (2000) has
86

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

also described an infiltration system in Luton, Bedfordshire, receiving peak discharges of
2.4m 3 /s from a 26ha residential site, showing incremental annual accumulation of Zn, Cu and
Cd (averaging between 0.8mg/kg–1.5mg/kg for Zn) at all depths in the basin but with an
exponential mobilisation of soluble species with depth.
Schueler (1987) has claimed that infiltration basins have one of the highest failure rates (50%
within five years of installation) of all treatment systems currently in use in the US. Factors such
as lack of sediment pre–treatment, unsuitable soils, inadequate underdrainage and poor
maintenance have been cited as causes of failure. Norrstrom and Jacks (1998) found elevated
Cd, Pb, Cu, Zn and PAH concentrations in soils beneath an infiltration pond and although the
pollutant levels decreased with depth the Pb concentration exceeded the limit for drinking
water quality in the groundwater 4.5m below the soil surface. There is therefore a need, where
infiltration basins are used, to ensure that a regular and thorough maintenance strategy is
established. The current evidence would suggest that the best uses of filtration basins are as
final polishing systems in which the major treatment function is achieved by a preceding
sedimentation or biofiltration system which in turn is fitted with a front–end oil/sediment trap.
Although the use of infiltration basins has been recommended in Germany (Lange, 1990), their
use in the UK is limited due to the high costs of construction and maintenance in relation to
their pollutant removal abilities (Luker and Montague, 1994).

4.6.4 Storage facilities
Storage facilities that have been used for the treatment of highway runoff include sedimentation
tanks and chambers and detention or retention ponds and basins as well as wetlands.
Sedimentation tanks and chambers are artificial structures that may be built underground to
reduce their visual impact. In contrast, ponds, basins and wetlands can all be defined as
sustainable urban drainage systems which can be designed to create wildlife habitats and to
enhance the aesthetic aspects of the highway environment. One requirement of all these
systems is to store the received storm water prior to releasing it at an appropriate rate once the
peak flow has passed. Both on–line and off–line systems can be employed with the former
usually being created by enlarging the existing watercourse. The main quality improvements in
non–vegetated systems are provided by the increased sedimentation that occurs in the relatively
still conditions produced by the large storage capacity. Detention basins are essentially
designed to provide flow attenuation but by increasing the detention time by up to 24 hours
(extended detention ponds), the potential for removal of some of the fine suspended solids is
improved. Retention ponds are permanent water bodies that are designed to provide increased
runoff storage times and hence offer increased treatment through the settlement of finer particles
and also biodegradation of relevant pollutants. Vegetated systems (wetlands) can provide the
same level of treatment but over shorter periods of time and often at the expense of
incorporating an equivalent storage capacity.
4.6.4.1 Storage tanks/chambers
The percentage removal efficiencies from an experimental study in which a 1500l sedimentation
tank was located adjacent to the M1 motorway are shown in Box 4.5. The limited pollutant
removal capabilities together with the size constraints (estimated required volume of 60m 3 to
provide 100% theoretical solids removal from runoff from a one kilometre length of a three lane
highway) and the safety factors associated with large open tanks next to busy roads do not
encourage the use of these systems. The relatively poor treatment efficiencies found in the UK
study have been supported by French motorway studies (Ruperd, 1987) in which removals of
36%, 38%, 61%, 48% and 22% were obtained for COD, BOD, TSS, total lead and nitrate
respectively. A disadvantage of sedimentation tanks is the high cost of regular maintenance
procedures. The conclusions of the M1 motorway study were that tank desludging would be
required at five yearly intervals.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

87

Pollutant
TSS
Pb tot
Zn tot
Zn diss
COD
Oil
PAH

Percentage removal efficiency
52
40
47
15
35
28
45

(after Colwill et al , 1984; Perry and McIntyre, 1986).

Box 4.5: Mean percentage annual removal efficiencies for a UK motorway sedimentation
tank treatment system.

4.6.4.2 Lagoons
Lagoons differ to sedimentation chambers in that they are constructed by excavating natural earth
basins which can be covered with vegetation and which may be lined where it is necessary to
prevent infiltration. The predicted pollutant removal performances of a sedimentation lagoon are
shown in Table 4.3. In addition to sedimentation processes for particulate associated pollutants,
soluble pollutants can be removed by filtration and adsorption on vegetation. Stotz (1990)
investigated a lagoon operating in both dry and wet modes when receiving runoff from a German
highway. There were increases in the removal efficiencies of TSS (45%–54%), COD (18%–39%),
Pb and Cd when the lagoon was operating under wet conditions. Regular maintenance is
essential to retain the long–term effective performance of sedimentation lagoons with the
maintenance frequency being dependent on the storage provision made for silt.
4.6.4.3 Extended detention basins
Extended detention basins are dry, naturally vegetated impounding systems which are dry
during normal conditions but provide storage of storm runoff during periods of heavy rainfall. A
liner or membrane may be incorporated into the design if it is essential to avoid infiltration to
groundwater. The maximum depth of water should not exceed three metres and the basin should
be constructed with shallow side slopes (no steeper than 1:4) to allow access for maintenance.
If the basin is on–line, an overflow structure will need to be provided to deal with very large
storms and to ensure that a minimum freeboard of 0.5m is maintained. Associated with their
flow attenuation characteristics, detention basins also encourage sedimentation of the coarser
suspended materials although fine solids will be re–suspended during high flows. They also
demonstrate low removal efficiencies for soluble pollutants (see Table 4.2). Ideally, an extended
detention pond should be designed to fully contain the design treatment volume and to allow
this to be discharged through the outlet control structure over a period of at least 24 hours.
The long–term performance of extended detention basins requires the provision of an upstream
or inlet settling basin or forebay (12%–20% of the total basin area) to capture coarse sediment
loads. Sediment traps should have “shut–off” facilities to contain spillages. The inlet structure
should also incorporate energy dissipation to reduce turbulence with flow velocities of less than
0.25m/s being recommended to prevent particle re–suspension from sediment pre–treatment
facilities. Maintenance procedures should involve regular inspection of the inlet and outlet
structures and safe removal of collected sediments at intervals of between seven and ten years.
On–site bunded facilities for the de–watering of the contaminated sediments may also be
necessary and final disposal may need to be to a scheduled landfill site.
88

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Stahre and Urbonas (1990) have quoted long term efficiencies for extended detention basins
having 48 hour detention times of 50%–70% for TSS and hydrocarbons, 20%–40% for BOD,
75%–90% for Pb and 30%–60% for Zn. Lower detention times of four to ten hours provide up
to 50%–60% TSS removal but as most dry basins often have less than two hours detention times,
the pollutant removal efficiencies are usually rather mediocre with TSS in the range of
15%–20% and BOD/COD generally less than 10%. A recent study concerning runoff from the
London Orbital M25 motorway has indicated high removal efficiencies (84%–95%) for a range
of 11 metals by a 500m 2 detention pond preceded by a grit trap and an oil interceptor (Hares
and Ward, 1999).
4.6.4.4 Retention basins
Retention
basins
(or
balancing ponds) contain a
permanent pool of open
water (maximum depth two
metres to three metres;
surface area equivalent to
one percent of the total
contributing area) around
which edge planting of
emergent
macrophyte
vegetation
may
be
introduced. Such planting
assists in the treatment
process
by
providing
biological
removal
of
Vegetation balancing pond adjacent to the Newbury Bypass.
pollutants, particularly those
in the dissolved phase. This reinforces the removal of particulate associated pollutants through
sedimentation within the relatively still water body, which should be sized to contain at least
four times the treatment volume in order to provide maximum retention. The inlet and outlet to
the pond should be situated so as to reduce the possibility of short–circuiting which is also
assisted by designing the system with flow path length to width ratios of at least 3:1. Full design
detail for retention (balancing) ponds is provided in Hall et al (1994) who advocate the fitting
of a sediment forebay (or upstream sediment trap or diversion structure) to maximise pollutant
removal efficiencies and extend operational lifetimes. Retention basins can be readily adapted
to provide temporary storage in the event of accidental spillage by installing isolation devices
at the outlet.
From a study of nine retention ponds in the Florida area, Yousef et al (1994) have recommended
the need to remove sediments every 25 years, based on monitored accumulation rates, and to
protect groundwaters from potential contamination from elevated heavy metal levels. Copper,
Pb and Zn accounted for over 75% of the heavy metal sediment content with average
accumulation rates of 1.3 kg/ha yr, 13.8 kg/ha yr and 6.9 kg/ha yr (Yousef et al , 1996). Similar
elevations of sedimentary heavy metal levels have been observed in French studies of retention
basins (Lee et al , 1997). It is clear that, in all cases, detention ponds require regular inspection
and maintenance.
4.6.4.5 Constructed Wetlands
Wetlands (both natural and constructed) have been widely used for the treatment of sewage and
for urban, industrial and agricultural runoff (Cooper and Findlater, 1990) but experience of their
use for highway runoff is relatively limited. The potential pollutant removal capabilities are
based on a number of mechanisms including biofiltration, sedimentation, adsorption, biological
uptake and physico–chemical interactions. The widely used designs of constructed wetlands are
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

89

surface flow and sub–surface
flow systems. Comparison of
these two designs shows that
the construction costs of
sub–surface systems are
higher due to the cost of the
substrate media and the inlet
distribution system. They are
also more difficult to
maintain
but
these
disadvantages are considered
to be balanced by their
increased treatment potential
(Ellis et al , 1994).

Constructed wetland adjacent to the Newbury Bypass.

Box 4.6 indicates the average range of pollutant removal efficiencies that have been reported in
the literature for constructed wetlands receiving highway runoff in the UK, France, Canada and
the US. The variability in performance noted in Box 4.6 has been attributed to short–circuiting,
short detention and contact times, pollutant remobilisation, and seasonal vegetation effects
(Strecker et al , 1992). A recent study (Hares and Ward, 1999) has found elevated metal removal
efficiencies of consistently around 90% for a combination of a 3900m 2 wet biofiltration pond
and a 1000m 2 sedimentation pond receiving motorway runoff.
Wetland Type

TSS

Faecal
Ntot
Coliforms

Ptot

Pbtot

Zntot

BOD/TOC

Subsurface Flows

85
(67–97)

88
(80–97)

44
(25–98)

50
(20–97)

83
(5–94)

42
(10–82)

–

Free Surface
Flows

73
(13–99)

92
86–99)

33
(10–99)

43
(2–98)

69
(41–83)

58
(31–75)

15
(5–32)

Box 4.6: Percentage pollutant removal rates in constructed wetlands.
In the absence of established design criteria for constructed wetlands for the treatment of road
runoff, Shutes et al (1999) have made a number of recommendations and Ellis (1999) has
described a kinetic sizing approach. Ideally, the constructed wetland should be able to treat
storms with a return period of ten years. However, in the case of sub–surface systems, it may be
practical to ensure that the first flush containing the heaviest pollution loads receives adequate
treatment. Hydraulic retention time is a very important factor in the treatment performance of
constructed wetlands. Considerations affecting this include the aspect ratio (width:length), the
vegetation, substrate porosity and hence hydraulic conductivity, depth of water, and the slope
of the bed. An ideal design should retain the average annual storm volume for 10–15 hours to
achieve a good pollutant removal efficiency. A preferred retention time would be 24–36 hours
if satisfactory bacterial and soluble metal removal efficiencies and fine solids settlement are
required.
The design of the inlet to the constructed wetland should ensure that the influent is evenly
distributed across the width of the bed with flow velocities not exceeding 0.3m/s to 0.5m/s to
allow effective sedimentation and to prevent physical damage to the plants. High water flows
can be dissipated by the incorporation of a stilling structure, such as one metre wide stone
trench (rip–rap or gabion), immediately following the inlet pipe. The optimal hydraulic loading
to the constructed wetland should not exceed one m 3 /m 2 .d to assist satisfactory treatment. A
90

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

concern with wetlands is the possibility of the plants being deprived of water during prolonged
dry periods and to counteract this the outlet structure should be set to maintain a water level
which is not lower that 300mm below the substrate surface. A substrate depth of at least 600mm
is recommended for sub–surface wetlands to allow sufficient rooting depth for species such as
the common reed ( Phragmites australis ). The other widely used plant species is reedmace ( Typha
latifolia ) and it has been recommended that these two species are ideally suited to the treatment
of highway runoff in constructed wetlands (Shutes et al , 1999).
The ideal constructed wetland treatment system for highway runoff would incorporate the
following cellular structures arranged in series; oil separator and silt trap; spillage containment;
settlement pond and associated control structures; constructed wetland and associated control
structures; final settlement pond; and outfall into receiving watercourse. In addition, full access
would be required for the necessary maintenance activities. These will include sediment
removal from the initial and final settlement ponds and the control of weeds in the early stages
of plant growth. It is envisaged that after periods of 15 to 25 years of operation, the
contaminated substrate within constructed wetlands will require cleaning or replacement to
regenerate the hydraulic conductivity and pollutant removal capacity of the system.

4.6.5 Alternative road surfacings
A number of alternative forms of hard–standing surface constructions have been developed to
reduce the environmental impact of increasing traffic densities. The designs include continuous
surfaces (such as porous macadam) and porous or solid blocks separated by open joints or
castellated “grasscrete” blocks with their central voids filled with soil or gravel.
4.6.5.1 Porous Paving
Porous paving consists of hollow concrete surfacing materials which allow runoff to infiltrate
through pore spaces within the matrix of the material into the sub–base, the nature and depth
of which will depend on traffic density. The surfacing allows the immediate infiltration of
rainfall–runoff with the sub–base providing storage, treatment and pathways for downward
percolation into the underlying soil or to perforated underdrains. Infiltration rates should
normally exceed 1000mm/hour and Pratt (1995) has observed mean infiltration rates of
2600mm/hour on a concrete block surfacing six years after installation without any
maintenance.

❍ Interception and filtering of “first–flush” solids and solid-associated pollutants. Pratt et al
(1995) have shown that TSS can be reduced by between 63%–98%, COD between
36%–85% and Total Oil by 72%–98% with total oil retention and biodegradation varying
between 650–916 g/m 2 /year. Pollutants are effectively trapped in the upper layers of the
construction thus minimising their throughput.
❍ Surface runoff can be completely avoided and total flow volumes from the site reduced
by between 20%–45% by retention within the pavement reservoir.
❍ Percolation through to groundwater supports natural recharge.
❍ Reduced requirement for grit and salt applications during icy winter periods as the surface
is freely draining.
❍ Elimination of kerbs and gutters.
❍ Improvements in traffic safety because of enhanced skid resistance and better visibility on
wet pavements.

Box 4.7: Advantages of porous paving.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

91

The specific advantages of porous paving are outlined in Box 4.7. It has excellent potential for
use in driveways, residential cul–de–sacs, vehicle parking and service areas and can possess a
load–bearing strength and longevity similar to conventional pavement. A 1500m 2 porous paved
car park in Edinburgh, although costing 15% more than conventional “blacktop” asphalt, has
shown significant attenuation of the outlet hydrograph with first discharges only occurring
several hours after the start of rainfall. In addition, TSS, COD and BOD outflow values were
consistently below 20mg/l, 10mg/l and 2mg/l respectively with hydrocarbons below detection
levels. Pratt et al (1999) have also shown that pilot scale permeable pavement performed as an
effective in situ aerobic bioreactor reducing petroleum contamination in the effluent to 2.4% of
that applied. The results of these and similar studies elsewhere in Scotland have led SEPA to
accept that oil interceptors are not required on permeable car parking areas which have an
approved engineering sub–base. However, a minimum six–monthly 'brush and suction' cleaning
is recommended in order to maintain the performance efficiency of the porous paving surface.
Grasscrete type modular pavement is well suited to car parks and possesses infiltration rates
(0.2mm/s to 1.0mm/s) which are well in excess of most design storm rainfall intensities.
Filtration–sedimentation and adsorption processes within the structural reservoir of the
surfacing material can limit TSS outflows from near zero to 50mg/l and typically remove
between 40%–60% bacteria, 70%–90% heavy metals and hydrocarbons. Pre–cast pavers over
lattice slabs offer the dual advantages of on–site infiltration and easy maintenance. The
inevitable accumulation of silt in the surface layers of the “reservoir” construction and
“clay–bridging” between particles during wetting–drying cycles can lead to clogging and failure
of the structure although minimum lifetimes for properly installed and maintained structures can
be of the order of 10 to 15 years.
4.6.5.2 Porous Asphalt
Porous asphalt (or macadam) pavements consist of an open–graded asphalt mix
(powdered/crushed stone with a bitumen binder) with a coarse surface texture and a high void
ratio. The open texture with continuous pore spaces allows rainfall to immediately infiltrate the
surface. It is usually laid some 50mm thick over new or existing impermeable road surfaces with
stormwater flowing laterally across the highway within the porous asphalt layer to the kerb or
to a filter drain. Further guidance on the design and application of porous asphalt surfacing can
be obtained from the 1994 DoT Design Manual for Roads and Bridges Volume 7, Section 1 (3).
Because of the shallow crossfall gradients and the amount of fine silt present on highway
surfaces, the pore spaces within the asphalt often block within five years except where the
passage of vehicle tyres “pump” the pores clear of silt. Porous asphalt surfacing has become
popular because it forms a highway surface which generates less vehicle noise; reduces splash
and spray and hence also reduces aquaplaning whilst enhancing driver visibility; and provides
a durable, high–speed road surface. The pollutant removal capabilities of porous asphalt have
been investigated by Stotz and Krauth (1994) who found that yearly filterable solids were 50%
lower than in the drainage leaving impervious surfaces and that mineral oil and PAH’s were
detained more efficiently. Legret and Colandini (1999) have demonstrated the ability of porous
asphalt to retain heavy metals with removal efficiencies of 84%, 77% and 73% for Pb, Cd and
Zn respectively.

4.7 Recommendations
The selection of a particular type or combination of controls for the management and treatment
of highway runoff will depend very much on the local and site circumstances. The final design
criteria will include consideration of the highway carrying capacity, the size and character of
the site drainage, the sensitivity of the receiving surface and/or groundwater (in terms of both
flow volumes and quality), landscaping and planning concerns in addition to normal safety,
operational and maintenance requirements. Weighted evaluation of these characteristics will
92

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Treatment
Device

Capital Cost
(£’000s)

Maintenance Cost
(£/per yr)

Comments

Gully/Carrier
Pipe System

150–220

1000

No fin drainage
allowed for in costs

Filter/
French Drains

160–180

–

Requires replacement
after 10–12 years

Grass Swale

15–40

350

With no off–site
disposal of cuttings

Oil Interceptors
(with grit chamber)

8–30

300–400

Sedimentation Tank

30–80

300–350

Sedimentation
Lagoon/Basin

45–100

500–2000

Infiltration
Trench/Basin

20–50

2000–2500

Requires infill
replacement every
5–10 years

Retention
(Balancing) Basin

15–300

350–1000

With no vegetation or
off–site dewatering and
disposal of sludge and
cuttings

Wetland Basin

15–160

2000–2500

Annual maintenance
for first 5 years. (declining
to £800–£1000 p/yr
after 3 years)

Combined
Treatment–Train
System

100–300

2000–3000

Assume grass swale,
oil/grit interceptor,
sediment forebay and
wetland cells

Table 4.4: Capital and Maintenance Costs for Highway Treatment Systems.
indicate which types of techniques and what level of expenditure can be justified for the
particular site. Such an evaluation could take place withn the framework of the highways
environmental management model outlined in Chapter 3 (section 3.9).

4.7.1 Costings
There is very little data available on the relative costs of differing treatment systems to remove
pollutants from highway runoff. Such costs will vary between sites depending upon local
conditions and because of:
❍ engineering constraints – site access, topography and size; lining requirements;
construction techniques; and
❍ land constraints – legal and land purchase costs; access provision; the size, type and
layout of treatment devices.
In general terms, engineering constraints will tend to increase the design costs whilst land
constraints will decrease costs but at the same time reduce performance. Table 4.4 provides a
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

93

94

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

4

Infiltration

Soakaway

4

2

4

3

4.5

2

4

4

4.5

5

4.5

5

4

2

4

1.5

0

0

4

1

3

1.5

2

1

–4.5

–3

–4

–3

–5

–4

–4

–4

–4

–3.5

–3

–2

–4

–3

–5

–3

–1

–2

–5

–4

–2

–3

–4

–2

to Site
Conditions

Sensitivity

Volume

O&M

Reduction

Runoff

–5

–2

–5

–2

–1

0

–4

–1

–2

–1

–1

–2

Pollution

Groundwater

Potential for

–5

–2

–4

–2

–2

–3

–4

–3

–2

–1

–1

–2

Potential

Failure

Overall

Table 4.5: An Assessment of the Overall Effectiveness Potential of Treatment Systems for Highway Runoff.

2

4

Filter Strip

Trench

2

1

4.5

4

4

3.5

4

5

3

Grass Swale

Pipe System

Gully/Carrier

Interceptor

Oil/Grit

Basin

Infiltration

Lagoon

Sedimentation

Pavement

Porous

Basin

(Balancing)

Retention

Basin

Wetland

Basin

Detention

(Dry)

Extended

Quality Control

Facility

Flow Rate

Water

Treatment

2

2

3

3

3

2

3

3

4

4

4

4

Hydraulic

2

1

3

1

1

2

4

3

3

4

4

3

Quality

Water

Design Robustness

–2.5

–0.11

0.00

0.06

0.06

0.17

0.22

0.33

0.89

1.22

1.17

1.11

Averages

Rating

12

11

10

8

8

7

6

5

4

3

2

1

Order

Rank

first–order cost estimation of the ranges of capital and maintenance costs associated with
various treatment systems although the combined use of individual devices in a
“treatment–train” would give reductions of about 20%–25% in overall costings. The costs are
based on a one kilometre length of six lane motorway and some scaling–down would be
required for major roads and other highways. The large range in costings shown for some
treatment systems largely reflects local sizing requirements for particular devices that can
particularly influence for example, the final costs of retention basin and wetland systems.

4.7.2 Design selection
The choice of a particular treatment design will be dependent on an iterative procedure
reviewing the possible options to meet the combined needs of traffic flows, expected runoff
rates/volumes, water quality risks and any specific safety and amenity considerations. Details of
the performance efficiency of individual treatment devices have been given in Section 4.6 and
Table 4.3 provides a reference summary of the general efficiency and value of the various
treatment facilities for ease of comparison. The table also gives some indication of the design
robustness in terms of the system performance. However, no single device is likely to be as
effective as an in–series “treatment–train” and whenever possible, best practice should utilise
appropriate combinations of containment and treatment and wherever feasible low cost
technology options, for example, vegetative systems. This approach would be particularly
suitable for rural highways. The apparent high variations noted in performance efficiency for
individual pollutant parameters implies that many uncertainties exist in how particular designs
will perform over time. Table 4.5 is an attempt to provide a more detailed evaluation of the
effectiveness potential of various treatment devices with both positive (1 up to 5) and negative
(–1 down to –5) aspects being considered. For example, potential for failure is considered to be
a negative feature whilst the potential for mitigating increases in surface runoff volume is
considered to be a positive aspect. It is recognised that the rankings are somewhat subjective
being based on information collated from the literature and on personal experience and in
addition, the individual parameters are unweighted. However, the composite average rating
scores provide a ranking derived from the integration of all design considerations and the scores
can be adjusted (and parameters weighted) to suit local conditions.
As stated in Section 4.5.6, the various UK regulatory authorities are seeking to minimise the
deleterious impacts of impermeable surface runoff through the introduction of source control
techniques. A screening methodology for the initial assessment of the suitability of such source
control methods has been developed (Thomas and Robinson, 1997; Ellis, 2000) and Figure 4.3
adapts this approach for highway discharges. The acceptability matrix (which accords with the
Environment Agency PPPG; see Section 4.5.4) should be used as an initial indication of
treatment options in conjunction with the appropriate EA groundwater vulnerability maps and
EA surface water RE designations (see Section 4.5.2 and Figure 4.2). However, site specific
assessments will be needed prior to the final selection of a treatment option.
The simplified hierarchy of
source treatment options
summarised
in
the
acceptability
matrix
(Figure 4.3) is primarily
intended for application to
urban receiving waters and
may be over rigorous if
applied
to
rural
environments. Potential
impacts for discharges to
surface waters have been
quantified in the matrix
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

<5,000
5,000 - 15,000
>15,000

AADT
<5
S
M
M

Dilution Ratio
5 – 20 >20
L
L
S
L
MS

L; Low Potential Impact
S; Significant Potential Impact
M; Major Potential Impact

Box 4.8: Surface water impact criteria.
95

into three categories; Low (L), Significant (S) and Major (M) Impacts. The basis for these impact
categories are defined in terms of annual average traffic densities (AADT) and/or receiving water
dilution ratios (see Box 4.8). The impact categories cannot be strictly adhered to as other factors
also influence the receiving water sensitivity including the ecological status and physical
characteristics but the categorisation provides some initial guidance which can be checked
against field surveys. Site specific surveys will also be required for discharges to surface waters
using the approaches recommended in Volume 11 of the Design Manual for Roads and Bridges
(DETR, 1998).

4.7.3 Principal recommendations
Proposed priority of recommendations
1. The pollutant removal potentials of different treatment systems are still not fully understood
and therefore a co–ordinated monitoring strategy should be introduced to enable treatment
efficiencies to be determined under the full range of relevant hydrometeorological conditions.
This strategy should be agreed between the relevant controlling authorities and agencies.
2. To achieve optimum pollutant removal efficiencies from highway runoff prior to discharge to
receiving waters, careful consideration should be given to the choice and design of treatment
systems. An appropriate treatment system or combination of treatment systems should be
selected to provide the most satisfactory performance with respect to the pollutants of concern
at a particular location. Modular approaches can be incorporated into new developments and
also be retrofitted to existing highway drainage systems. Where “treatment trains” are utilised,
they should include low technology approaches, such as swales, and the option to fully treat
the polluted “first flush” should be adopted where treatment storage capacity is a concern.
3. A better definition of threshold toxicities, both acute and chronic, in receiving waters due to
highway discharges would be beneficial. This should relate to identified highway pollutants and
the factors which control their build-up on and removal from road surfaces, such as traffic
density, antecedent dry period, dilution ratios and so on.
4. There is a need for the careful monitoring of any water contaminants moving within the
unsaturated zone down gradient of major infiltration systems and soakaway fields. This is
required to establish long-term knowledge of the quality of water moving to aquifers and
particularly where the source of the contaminated water is highway runoff.
5. Groundwater Source Protection Zones (SPZs) need to be quantified in terms of dynamic
aquifers where fissure flow dominates as current 2D steady state modelling (FLOWPATH) is
inappropriate given its sensitivity to transmissivity, effective porosity and storage.
6. The regular inspection and maintenance of all treatment components is essential and ideally
this should be in accordance with an agreed protocol following the installation of a treatment
system. This is particularly important for all treatment systems involving infiltration
7. A thorough assessment of the risk associated with accidental spillages should be carried out
(for example, using the Design Manual for Roads and Bridges ) particularly in relation to
identified “hotspots” that is, those outfalls where the greatest risk to the receiving water
environment is perceived. Also with regard to spillages, integrated and responsive actions
between the appropriate agencies should be developed. Where possible, integrated approaches
to the treatment of both routine runoff and spillage should be provided.
8. The overall treatment role of gully pots is still uncertain and because pollutant release is
possible following sediment accumulation, regular monitoring is essential to identify citicial
build–up locations. Where gully pots are used in highway drainage systems a reduction in
96

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

numbers is recommended and, where possible, the use of alternative systems involving in-situ
bioremediation should be investigated.
9. The problems associated with the use of de–icing salt have been highlighted in this Chapter.
It is essential that this is used carefully and wisely so as not to leave excessive deposits on
highway surfaces. The use of alternative de-icing agents, such as calcium magnesium acetate,
should be fully investigated.
10. The application of herbicides to highway environments for weed control should only be
used after a full assessment of the impact on adjacent surface waters and groundwaters has been
made. Application rates should be carefully controlled and, where possible, the timing of
application arranged to coincide with extended dry weather periods

References
Amrhein C, Mosher PA,
and Strong JE, 1993

Colloid–assisted transport of trace metals in roadside soils
receiving deicing salts. Soil Science Society of America
Journal, 57(5), pp1212–1217.

Austin City Department of
Public Works, 1986

Design Guidelines for Water Quality Control Basins.
Watershed Management Division, Austin, Texas, US.

Barbosa AE and
Hvitved–Jacobsen T, 1999

Highway runoff and potential for the removal of heavy metals
in an infiltration pond in Portugal. Science of the Total
Environment, 235 (1–3), pp151–159.

Barrett ME, Walsh PM,
Malina, J F and
Charbeneau RJ, 1998

Performance of vegetative controls for treating highway
runoff. Journal of Environmental Engineering–ASCE, 124(11),
pp1121–1128.

Boxall ABA and Maltby L, 1995 The characterisation and toxicity of sediment contaminated
with road runoff. Water Research, 29(9), pp2043–2050.
BRE, 1991

Soakaway Design. BRE Digest 365, Building Research
Establishment, Watford, UK

Bris FJ, Garnaud S, Apperry,
N, Gonzalez A, Mouchel JM,
Chebbo G and Thevenot DR,
1999

A street deposit sampling method for metal and hydrocarbon
contamination assessment. Science of the Total Environment,
235(1–3), pp211–220.

British Standards Institution,
1983

Code of practice for drainage of roofs and paved areas.
BS6367:1983, London.

British Standards Institution,
1991

Specification for salt for spreading on highways for winter
maintenance. BS3247:1991, London.

Butler D and
Karunaratne SHPG, 1995

The suspended solids trap efficiency of the roadside gully pot.
Water Research, 29(2), pp719–729.

Butler D and Memon FA,
1999

Dynamic modelling of roadside gully pots during wet
weather. Water Research, 33 (15), pp3364–3372.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

97

98

CIRIA, 1998

Management of Gully Pots for Optimum Runoff Quality.
Report No 183. Construction Industry Research Information
Association.

CIRIA, 2000a

Sustainable Urban Drainage Systems – design manual for
Scotland and Northern Ireland. Report No C521.
Construction Industry Research Information Association.

CIRIA, 2000b

Sustainable Urban Drainage Systems – design manual for
England and Wales. Report No C522. Construction Industry
Research Information Association.

Colwill GM, Peters CJ and
Perry R, 1984

Water quality of motorway runoff. Transport and Road
Research Laboratory Supplementary Report No. 823,
Crowthorne.

Cooper PF and Findlater RC,
(Eds), 1990

Constructed Wetlands in Water Pollution Control. Pergamon
Press, Oxford, UK.

Council of the European
Communities, 1980

Directive of 15 July 1980 relating to the quality of water
intended for human consumption. 80/778/EEC; OJL 229, 30
August 1980.

DETR, 1998

Design Manual for Roads and Bridges. Volume II, Section 3,
Part 10. Department of the Environment, Transport and the
Regions, London.

Department of Transport,
1991

Design Manual for Roads and Bridges. DoT, London.

Department of Transport,
1992

Trunk road maintenance manual. Volume 2, Part 3. Routine
and winter maintenance code. Department of Transport,
London.

Dierkes C and Geiger WF,
1999

Pollution retention capabilities of roadside soils . Water
Science and Technology, 39(2), pp201–208.

EA, 1998

Policy and Practices for the Protection of Groundwater.
Environment Agency, Bristol.

Ellis JB, 1979

The nature and sources of urban sediments and their relation
to water quality . pp199–216 in G E Hollis (editor): Man’s
impact on the hydrological cycle in the UK. GeoAbstracts
Ltd., Norwich.

Ellis JB, 1993

Achieving standards for the recreational use of urban waters.
155–173 in D Kay and R Hanbury (Edits): Recreational water
quality management. Ellis Horwood Ltd, Chichester.

Ellis JB, 1999

The use of vegetative controls for the treatment of highway
discharges. pp357–363 in Ellis, J B (Edit): Impacts of Urban
Growth on Surface and Groundwater Quality. Publication
No. 259, IASH Press Ltd, Wallingford.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Ellis JB, 2000

Infiltration systems: A sustainable source control option for
urban stormwater quality management. Journal of the Institute
of Water & Environmental Management, (In Press).

Ellis JB and Revitt DM, 1989

Traffic related pollution on highway surfaces. Urban Pollution
Research Centre Research Report No. 18, Middlesex
University.

Ellis JB and Revitt DM, 1991

Drainage from roads: Control and treatment of highway
runoff. Report NRA 43804/M1D.012, Thames NRA, Reading.

Ellis JB, Revitt DM and
Llewellyn N, 1997

Transport and the environment: Effects of organic pollutants
on water quality. Journal of the Chartered Institute of Water &
Environmental Management, 11(3), pp170–177.

Ellis JB, Revitt DM,
Shutes RBE and Langley JM,
1994

The performance of vegetated biofilters for highway runoff
control. Science of the Total Environment, 146/147,
pp543–550.

Hall MJ, Hockin DL
and Ellis JB, 1994

The Design of Flood Storage Reservoirs.
Butterworth–Heineman Ltd, London, UK.

Hares RJ and Ward NI, 1999

Comparison of the heavy metal content of motorway
stormwater following discharge into wet biofiltration and dry
detention ponds along the London Orbital (M25) motorway.
Science of the Total Environment, 235 (1–3), pp169–178.

Irish LB, Barrett ME, Malina JF
and Charbeneau RJ, 1998

Use of regression models for analysing highway storm water
loads. Journal of Environmental Engineering–ASCE, 124 (10),
pp987–993.

Jacobs JL and Ellis JB, 1991

Bacterial water quality in urban receiving waters. Water
Science and Technology, 24, pp113–116.

Knight RL, Adams R,
O’Brien C and Davis ER, 1998

Beltway 8 Wetland Water Quality Project–Constructed
wetlands for storm water polishing and wetland mitigation
banking. Transportation Research Record, 1626, pp11–20.

Lange G, 1990

The design and construction of treatment processes for
highway runoff in the FRG. Science of the Total Environment,
93, pp499–506.

Lee PK, Touray JC,
Bailif P and Ildefonse JP,
1997

Heavy metal contamination of settling particles in a retention
pond along the A–71 motorway in Sologne, France. Science
of the Total Environment, 201 (1), pp1–15.

Legret M and Colandini V,
1999

Effects of porous pavement with reservoir structure on runoff
water: water quality and fate of heavy metals. Water Science
and Technology, 39 (2), pp111–117.

Lord B, 1989

Program to reduce deicing chemical use. In: L A Roesner, B
Urbonas and M B Sonnen, Design of Urban Runoff Quality
Controls, American Society of Civil Engineers, New York,
pp421–435.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

99

100

Luker M and Montague K,
1994

Control of pollution from highway drainage discharges.
Report No. 142, Construction Industry Research and
Information Association, London. pp 152.

Marsalek J and Rochfort Q,
1999

Toxicity of urban wet–weather pollution sources : stormwater
and CSOs. In: Proceedings of 8th International Conference on
Urban Storm Drainage, Sydney, Australia. pp1575–1582.

Mikkelsen PS, Hafliger M,
Ochs M, Jacobsen P, Tjell JC
and Boller M, 1997

Pollution of soil and groundwater from infiltration of highly
contaminated stormwater – A case study. Water Science and
Technology, 36 (8–9), pp325–330.

Murfee GW, Scaief PE and
Whelan JM, 1999

Biodetention: A Best Management Practice for Non–Point
Source Pollution Control. In: Procedings of 3rd International
Conference on Diffuse Pollution. 95–99. Scottish
Environmental Protection Agency, Edinburgh.

Norrstrom AC and Jacks G,
1998

Concentration and fractionation of heavy metals in roadside
soils receiving de–icing salts. Science of the Total
Environment, 218 (2–3), pp161–174.

Novotny V, Muehring D,
Zitomer DH, Smith DW
and Facey R, 1998

Cyanide and metal pollution by urban snowmelt: Impact of
deicing compounds. Water Science and Technology, 38 (10),
pp223–230.

Perdikaki K and Mason CF,
1999

Impact of road runoff on receiving streams in Eastern
England. Water Research, 33 (7), pp1627–1633.

Perry R and McIntyre AE,
1986

Impact of motorway runoff upon surface water quality . In
Solbe, JF (editor) Effects of Land Use on Freshwaters. Ellis
Horwood Ltd, Chichester.

Pratt CJ, 1995

Infiltration drainage: Case studies of UK practice. Project
Report No.22, Construction Industry Research and
Information Association, London.

Pratt CJ, Mantle JDG and
Schofield PA, 1995

UK research into the performance of permeable pavement
and reservoir structures in controlling stormwater discharge
quantity and quality. pp337–344 in Proceedings of the 2nd
International Conference on Innovative Technologies in
Urban Storm Drainage, Graie, Lyon, France.

Pratt CJ, Newman AP
and Bond PC, 1999

Mineral oil bio–degradation within a permeable pavement:
Long term observations . Water Science and Technology, 39
(2), pp103–109.

Price M, 1994

Drainage from roads and airfields to soakaways: Groundwater
pollutant or valuable recharge? Journal of the Chartered
Institute of Water & Environmental Management, 8,
pp468–479.

Rendahl B and Hedlund S,
1991

Influence of deicing salts on motor–vehicle corrosion.
Materials Performance, 30 (5), pp42–44.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Revitt DM, Ellis JB and
Llewellyn NR, 1999

Herbicide behaviour in the runoff from an urban catchment.
In: Proceedings of 8th International Conference on Urban
Storm Drainage, Sydney, Australia. pp96–104.

Ruperd M, 1987

Efficacite des Ouvrages de Traitement des Eaux de
Ruisellement. Service Tech. L’Urbanisme, Div Equip
Urbains, Paris, France.

Physical characteristics of urban roadway solids transported
Sansalone JJ, Koran JM,
Smithson A and Buchberger SG, during rain events. Journal of Environmental
1998
Engineering–ASCE, 124 (5), pp427–440.
Sansalone JJ, Smitthson JA
and Koran JM, 1998

Development and testing of a partial exfiltration trench for in
situ treatment of highway drainage. Transportation Research
Record, 1647, pp34–42.

Sartor JD and Boyd GB, 1972

Water pollution aspects of street surface contaminants. Report
R2/72–081, US Environmental Protection Agency,
Washington DC.

Schueler T, 1987

Controlling Urban Runoff. Met Washington Council of
Governments, Washington DC.

Shutes RBE, Revitt DM,
Lagerberg IM and Barraud VCE,
1999

The design of vegetative constructed wetlands for the
treatment of highway runoff. Science of the Total
Environment, 235(1–3), pp189–198.

Stahre P and Urbonas B, 1990

Stormwater Detention for Drainage, Water Quality and CSO
Management. Prentice Hall, New Jersey.

Stotz G, 1987

Investigations of the properties of the surface water runoff
from Federal highways in the FRG. Science of the Total
Environment, 59, pp329–337.

Stotz G, 1990

Decontamination of highway surface runoff in the FRG.
Science of the Total Environment, 93, pp507–514.

Stotz G and Krauth K, 1994

The pollution of effluents from pervious pavements of an
experimental highway section: first results. Science of the
Total Environment, 146/147, pp465–470.

Strecker EW, Driscoll ED,
Shelley PE and Gaboury DR,
1992

Use of Wetlands for Stormwater Pollution Control. US
Environmental Protection Agency, Washington, DC.

Thomas J C and Robinson VK,
1997

A multi–functional surface water source control project.
pp671–676 in Chilton, J (Edit): Groundwater in the Urban
Environment, Balkema Publishing, Rotterdam.

Urbonas B, Duerfer JT and
Tucker LS, 1996

Stormwater sand filtration: a solution or a problem? APWA
Reporter, American Public Works Association, Washington
DC.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

101

102

Viklander M, 1996

Urban snow deposits–pathways of pollutants. Science of the
Total Environment, 189/190, pp379–384.

Viskari EL, Rekila R, Roy S,
Lehto O, Ruuskanen J and
Karenlampi L, 1997

Airborne pollutants along a roadside: Assessment using snow
analyses and moss bags. Environment Pollution, 97 (1–2),
pp153–160.

Walsh PM, Barrett ME,
Malina JF and Charbeneau RJ,
1997

Use of Vegetative Controls for Treatment of Highway Runoff.
Report No. 97–5. Center for Research in Water Resources,
University of Texas, Austin, Texas.

Wixtrom RN and Brown SL,
1992

Individual and population exposures to gasoline. Journal of
Exposure Analysis and Environmental Epidemiology, 2 (1),
pp23–78.

Wu JS, Allan CJ, Saunders WL
and Evett JB, 1998

Characterisation and pollutant loading estimation for
highway runoff. Journal of Environmental Engineering–ASCE,
124(7), pp584–592.

Yousef YA,
Hvitved–Jacobsen T, Sloat J
and Lindeman W, 1994

Sediment accumulation in detention or retention ponds.
Science of the Total Environment, 146/147, pp485–491.

Yousef YA, Baker, DM
and Hvitved–Jacobsen T, 1996

Modeling and impact of metal accumulation in bottom
sediments of wet ponds. Science of the Total Environment,
189/190, pp349–354.

Yu SL, Norris WK and
Wyant DC, 1987

Urban BMP Demonstration Project in the
Albemarle/Charlottesville Area. Final Report to Virginia
Department of Conservation and Historic Resources,
University of Virginia, Charlottesville, Virginia.

ZiebaPaulus J, 1998

Examination of used motor oils by flame AAS for criminalistic
purposes : a diagnostic study. Forensic Science International,
91(3), pp171–179.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

C HAPTER 5. A IR Q UALITY M ANAGEMENT
5.1 Introduction
In the UK, and most other developed countries, road traffic emissions are the largest single
source of a variety of common air pollutants. Most are emitted in the exhaust, but fuel
evaporation generates sizeable quantities of volatile organic compounds and particles are
produced by the abrasion of moving parts of the vehicles, such as tyres and brakes, and by wear
of the road surface. Legal limits for emissions were first introduced in the EU in the early 1970s,
and since then there have been two major and opposing influences on traffic pollution: new
vehicles have become less and less polluting, in response to the emission standards, but traffic
volumes have continuously increased (Box 5.1).
Road
traffic
produces
a
significant proportion of many
common air pollutants. The
example is for NO X , of which
about half is from road vehicle
exhaust. It is also responsible for
70% of CO, 40% of VOC, 25%
of PM 10 and 20% of CO 2 .

During the 1970s and 80s, total
NO X emissions increased despite
an overall reduction from
non–road
sources.
More
stringent emission standards for
road vehicles have now reversed
that trend. Now, road and
non–road
emissions
are
reducing.

Box 5.1: Some statistics and trends on road traffic emissions (based on Salway et al, 1999).
5.1a: NO x emissions.
Many of the compounds emitted by road vehicles are known or suspected to damage health if
their concentrations are high enough. In 1991, the Secretary of State for the Environment
established the Expert Panel on Air Quality Standards to consider the evidence on the health
effects of air pollutants and to recommend standards for ambient air quality. To date, they have
reported on benzene, ozone, 1,3-butadiene, carbon monoxide, sulphur dioxide, particles,
nitrogen dioxide, lead, and polycyclic aromatic hydrocarbons (Expert Panel on Air Quality
Standards, 1994 a,b,c,d; 1995 a,b; 1996; 1998; 1999). Road transport is a major source, directly
or indirectly, of all of these compounds except of sulphur dioxide. Other types of impact are
also important. Oxides of nitrogen and hydrocarbons take part in chemical reactions that
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

103

Although traffic volumes have
more than doubled since 1970,
emissions of carbon monoxide
from road traffic have fallen
significantly. This is mainly
because of the effectiveness of
more
stringent
emission
standards for cars. Over the
same period, the average rate of
emission for a new car has
reduced by 90%.

Box 5.1: Some statistics and trends on road traffic emissions (based on Salway et al, 1999).
5.1b: CO emissions.

produce acidic pollutants that can damage forests and freshwater ecology. Carbon dioxide is the
most abundant man–made greenhouse gas, and its increasing concentration in the atmosphere
is responsible for most of the enhanced global warming.
It is not surprising, then, that efforts have been made for many years to gain a better
understanding of the emission, propagation and impacts of vehicle pollutants and to develop
improved control methods. This chapter reviews the history of that process in the UK, examines
the current situation and looks forward to future developments.

5.2 The problem of air quality
5.2.1 Historical perspectives
The first formal procedure for assessing the environmental impacts of road schemes was
recommended by a committee chaired by Mr J Jefferson. They concluded, in 1976, that it was
not possible to include environmental factors in a formal cost–benefit analysis, but that a
standard format for their presentation should be used (Department of Transport, 1977).
Concerning air pollution, it was considered that lead concentrations were the most significant
factor, and could also be used to give an indication of other pollutants.
In 1977, a committee chaired by Sir George Leitch was asked by the Secretary of State for
Transport to review the procedures used for trunk road assessment. The committee’s terms of
reference were:

“to comment on, and recommend any changes in, the Department’s method of appraising trunk
road schemes and their application, taking account both of economic and environmental
factors, and of the extent to which these methods give a satisfactory basis for comparison with
investment in alternative methods of transport; and
“to review the Department’s method of traffic forecasting, its application of the forecasts and to
comment on the sensitivity of the forecasts to possible policy changes.”
104

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

As a result of their review, the committee proposed a standard framework for the assessment of
trunk road schemes (Advisory Committee on Trunk Road Assessment, 1977). They intended that
the framework should be generally comprehensible to the public, that groups and individuals
should be easily able to see how they would be affected, that it should comprehensively address
all the effects of the scheme and that it should balance costs and benefits in a rational manner. They
identified the five groups, and the ways in which they might be affected, as shown in Box 5.2.
Their conclusion on air pollution was:

“As well as its pure nuisance value, air pollution has the added and more serious disadvantage
that it may prove a permanent health risk to those constantly exposed to it. It is unlikely to be
a serious problem in the rural context. Where air pollution is likely to be a problem we
recommend that a special air quality report be prepared. Otherwise it should be excluded from
the assessment.”
While this was helpful in clarifying the basic requirements it raised a major problem. Who
would determine whether air pollution was likely to be a problem, and how would they reach
their decision?
The framework approach recommended by the Leitch Committee was adopted, and formalised
in a Departmental Standard on “frameworks for trunk road appraisal” (Departmental Standard
TD/8/80) and an Advice Note on “the preparation of frameworks for trunk road appraisal”
(TA/7/80), both issued in 1980. These documents were supported by the Manual of
Environmental Appraisal (MEA, Department of Transport, 1982) which gave guidance on
methods of assessing a scheme’s potential impacts on noise, visual impact, air pollution,
community severance, agriculture, heritage and conservation areas, ecology, disruption due to
construction, pedestrians and cyclists, the view from the road and driver stress. The section on
air pollution impacts attempted to address the Leitch requirement (for an air quality report
where a problem was likely) by providing a method to indicate whether pollution was likely to
be of concern.

Road users directly affected by the scheme who are concerned over the whole network to
reduce accidents, save time and vehicle operating costs, and perhaps to increase their
general comfort and the attractiveness of the view from the road.
Non–road users directly affected by the scheme including occupiers of land and buildings
adjacent to the route, whose objective is to minimise the environmental disadvantages it
might entail whilst ensuring that any associated benefits are maximised. For example, this
group clearly includes those on a route which is by–passed and affected by reduced traffic
flows as a result of a scheme.
Those concerned with the intrinsic value of the area through which the scheme passes whose
concern is that it should disturb that area as little as possible or in some cases – for example
an area of industrial dereliction – actually enhance it.
Those indirectly affected by a scheme whose concern is with its general land use effects,
with resource consumption, with its effects on other modes of transport and on business
initiatives.
The financing authority whose objective in this context is to ensure that the best possible
programme is completed at the least net cost to public funds

Box 5.2: Groups of individuals affected by a road scheme.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

105

For this purpose, a problem was defined as exposure more than once a year to an 8–hour
average concentration of carbon monoxide greater than 9 ppm, in accordance with the US
National Ambient Air Quality Standard. As was the case for lead, it was considered that carbon
monoxide would provide a reasonable indication of other traffic derived pollution. A graph was
provided that showed the carbon monoxide concentration as a function of the distance from a
road carrying 1000 veh/h at a speed of 100 km/h, and this concentration was corrected for the
actual flow and speed.
The MEA procedure was used for a number of years, but during that time changes took place in
the characteristics of traffic pollution, in the understanding of its effects on health and the wider
environment, and in its perception by the public and politicians as well as the scientific
community.
In the 1970s and 80s, the traffic pollutant that caused the greatest concern and controversy was
lead. Lead additives have been used for many years to improve the combustion properties of
petrol and result in the emissions of lead compounds in the form of fine particles. Research was
suggesting that lead could cause behavioural problems at low levels, especially in young
children, and the Government embarked on a programme of phased reductions in the maximum
lead content of petrol. Unleaded petrol became commercially available in 1987, and it was
required that all new cars registered after 1 April 1991 should be able to use unleaded petrol.
Since January 2000, with very limited exceptions, its use has been banned in EU countries.
The result of these changes in policy and regulations is that concentrations of lead in air no
longer approach the most recent health standards, which are themselves substantially lower
than their predecessors (EPAQS, for example, recommended an annual average of 0.25 (g/m 3 )
compared with the earlier EC value of 2 (g/m 3 ). Box 5.3 shows trends in the maximum lead
content of petrol since 1977, the emissions of lead, and the clear relationship with the trend in
airborne lead concentrations.
As concern about lead from petrol declined, attention focused on other pollutants. The major
gaseous emissions from road vehicles, carbon monoxide, volatile hydrocarbons and oxides of
nitrogen are all environmentally damaging in some way. Carbon monoxide is rapidly taken up
by the hæmoglobin in the blood, and reduces its oxygen carrying capacity. It can be fatal at high
concentrations. Some hydrocarbons such as benzene and 1,3–butadiene are recognised
carcinogens, and nitrogen dioxide damages the respiratory system. Moreover, reactions in the
atmosphere involving hydrocarbons and oxides of nitrogen lead to the formation of ozone,
another respiratory irritant, and acidic compounds.
Airborne
lead
concentrations
have
fallen in step with
emissions of lead from
petrol vehicles. Although
the maximum permitted
lead content of petrol has
been unchanged since
1987, emissions and
concentrations
have
continued to reduce as
the use of unleaded petrol
has increased.

Box 5.3: Changes in lead emissions and concentrations since 1977 (adapted from
Hickman, 1989).
106

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

So, in much the same way as measures were taken to reduce lead pollution, controls were also
brought in to reduce other exhaust compounds. In this case, the legislation was introduced at
the European Community level through a series of emission control Directives and amendments
to them. The first was published in 1970 and concerned emissions of carbon monoxide and
hydrocarbons from petrol cars. The technical details of the Directive were adopted from the
Economic Commission for Europe (ECE) Regulation 15, and the early standards are often
referred to in that way. A sequence of four amendments were made to the legislation in the
1970s and 80s. The amendments introduced improvements to the test procedure, extended the
Directives coverage to include diesel as well as petrol cars, included oxides of nitrogen in the
pollutants that were controlled and, above all, reduced allowable emissions.
None of this series of standards, however, necessitated a fundamental change to the emission
control systems used on the cars, but this changed when an EC Directive was published in 1991
that dramatically reduced maximum allowable emission rates. Following its implementation in
1993, it was necessary for petrol cars to use closed loop, three way catalysts in order to achieve
the required emission standards (see Box 5.4). Subsequently, further reductions have been
required for cars registered in 1996 and 2000, and they will continue to be made more stringent
in further stages.

Air

Exhaust

1

5

2

Fuel

4

3

Air and fuel enter the
engine
(2)
via
the
metering device (1). For
the catalyst to operate
well,
the
exhaust
composition must be
controlled, using the
sensor (4). Deviations
from
the
correct
composition are corrected
by the engine control unit
(3). The catalyst (5) will
oxidise carbon monoxide
and hydrocarbons to
carbon dioxide and water,
while reducing oxides of
nitrogen to nitrogen.

Box 5.4: Schematic representation of a closed loop three way catalyst (from Bosch, 1993).
Although they were first introduced at a later date, an analogous set of regulations also control
emissions from the engines used in heavy duty vehicles. The regulations for both light and
heavy duty vehicles require that an example be tested and certified to comply with the
necessary emission limits before the model may be marketed in the EU.
The success of these standards may be seen in the results of emission tests carried out on
engines and vehicles manufactured at different times and under different regulations. Broadly,
the rates of emission from the most modern vehicles are lower by an order of magnitude when
compared with those of the 1970s. A few examples are given in Box 5.5.

5.2.2 Current air quality
Reducing vehicle emissions will reduce the concentrations of air pollutants, but the changes
will not always be in direct proportion. It has been seen that changes in lead emissions correlate

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

107

Changes to EU emission
regulations for cars have
been made periodically
since they were introduced
in 1970. Their cumulative
effect has been to reduce
permissible
levels
of
exhaust emission by about
90% for the gaseous
pollutants, CO, HC and
NO X .

The effect of the legislative
changes on emissions from
cars in use can be seen
from measurements made
by remote sensing. The
remote sensing system can
take readings from cars as
they drive through a
detector beam, allowing
many
hundreds
of
measurements to be taken
in a relatively short time.
When the results are
averaged by year of
registration, the large
improvements in emissions
become obvious.
Changes in standards have
also
given
significant
reductions in emissions
from heavy duty vehicles.
Diesels emit low levels of
CO, and relatively low
levels of HC, so most
emphasis has been given to
NOX and PM. The Euro 4
standards are scheduled for
introduction around 2005.
By that time emissions are
anticipated to be around
15% of those before
regulation.

Box 5.5: Changes in standards and emissions from road vehicles.
very well with changes in airborne lead concentrations (Box 5.3). This is because
nearly all of the lead in air is from petrol vehicle exhaust, and the compounds are
reasonably stable in the atmosphere. The same is also true, and for the same
reasons, for carbon monoxide, but for other pollutants these conditions are not
necessarily fulfilled. Oxides of nitrogen, for example comprise a mixture of nitric
108

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

oxide and nitrogen dioxide, and the proportions of each vary depending on their concentration
and their equilibrium with oxidising agents (mainly ozone) in the air. Where there is an excess
of ozone, it will react with nitric oxide to produce nitrogen dioxide, but when it has been
depleted by the reaction, no more nitrogen dioxide will be created even if more nitric oxide is
emitted. Fine atmospheric particles arise from many natural sources and human activities, so a
change in road vehicle emissions will only affect a relatively small part of the total
concentration.
Consequently, although significant gains have been made in the control of pollutant emissions
from all types of road vehicle, it is not yet possible to conclude that all air pollution problems
have been resolved. Thus, the 1995 Environment Act introduced a nationwide system for local
air quality management in which local authorities are required to review and assess air quality
in their areas and to develop a remedial action plan where air quality objectives are not

Pollutant

Objective
Concentration

Benzene
1,3–butadiene
Carbon monoxide
Lead
Nitrogen dioxide

Ozone

Particles (PM 10 )

Sulphur
dioxide

Date to be
achieved by
Measured as

16.25 µ/m 3 (5 ppb)
running annual mean
3
2.25 µ/m (1 ppb)
running annual mean
11.6 µ/m 3 (10 ppm)
running 8 hour mean
3
0.5 µ/m
annual mean
0.25 µ/m 3
annual mean
200 µ/m3 (105 ppb)
1 hour mean
not to be exceeded
more than 18 times
a year
annual mean
3
40 µ/m (21 ppb)
100 µ/m 3 (50 ppb)
daily maximum of running
not to be exceeded
8 hour mean
more than 10 times a year
50 µg/m 3 not to be exceeded
more than 35 times a year
40 µ/m 3
350 µg/m 3 (132 ppb)
not to be exceeded
more than 24 times a year
125 µg/m 3 (47 ppb)
not to be exceeded
more than 3 times a year
266 µg/m 3 (100 ppb)
not to be exceeded
more than 35 times a year

31
31
31
31
31
31

December
December
December
December
December
December

2003
2003
2003
2004
2008
2005

31 December 2005
31 December 2005

24 hour mean

31 December 2004

annual mean
1 hour mean

31 December 2004
31 December 2004

24 hour mean

31 December 2004

15 minute mean

31 December 2005

Box 5.6: Objectives of the National Air Quality Strategy.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

109

Exceedences of the NO 2 standard are seen at many sites. Indeed, the only sites with levels well below the AQS
objective are at remote and rural locations. The highest concentrations are at roadside and kerbside locations, though
similar levels are found at urban background and centre sites.

Box 5.7: Air pollution concentrations in the UK, 1996. 5.7a: Nitrogen dioxide.

The standard for ozone is exceeded at all of the sites where it was measured. There is little difference between
concentrations recorded at rural and remote locations and those at urban sites. Only one of the sites is at the roadside,
and the concentration there is one of the lowest shown.

Box 5.7: Air pollution concentrations in the UK, 1996. 5.7b: Ozone.

110

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

achieved. The Act also required the preparation of a National Air Quality Strategy (NAQS) to set
out in detail the objectives to be achieved. This was published in March 1997 (Department of
the Environment et al ). The Strategy identifies eight priority pollutants and, for each of them, it
provides an air quality standard and objective, defined as:
“Standards are the concentrations of pollutants in the atmosphere which can broadly be taken
to achieve a certain level of environmental quality. The standards relating to the quality of air
are based on the assessment of the effects of each pollutant on public health.”

“The objectives provide policy targets by outlining what the Government intends should be
achieved in the light of the air quality standards.”
Following a review of the Strategy, revised objectives were defined and published in January 2000
(Department of the Environment, Transport and the Regions et al). They are listed in Box 5.6.
With reference to these objectives, an overview of the current situation in the UK can be
obtained from the extensive network of pollution monitoring stations operated on behalf of the
Department of the Environment, Transport and the Regions. In Box 5.7, graphs are shown
displaying the concentrations of these priority pollutants measured in 1996 (Broughton et al
1998). The concentrations are given in terms appropriate to the NAQS objective, and the
objective’s concentration value is shown as a horizontal line. In this way, the general frequency
of exceedences can be seen. The DETR network has sites in a wide variety of locations, from
remote sites such Strath Vaich in the Scottish Highlands to busy kerbside locations such as the
Cromwell Road in West London, and encompassing suburban, urban background, central urban
and industrial sites. The sites are ordered, from the most remote at the left to kerbside at the
right of each graph. Thus, the position of each bar gives an approximate indication of the traffic
influence at each site.

All carbon monoxide sites are in urban areas, so none of the results shows the very low values that would be expected at a
rural location. Only one exceedence occurs, at the roadside site, and the amount by which the standard is exceeded is small
(10.2 ppm, with a standard of 10 ppm).

Box 5.7: Air pollution concentrations in the UK, 1996. 5.7c: Carbon monoxide.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

111

A wide range of results is shown for sulphur dioxide. The highest level was actually measured in Belfast, where there is
still much use of coal for domestic heating (coal has a high sulphur content). Levels at roadside locations show little
difference from those elsewhere: the second lowest is at roadside site, while that at another roadside site is among the
highest.

Box 5.7: Air pollution concentrations in the UK, 1996. 5.7d: Sulphur dioxide.

The PM 10 standard is exceeded at all but two sites. Although all of the sites are suburban or urban, there seems to be
little difference between levels at different types of location. 1

Box 5.7: Air pollution concentrations in the UK, 1996. 5.7e: PM 10.
1 The data and observations on PM concentrations were made with reference to the NAQS of 1997. The 2000 revision makes the
10

objective somewhat less stringent, so the likelihood of exceedences is lower. Nevertheless, PM 10 is still regarded as one of the most
serious pollutants, and there appears not to be a level below which there are no health risks, so the general conclusion is not altered.

112

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

While measurements of benzene are made at relatively few locations, it is clear that concentrations are well below the
standard. The highest concentrations are at an urban centre location and at a roadside site in London. At the rural site
the concentration is lowest.

Box 5.7: Air pollution concentrations in the UK, 1996. 5.7f: Benzene.

The pattern of 1,3–butadiene concentrations is identical to that for benzene, though concentrations are about 5 times
lower. All are well below the standard of 1 ppb.

Box 5.7: Air pollution concentrations in the UK, 1996. 5.7g: 1, 3 Butadiene.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

113

The locations at which lead is monitored include a group of rural sites, several sites near to industrial sources, urban
centre sites and a group of roadside sites. The only sites at which the standard is exceeded are those associated with
industrial emissions. Those at the roadside sites are generally higher than the urban centre and rural concentrations,
but nevertheless well below the standard.

Box 5.7: Air pollution concentrations in the UK, 1996. 5.7h: Lead
On the basis of these observations, it is possible to draw the following conclusions on the
priorities of the various pollutants, the extent to which road traffic is involved and the necessity
or otherwise of supplementary controls:
❍ Ozone concentrations are higher than is desirable, and the reactions of vehicle emissions
contribute to the formation of ozone. On a very local level, however the main impact of
traffic is to reduce ozone concentrations by emitting nitric oxide with which it quickly
reacts. Ozone pollution is a regional phenomenon and is caused by pollution from many
sources in the UK and mainland Europe. The control options likely to be most successful
are those presently being pursued, that is the control of ozone precursors at their
emission source.
❍ Nitrogen dioxide concentrations in urban areas are high mainly because of the emissions
from road traffic. Reductions in oxides of nitrogen emissions, may have little effect on
roadside concentrations because there is usually an excess of nitric oxide so that the
formation of nitrogen dioxide is limited by the availability of oxidants. At urban
background locations, however, where the nitric oxide concentration is lower, it may
become the limiting factor and decreases in emissions would be beneficial.
❍ Carbon monoxide, benzene and 1,3–butadiene levels rarely exceed the health standards
and will reduce further in the future because of the introduction of cleaner vehicles into
the road transport fleet. It is probably unnecessary to implement any additional controls.
❍ Sulphur dioxide levels are usually below the standard, and where they exceed it there is
often a local, non–traffic related source of emissions. Given current levels of sulphur in
road fuels, road transport produces only a very small fraction of sulphur dioxide
emissions. Standards for future fuels specify even lower levels of sulphur and additional
controls on transport emissions are not needed.
114

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

❍ It is estimated that road transport accounts for less than a third of PM 10 emissions
nationally. However, the proportion is likely to be higher in urban areas and near to
roads. Because this pollutant is probably the cause of greatest concern and
concentrations often exceed the standard, additional reductions in emissions, including
those from road vehicles, are desirable.
❍ Only where there are industrial sources of lead are concentrations in excess of the
standard. The phasing out of lead in petrol in 2000 means that traffic emissions will
virtually disappear (they may continue at a very low level because of traces of lead in
unleaded petrol and the limited exceptions to the ban on lead additives such as a few
classic and vintage cars). No further actions are needed.
In summary, further reductions of emissions of oxides of nitrogen and PM 10 would be beneficial,
and it is those pollutants that environmental management policies should address. Emission
control through better engineering, promoted by increasingly stringent vehicle emission
standards, has been successful in bringing down levels of other traffic–related compounds so
that they are almost always below the standards.
Most attention so far has been given to the emission and propagation of pollutants that may
damage health. There are, however, other types of impact, including contributions to the
regional and global problems of acid deposition and the greenhouse effect. Regarding the first
of these, the pollutants already discussed, especially hydrocarbons and oxides of nitrogen, are
especially implicated, but a different pollutant, carbon dioxide is the most important of the
greenhouse gases.
Carbon dioxide is formed when any carbon containing material is burnt. This includes almost all
of the fuels used, including petrol and diesel (and the other fuels that have been used or proposed
as suitable for road transport with the exception of hydrogen and electricity if it is generated by
a non–combustion plant). While there have been very significant reductions in the emission of
most pollutants by road vehicles, reductions in carbon dioxide emissions have been much more
modest. Because it is the natural end product of the combustion process, the amount of carbon
dioxide is proportional to the amount of fuel used, and that in turn is proportional to the amount
of transport activity provided. The only ways to reduce carbon dioxide emissions is to reduce the
amount of transport or to increase its efficiency: neither of these has happened systematically in
the past (Box 5.8). It is therefore also important that environmental management policies and
actions should seek to restrict fuel consumption and carbon dioxide emissions.

5.3 Current practice for impact assessment
The way in which priorities have changed in response to increasing information on their effects
and on the relative success of control policies and technologies for the different pollutants has
been paralleled by developments of the procedures to assess the air pollution impacts of roads.
The Manual of Environmental Appraisal was superseded in 1993 by Volume 11 of the Design
Manual for Roads and Bridges (DMRB) (Department of Transport et al ).
The first version of this Volume of the DMRB was produced partly in response to the EU
Directive 85/337/EEC on environmental impact assessment. The Directive required that an
assessment of environmental impacts be carried out before consent could be given for certain
development projects such as large scale industrial or infrastructural developments. The effects
on the following four sectors must be identified, described and assessed:
❍
❍
❍
❍

human beings, fauna and flora;
soil, water, air, climate and the landscape;
the interaction between the first two groups, and
material assets and the cultural heritage.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

115

Freight transport by road has increased substantially measured in both tonne.km and vehicle.km. In the
same period, the tonnage of freight transported has increased by about 25%, and the larger increase in
tonne.km shows that goods are being carried over longer distances. Thus, the fuel consumed per tonne
of freight delivered has increased.

Box 5.8a: Trends in transport activity and carbon dioxide emissions.

Passenger transport has also increased. Car fuel consumption improved considerably after concerns
about oil supplies in the 1970s, but since then it has remained fairly constant.

Box 5.8b: Trends in transport activity and carbon dioxide emissions.

116

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

While carbon dioxide emissions in most sectors have been falling, those from road transport have more than doubled
since 1970.

Box 5.8c: Trends in transport activity and carbon dioxide emissions.

In order that UK practice could conform more closely with the Directive, a new part was
introduced into the DMRB which provided a method of calculating the change in total
emissions of pollutants that would result from a road scheme. At the same time, the opportunity
was taken to extend the range of pollutants that were evaluated. There have subsequently been
two revisions to the DMRB. The latest version has been designed to be compatible with the
National Air Quality Strategy in terms of the pollutants that it considers and the air quality
standards to which it refers. Thus, air pollution estimates are made for the local impacts of
carbon monoxide, nitrogen dioxide, benzene, 1,3–butadiene and PM 10 , and for assessing the
potential regional and global impacts, estimates are made of the emissions of carbon monoxide,
oxides of nitrogen, total hydrocarbons, particulates and carbon dioxide.

5.4 Issues
The air pollution impact of road traffic can be described as a sequence of interacting stages.
First is the need for a particular transport operation and the decision on how it should be carried
out. Then the operation takes place, and its exact nature influences the amount of pollution
emitted. The emissions are dispersed, diluted and chemically transformed in the atmosphere,
and during that time they may impact on one or many parts of the environment. These stages
may also be taken to indicate areas in which it may be possible to introduce control policies
and practices. Transport planning may be used to optimise freight and passenger transport;
driving behaviour and vehicle technologies can be modified to produce less polluting journeys,
and land use practices could be helpful in segregating the transport activity from the most
sensitive parts of the environment.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

117

Consequently, the share of carbon dioxide emissions from road transport has increased from less
than 10% of the national total to more than 20%.

Box 5.8d: Trends in transport activity and carbon dioxide emissions.

In the following paragraphs, consideration will be given only to the ways in which transport by
road may be made less polluting. The broader issues of transport and land use policies may in
some circumstances be more effective, but they are outside the scope of this chapter.

5.4.1 Vehicle emissions
Vehicle emission rates depend on many factors which may be classified in two broad groups:
technical factors relating to the design and engineering of the vehicles and operational factors
relating to the way in which they are used.
Some of the technical aspects have already been mentioned in the discussion of emission
standards, as it is these that have been instrumental in promoting the cleaner technologies. In
most classification systems used in studies of road vehicle emissions, several technical
parameters are included to distinguish groups according to their emission characteristics.
Commonly, these include the type of engine (for example, spark ignition, compression ignition,
two–stroke), the fuel (petrol, diesel and perhaps alternative fuels such as compressed natural gas
or methanol), the size of the vehicle (as indicated, for example, by the engine capacity, the
weight or seating capacity) and the emission control standard (often using the vehicle’s age to
show the standard to which it was constructed, or sometimes by technology type such as
three–way catalyst or particulate trap). A few examples of differences in rates of emission
attributable to these technical features of the vehicles are presented in Box 5.9.
118

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Carbon monoxide emissions from cars are strongly influenced by the fuel – diesel produces much less than petrol.
Directive 91/441 saw the introduction of three–way catalysts, and a significant reduction in petrol car emissions.

Box 5.9: Examples of the effects of vehicle technical features on rates of exhaust emission.
5.9a: Fuel.

Particulate emissions also depend on the fuel and the vehicle type. In this case, diesels are the highest emitters, and
the size of the vehicle is also influential: LGVs emit more than cars; buses and HGVs more than LGVs.

Box 5.9: Examples of the effects of vehicle technical features on rates of exhaust emission.
5.9b: Vehicle type.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

119

The weight of a goods vehicle obviously influences its carbon dioxide emissions since they are proportional to the fuel
consumption. It also has a marked effect on emissions of oxides of nitrogen.

Box 5.9: Examples of the effects of vehicle technical features on rates of exhaust emission.
5.9c: Weight class.
While these technical aspects are extremely important determinants of a vehicle’s emissions
performance, they are perhaps less directly the concern of those responsible for highway
management than the operational features that are discussed below. However, there are ways in
which roads may be regulated in order to control the composition of the traffic, and the criteria
could be based on the known emission characteristics of the vehicles. A number of local
authorities are, for example, considering the designation of low emission zones into which
vehicles will only be permitted if they reach the necessary standard of emission control (see, for
example, Cloke et al 2000; Hitchcock et al 1999). Restrictions could be based on vehicle age,
which dictates its emission standard to a large extent, or perhaps use a permit system where it
is necessary to gain prior permission to enter the zone. Other possible examples can be seen in
policies that have already been used for other purposes, such as lorry weight restrictions in
some urban areas, night–time lorry bans and dedicated vehicle lanes (for example, bus, high
occupancy vehicles).
A single vehicle of a particular type will display wide variation in emissions depending on the
way it is used: many aspects of operation can be shown to affect a vehicle’s emissions. The
variable most often used to indicate a vehicle’s operating condition in emission studies is its
average speed during a trip. Many compilations of road vehicle emission factors provide
expressions for rates of emission as functions of average speed, and these functions are well
characterised (Box 5.10). Highest emissions are found at low speeds, which typically involve
frequent stops and starts, accelerations and decelerations. Operations of this type are inefficient
because the energy supplied to bring the vehicle to a certain speed is subsequently wasted when
it brakes to slow down or stop. There is also a tendency for some increase in emissions at high
speeds when extra fuel has to be delivered to provide the necessary high power.
120

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Thus, while rates of emission are often expressed relative to a vehicle’s average speed, the speed
itself is not the direct cause of the variation. Rather, it is the sequence of operation of the engine
in order to produce a particular speed pattern. Implicit in the use of the average speed is the
assumption that certain road and traffic conditions will engender typical and repeatable
behaviour, giving rise to similarities in both the average speed and the more detailed operation
of the vehicles. However, recognising that the average speed is only a generalised indicator of
vehicle operations has promoted emission studies in which other variables have been used.
Most commonly, these are the vehicle speed and acceleration for light duty vehicles, and the
engine speed and load for heavy duty vehicles, chosen as parameters more directly related to
the operation of the engine and vehicle and thus potentially capable of explaining their
emissions performance more accurately (Box 5.10).
As well as these basic relationships between the motion of the vehicle and its engine’s
performance, other aspects of its operating environment are important. The load carried by a
vehicle affects its total weight, its fuel consumption and emissions. This is especially important
for heavy goods vehicles where the payload represents a much higher proportion of its total
weight than for other types of vehicle. Fuel consumption, oxides of nitrogen emissions and
particulate emissions from heavy duty diesels all show a relatively linear increase with the
weight of a vehicle. For an increase from 25 to 35 tonnes, oxides of nitrogen emissions increase
by about 50%, and those of particulates by about 15%. That is not to say, however, that it is
beneficial to operate vehicles with a lower payload, because then more trips would be
necessary to transport the same amount of goods. In a similar way, the additional energy needed
to climb road gradients also increases fuel consumption and emissions.
For a more comprehensive discussion of these issues, see Hickman (1999), from which many of
the examples are taken.

Carbon monoxide emissions from light duty vehicles show the characteristic increase at low speed, because of
inefficient stop–start driving, and at high speed, because of the increased power demand.

Box 5.10a: Typical variations in vehicle emission rates according to their operating conditions.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

121

Oxides of nitrogen from heavy duty vehicles show a rather similar trend, although the increase at high speed is less
pronounced.

Box 5.10b: Typical variations in vehicle emission rates according to their operating conditions.

Oxides of nitrogen emissions from catalyst equipped petrol cars show a systematic increase with instantaneous speed
and with speed x acceleration (the product is used rather than acceleration alone because it is a better indication of the
power output from the engine).

Box 5.10c: Typical variations in vehicle emission rates according to their operating conditions.

122

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

When an engine is cold, the fuel does not evaporate fully when it is introduced into the engine.
This means that more fuel must be supplied in order to provide a mixture that will burn
smoothly. The use of fuel enrichment systems for cold engines causes emissions of carbon
monoxide and hydrocarbons to increase substantially, as well as the fuel consumption. This
effect is especially noticeable for petrol engined vehicles. The use of catalysts on these vehicles
compounds this “cold–start” effect, as catalysts need an accurately controlled exhaust
composition for good efficiency, and also need to reach a temperature in excess of 300°C before
they become effective. Under cold start conditions, neither of these conditions is met and rates
of emission may be an order of magnitude higher than from a hot engine and catalyst (although
they are no higher, in absolute terms than those from a non–catalyst vehicle). The temperature
dependency of emissions means that other aspects of vehicle operation influence them. The
number of trips a vehicle makes and the duration of the intervals between trips clearly dictate
the number of times it is started from cold, and each of those cold starts will result in excess
emissions being created. These operational features are also important in terms of emissions of
hydrocarbons by evaporation of the fuel.

5.4.2 Atmospheric dispersion and transformation
In general, the processes and conditions that control the dispersion and reactions of the
emissions in the atmosphere are outside the control of those responsible for highway
management. Largely, they are the result of natural physical and chemical interactions
influenced primarily by meteorological conditions. Nevertheless, it is important to understand
the basic principles of these processes in order to be able to consider the likely outcome of any
action in terms of its effects on air pollution concentrations.

Concentrations of total oxides of nitrogen measured near to the M4 motorway clearly reduce as the wind speed
increases. The relationship shows considerable scatter as the concentrations are also influenced by other conditions.

Box 5.11a: Observations of the influence of wind speed and direction on the dispersion of
traffic pollution.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

123

Concentrations are highest when the wind direction is between south and west. Winds in this sector blow over the M4
towards the monitoring site. Winds in the opposite direction blow cleaner air to the monitoring site as it has not been
polluted by traffic emissions.

Box 5.11b: Observations of the influence of wind speed and direction on the dispersion of
traffic pollution.
Perhaps the most important influence on the spread of the pollution after its release is the
strength of the wind. Clearly, the emissions will be dispersed more quickly, and pollution
concentrations will be lower on a windy day than on a still day. The destination of the pollution
cloud depends principally on the direction of the wind (Box 5.11).
For an inert gas, the average effect of this wind–influenced dispersion is that the pollution
concentration decreases with distance from the road. As a rule of thumb, the concentration
halves for every 25–30m from the road and reaches a level not much above the background
after 150–200m. In urban areas, patterns of windflow are complex, and the situation is not so
simple as that at the rural motorway location chosen for this example, but the principles remain
the same. The pollutant emissions are diluted and dispersed by the movement of the air, and
concentrations tend to reduce with increasing distance from the traffic.
The second important factor, for some compounds is their reactivity in the atmosphere. Many of
the reactions that take place are photochemical (that is, are promoted by the absorption of solar
radiation), which has given rise to the term photochemical smog to describe the mixture of
gases and aerosols that result from the reactions. The mechanisms of the interactions are
extremely complex, but their products include ozone, peroxyacetyl nitrate and other oxidants,
aldehydes and ketones, acids and secondary particulates, predominantly nitrates and sulphates.
The full range of reactions and products are significant with regard to environmental impacts
over medium to long distances, but in the context of pollution concentrations near to roads,
perhaps the most important relationship is that between nitric oxide, nitrogen dioxide and
ozone. A large majority of the oxides of nitrogen emitted by road vehicles is in the form of nitric
oxide, which reacts rapidly with ozone in the air to produce nitrogen dioxide. Because nitrogen
124

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Carbon monoxide is inert and has a low background level, so the concentration falls normally with increasing distance
from the road. Nitrogen dioxide is being produced by chemical reactions at the same time as it is diluted by the wind.
The combined effect is a slower rate of fall in concentration. PM 10 has a high background level, so although the traffic
emissions disperse in the normal way, the concentration does not fall to a very low value.

Box 5.12: Concentration profiles for a variety of air pollutants.
dioxide has a much greater potential to damage health than nitric oxide, it is the net result of
the emission and its reaction that is of importance. In many cases the formation of nitrogen
dioxide is limited by the availability of ozone for the reaction rather than nitric oxide.
Finally, it should be noted that there is a background level of each of the pollutants under
discussion, and that locally produced pollution from traffic emissions is superimposed on this
pre–existing concentration. This arises in part from natural processes (for example, sea salt
particles are found in the air even at inland locations), and in part from the spread of pollution
created by human activities. The significance of the background pollution varies substantially
for the different pollutants. Carbon monoxide, as one example, is nearly all from road vehicle
emissions, and the background concentration tends to be rather small. For PM 10 , though, there
are a multitude of sources in addition to the traffic so that, on average, two thirds of what is
measured in urban air may be considered to be background material.
Because of the variations between pollutants, their concentration profiles in the vicinity of a
road show rather different shapes. Box 5.12 illustrates this for carbon monoxide, nitrogen
dioxide and PM 10 .

5.5 Legislation and responsibilities
Reference has been made in previous sections to a number of regulations and standards relevant
to the control of air pollution from traffic. Broadly, these fall into three classes: standards for the
emissions performance of vehicles and fuels, standards for local air quality and international
agreements and protocols concerning national emissions of pollutants.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

125

Document reference
LAQM.G1
LAQM.G2
LAQM.G3
LAQM.G4
LAQM.TG1
LAQM.TG2
LAQM.TG3
LAQM.TG4

Subject
Framework for review and assessment of air quality
Developing local air quality action plans and strategies
Air quality and transport
Air quality and land use planning
Monitoring for air quality reviews and assessments
Preparation and use of atmospheric emission inventories
Selection and use of dispersion models
Pollutant specific guidance

Box 5.13: Guidance documents issued for assistance with local air quality management.
5.5.1 Vehicle and fuel standards
Road vehicles sold in the UK must be type approved for emissions in accordance with
appropriate EU Directives. For light duty vehicles (up to 3.5 tonnes gross weight), an example
of each model is driven on a rolling road over a predetermined driving cycle and under strictly
controlled conditions. Emissions are collected and analysed for carbon monoxide, total
hydrocarbons, oxides of nitrogen and, for diesel vehicles, total particulates. The emission rates
must be below defined limit values for the model to be approved.
For heavy duty vehicles a slightly different procedure is used, in that only the engine is tested, on
an engine dynamometer. Nevertheless, the same principles apply: the engine is operated over a
defined duty cycle and rates of emission must be below set limits for approval to be given.
Very large reductions have been made to the allowable rates of emission, and modern vehicles
are substantially less polluting than their predecessors (see Box 5.5).
This type approval test applies to new engines and vehicles. It is the responsibility of the
manufacturer to ensure that the standards are achieved through good design, engineering and
manufacturing procedures. However, once a vehicle has been sold, it becomes the
responsibility of its operator to ensure that a good standard is maintained. UK and EU
regulations require periodic inspections to be made of each vehicle’s emissions performance:
for cars in the UK, this is done as part of the “MOT” test, and for HGVs during their analogous
annual inspection. Carbon monoxide and hydrocarbon emissions from petrol vehicles and
smoke emissions from diesel vehicles must be below the relevant limit values for a pass
certificate to be awarded. As a supplement to the periodic inspection, the Vehicle Inspectorate
operates random roadside tests 2 .
Good quality fuels are necessary to allow vehicles to operate to their full potential, and fuel
qualities are also regulated through British Standards and EU Directives. Many of the fuel
properties covered by the standards have an influence on emissions, and a number of recent
studies have examined these links. Largely as a result of the Auto Oil Programmes in Europe
(tri–partite research programmes involving the European Commission, vehicle manufacturers
and the oil industry, see also Section 2.3.3), the latest fuel standards have been developed with
emission control as one of their main objectives. The purpose of the most recent EU Directive
(98/70/EC) is:

“To set a range of technical specifications, on health and environmental grounds, for petrol and
diesel fuels. As well as providing emissions benefits in their own right, these tighter
specifications are necessary to enable the use of advanced technology for emissions control and
greater fuel efficiency.”
2 In 1998 and 1999, a number of local authorities piloted a scheme of random roadside checks. Owners of vehicles
found to fail the emission test could be subject to a fixed penalty fine of £60. No decision has yet been taken on the
extension of this pilot experiment.

126

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Pollutant
Benzene

Measurement techniques
Benzene is usually measured by gas chromatography (GC). Samples can be collected by
drawing air through a suitable adsorbant and are then desorbed and introduced into a GC for
analysis. The desorption can be by a solvent or by heating. Instruments are also available that
will perform the analysis almost continuously. These are GCs fitted with a gas sampling
system which take and analyse samples automatically, several times an hour.

1,3–butadiene

1,3–butadiene measurement methods are very similar to those for benzene. Different
adsorption and desorption procedures and different chromatographic conditions are needed,
but the same principles apply.

Carbon monoxide

Measurement of carbon monoxide is most often based on its absorption of infra red radiation
at a certain wavelength. Instruments sample the air continuously and the concentration is
determined from the difference in absorption between the sample and a reference. Another
method measures the current generated when an air sample is passed through a special
electrochemical cell in which carbon monoxide is oxidised to carbon dioxide.

Lead

Almost all of the lead emitted by road vehicles is in the form of fine particles of lead salts.
The concentration is usually found by the laboratory analysis of particles collected by
drawing air through a suitable filter. The lead is extracted using an acidic solvent. The
resulting solution can be analysed by many techniques, of which perhaps the most common
are atomic absorption spectrophotometry and inductively coupled plasma mass spectrometry.

Nitrogen dioxide

Continuous measurements of nitrogen dioxide are usually made using a chemiluminescence
analyser. The reaction between nitric oxide and ozone produces a chemiluminescence
proportional to the nitric oxide concentration. Instruments measure nitric oxide and total
oxides of nitrogen (following the reduction of nitrogen dioxide in the sample to nitric oxide),
and nitrogen dioxide is determined as the difference. Another commonly used method is the
nitrogen dioxide diffusion tube. These are passive devices that absorb nitrogen dioxide from
the air to which they are exposed by its reaction with triethanolamine that coats the tubes’
surface. The concentration is determined from the known absorption characteristics of the
tube, following the laboratory analysis of its contents. The tubes only provide an average
concentration for the period that they are exposed, typically a few days.

Ozone

Ozone is usually monitored through its absorption of ultra violet radiation at a particular
wavelength. Analysers continuously measure the concentration in the sample air, which is
directly proportional to the amount of absorbance.

Particles

There are many methods available for the measurement of particles. Basic mass
measurements are usually made by collecting particles on a filter – special air inlets can be
used to discriminate size fractions such as PM 10 or PM 2.5 . Continuous mass measurements
may be obtained using a tapered element oscillating microbalance, which determines the
changing weight of the filter by its effect on the oscillation frequency of a crystal upon which
it is mounted. When period averages are needed, the filters are weighed on an analytical
balance before and after the particles are collected. Particle size distributions, particle
number counts and other properties may be monitored with specialist equipment. Another
common method is the British Standard “black smoke” determination. Particles are collected
on a filter and their concentration is estimated from the darkness of the stain they produce.

Sulphur dioxide

Sulphur dioxide has been monitored in the UK for many years. Traditionally, the method has
been to absorb sulphur dioxide by passing air through a solution of hydrogen peroxide and
to determine the resulting sulphuric acid by titration with sodium borate solution. More
recently, though, a number of continuous, instrumental techniques have been made
available. The most common are based on flame photometry or pulsed fluorescence. In a
flame photometer, the sulphur dioxide is burnt in a hydrogen flame and emits ultra violet
radiation proportional to its concentration. The pulsed fluorescence method uses ultra violet
radiation to excite the molecules of sulphur dioxide, and the resulting fluorescence is
proportional to the concentration.

Box 5.14:
Common
techniques for
measuring air
pollutants.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

127

A laboratory for measuring air
pollution situated at the M25
motorway
near
to
Staines,
Middlesex, operated on behalf of the
Highways Agency. The equipment
that can be seen on the roof of the
building includes a size specific inlet
for sampling airborne particles and
instruments
to
measure
meteorological conditions.

A mobile air pollution monitoring
laboratory in position near to the M4
motorway in Berkshire.

An interior view of the mobile
laboratory. The instruments are
commercially available analysers for
a variety of air pollutants, together
with supporting equipment to service
and calibrate the analysers and to log
the data they measure.

Box 5.15: Fixed and mobile air
pollution monitoring stations.

128

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

5.5.2 Air quality standards
The UK National Air Quality Strategy (now the Air Quality Strategy for England, Scotland, Wales
and Northern Ireland) has already been introduced in Section 5.2.2, where it has been seen that
quantitative air quality targets have been set, and should be achieved between 2003 and 2008.
The latest objectives of the Strategy, published in January 2000, draw heavily on the air quality
legislation recently adopted by the EU. Air quality standards for certain pollutants have existed
in EU legislation for many years, but in 1996, a more coherent approach was adopted with the
publication of the Air Quality Framework Directive . This established a framework under which
limits would be set for twelve pollutants: sulphur dioxide, nitrogen dioxide, particulate matter,
lead, carbon monoxide, benzene, ozone, polycyclic aromatic hydrocarbons, cadmium, arsenic,
nickel and mercury. The limits themselves would be established in a series of pollutant–specific
“Daughter Directives”.
The first of these was adopted in 1999 and establishes legally binding limit values for sulphur
dioxide, nitrogen dioxide, particles and lead to be achieved by 2005 and 2010. Subsequently,
proposals have been made for further directives, one to set limit values for benzene and carbon
monoxide, a second to set target values for ozone, and a third setting national emissions ceilings
for sulphur dioxide, nitrogen dioxide, ammonia and volatile organic compounds, to be achieved
by 2010.

5.5.3 International agreements
There are a number of international protocols under which many countries, including the UK,
have agreed on targets for reductions in emissions. The achievement of the targets will be
through a combination of controls on many emission sources, including road transport.
The United Nations Economic Commission for Europe (UNECE) Convention on Long Range
Transboundary Air Pollution entered into force in 1983, and lays down general principles for
international cooperation on the abatement of air pollution. It has been followed by a series of
protocols giving more specific commitments. The Helsinki Protocol (1985) called for a
reduction of SO 2 emissions by 30%, based on 1980 levels, to be achieved by 1993, and the
Sofia Protocol (1988) required that NO X emissions should return to 1987 levels by 1994. The
UK met both of those targets, although it was not formally a party to the Helsinki Protocol.
Two further current protocols under this Convention have also been ratified by the UK. The
Protocol Concerning Emissions of VOCs or their Transboundary Fluxes (1991) commits parties
to a reduction in emissions of 30%, based on 1988 levels, by 1999. The Second Protocol on the
Further Reduction of Sulphur Emissions (1994) requires the UK to reduce emissions by 80%,
based on 1980 levels, by 2010.
In 1997, the Kyoto Protocol was adopted by parties to the United Nations Framework
Convention on Climate Change. Under this agreement, the EU has a legally binding target to
reduce emissions of greenhouse gases by eight percent below 1990 levels over the
“commitment period” of 2008 to 2012. The target will be shared between Member States, and
the UK’s contribution will be a reduction of 12.5%. This target was subsequently ratified and
strengthened at a meeting of ministers in Buenos Aires in 1998.

5.5.4 Local air quality management
The previous sections have detailed national and international standards applied for the control
of air pollution in the UK. However, in the 1995 Environment Act, the Government established
the basis for a system of local air quality management, devolving some powers and
responsibilities to local, rather than national government. Having established air quality
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

129

objectives, an assessment was made of the extent to which national and international policies
alone would be sufficient for their achievement. For some pollutants in some circumstances it
was recognised that supplementary local actions would be necessary. A staged approach was
therefore developed, under the local air quality management system, that would identify
problems and set out action plans for their resolution.
Local air quality management requires local authorities periodically to review and assess the current
and future air quality in their areas. If it is likely that the objectives of the Air Quality Strategy will
not be met, the authority must designate an “air quality management area” and produce an action
plan setting out the measures that it intends to take in order to mitigate the problem.
To support the local authorities in fulfilling these responsibilities, the Government has issued an
extensive series of guidance documents. It is not possible here to repeat their contents
extensively, but simply to list the topics they address (Box 5.13). More detailed information can
be found in the documents themselves (Department of the Environment, Transport and the
Regions, 2000).
In their discussion of local air quality management, the Government states:

“Because of various local factors, some poor air quality hotspots are likely to remain, even after
implementation of national policies and industrial regulation. These are often associated with
traffic, which is not controlled by any regulatory regime. The Government and the devolved
authorities believe these hotspots are best dealt with locally through local air quality
management.”
Much of the remainder of this chapter will examine this subject. It will consider the means
available to review and assess traffic pollution in a particular location through monitoring and
modelling and, for those situations where problems may be identified, consideration will be
given to the measures that can be used for control and mitigation on a local scale.

5.6 Review and assessment of air pollution
The approach to review and assessment recommended in the Air Quality Strategy involves three
stages:
❍ All authorities must undertake the first stage, which involves an initial screening of
pollution sources, particularly transport and industrial sources. The purpose is to identify
pollutants (if any) where there is a risk of exceeding the objectives. For road transport
sources, guidance is given as to the type of situation where this may be the case. For
example, for carbon monoxide, the type of road (single, dual carriageway or motorway)
and the flow of traffic may be used.
❍ The second stage should be carried out if the first stage has suggested that there is a
possibility that one or more of the objectives will be exceeded. It uses relatively simple
methodologies and is intended as a supplementary screening exercise to focus on
locations where the maximum impact is likely.
❍ If the second stage confirms the possibility that an air quality objective may be exceeded,
a third stage review is necessary. For the third stage, the authority is expected to
undertake a detailed and accurate appraisal of the potential impacts.
This procedure has much in common with the earlier approaches adopted in the Manual of
Environmental Appraisal and its successor, the Design Manual for Roads and Bridges . In each
case, the air pollution impact of a road network is assessed in stages depending on the
130

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

A selection of pollution sampling
devices. Some are passive samplers
which selectively adsorb certain
compounds from the air to which they
are exposed. Others have air pumped
through them and again adsorb specific
compounds. The contents are analysed
in a laboratory after sampling.

More sampling devices, including
filters and filter holders for taking
particle samples, a bubbler through
which air is passed to trap pollutants in
solution
and
a
system
that
automatically samples onto adsorption
tubes in sequence.

A long–path pollution monitoring
instrument operated by Wesminster
City Council. Radiation from the source
is reflected back to the detector. The
absorption in different wavelengths is
proportional to the concentration of
certain compounds encountered along
the radiation beam.

Box 5.16: A range of air pollution
monitoring equipment.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

131

The main sources of emission from road vehicles are the exhaust gases and hydrocarbons
produced by evaporation of the fuel. When an engine is started below its normal operating
temperature, it uses fuel inefficiently, and the amount of pollution produced is higher than
when it is hot. These observations lead to the first basic relationship used in the calculation
method, that is:

E+E hot+E start+ E evaporative

where:
E
E hot
E start
E evaporative

is
is
is
is

the
the
the
the

total emission
emission produced when the engine is hot
emission when the engine is cold
emission by evaporation (only for hydrocarbons)

Each of these contributions to the total emission depends on an emission factor and one or
more parameters relating to the operation of the vehicle, so that in general:
where:
Ex
ex
a

E x= e x

x

a

is one of the contributions to total emissions
is an activity related emission factor
is the amount of traffic activity relevant to this type of emission

The parameters e x and a are themselves functions of other variables.
For hot emissions, the activity related emission factor, e hot , is expressed primarily as a
function of the average speed of the vehicle. Modification factors (which may themselves be
functions of other variables) allow corrections to be made for features such as the road
gradient or the load carried by a vehicle. The activity, a, is then the amount of operation
(vehicle.kilometres) carried at a particular average speed, on roads with a certain gradient,
for vehicles with a certain load.
Start emissions, because they only occur during the early part of a journey, are expressed as
an amount produced per trip, and not over the total distance travelled. The emission factor,
e start , is calculated as a function of the average vehicle speed, the engine temperature, the
length of the trip and the length of the cold part of the trip. The activity, a , is the number of
trips. This procedure is used only for light duty vehicles. Because data for other types is very
limited, such detail cannot be used, and cold start emissions are proposed simply as
constants (excess emissions per cold start).
Evaporative emissions occur in a number of different ways. Fuel vapour is expelled from the
tank each time it is refilled, the daily increase in temperature (compared with overnight
temperatures) causes fuel vapour to expand and be released from the fuel tank, and vapour
is created wherever fuel may be released to the air, especially when the vehicle is hot during
or after use. There are therefore a number of different emission factors, e evaporative ,
depending on the type of evaporative emission. Generally, these factors are a function of the
ambient temperature and the fuel volatility. Similarly, a number of activity data are also
needed, including total distance travelled and numbers of trips according to the temperature
of the engine at the end of the trip.
These principles apply, with some exceptions, to all pollutants and vehicle types, but
different classes of vehicle behave differently and relationships between emissions and
operating characteristics vary for each pollutant. For that reason, an estimate of emissions
from mixed traffic must be made as a summation of emissions from each homogeneous
vehicle class in the traffic, and where the area studied contains roads with different traffic
behaviour, this must also be taken into account. And, of course, this must be done
separately for each pollutant.

Box 5.17: Basic principles of a typical road transport emission model.
132

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

The calculation method in the Design Manual for Roads and Bridges requires the user to
provide only limited input data. For each road under consideration, the average traffic flow
and speed, the percentage of heavy duty vehicles and the distance to the receptor position
must be specified.
Tables and graphs give estimates of the annual average traffic produced concentrations of
carbon monoxide, total hydrocarbons, total oxides of nitrogen and particles that would
result from a standard traffic flow (1000 vehicles/hour travelling at 100 km/h) at the
appropriate distance from the road.
The given traffic data are used with other data tables or graphs to calculate the equivalent
number of standard vehicles, and the concentration is adjusted for the actual flow
conditions.
The traffic derived pollution is added to a background figure and finally converted to match
the statistics of the National Air Quality Standards against which the results are evaluated.
Empirically derived conversion functions are given as follows:
❍ Carbon monoxide: Annual mean to maximum 8–hour mean
❍ Total hydrocarbons: Annual mean to annual mean benzene and 1,3–butadiene
❍ Total oxides of nitrogen: Annual mean to annual mean and 99.8 th percentile of hourly
mean nitrogen dioxide
❍ Particles: Annual mean to 90th percentile of daily means

Box 5.18: An outline of the air pollution calculation method of the DMRB.
likelihood that an air quality standard will be exceeded, and the methods used in the assessment
become more detailed and accurate at each stage.
The assessment procedure may involve pollution measurement, modelling or a combination of
the two.

5.6.1 Air pollution monitoring
Many techniques are available for the measurement of air pollutants. They range from the
estimation of particle concentrations from the darkness of a stain on a filter paper to complex
instruments capable of measuring multiple compounds continuously. It is not possible here to
describe the theory and operation of all of the methods in detail, but only to give some outlines
of the generic types of monitoring system and their typical applications.
Three main groups of equipment may be identified: sampling equipment by which the
compound of interest is stored for subsequent analysis in a laboratory; single point analysers
which continuously draw in air and measure the concentration of one or more pollutant; and
long path systems which measure the average concentration of one or more pollutants over a
certain distance. The choice of any particular monitoring strategy depends on its purpose and
is, of course, linked to its cost. Of the three types of equipment described, the sampling methods
are cheapest. Thus, they may be used in number to provide spatially discriminated data on
pollution levels over an area, but they are not capable of short term temporal resolution
(typically more than a day), and so cannot be used to measure the peak concentrations referred
to in many air quality standards. Continuous analysers are far more expensive in both capital
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

133

Traffic
Driver Behaviour
Vehicle Operations
Emissions
Air Quality

When a traffic management system is
introduced, its first effect will be on
drivers. They may take one of a number
of different actions such as changing
their route, journey times or mode of
transport, or simply continue their
previous practice. Whatever their
action, it will alter the way that vehicles
are operated, either their own vehicle if
they continue to use it on the same
route, or other vehicles if they divert or
change to another time or mode of
transport. As seen in section 5.4.1, a
change in vehicle operating conditions
can produce a significant change in its
emissions. Emissions from the traffic as a
whole will also be influenced by other
results of the management system that
may involve changes in the amount and
composition of the traffic. Changes in
emissions will then have an effect on
local air pollution concentrations.

Box 5.19: The sequence linking traffic management to air quality.

and operating costs, but they are able to measure in real time to provide data on concentrations
for any averaging period. Some of the more commonly used methods of measuring the
pollutants covered by the Air Quality Strategy are indicated in Box 5.14. Boxes 5.15 and 5.16
show examples of the equipment and their installations.
As well as the types of equipment to use, two other facets of any measurement campaign should
be considered carefully – the location(s) and duration of the measurement. Concerning the
position at which the measurements are taken, there are perhaps two main considerations.
Firstly, it should be noted that the concentrations of most pollutants decrease rapidly with
increasing distance from the source (see box 5.12). Therefore, when road traffic is the source,
the highest levels will be found at the kerbside 3 . However, local air quality impacts are usually
evaluated in terms of their potential to harm health, and for that it is necessary for people to be
exposed to the pollution. Thus, even though there may be high concentrations at the side of a
busy major road, it may be more appropriate to monitor the pollution further away if people live
and work in a more distant area. Indeed, the Air Quality Strategy states that:

“The objectives defined in the strategy apply to locations which are situated outside buildings
or man–made structures above or below ground and where members of the public are regularly
present and might reasonably be expected to be exposed over the relevant averaging period.”
For pollutants such as benzene and lead, where the objectives relate to annual average
concentrations, it is unlikely that a roadside location would represent typical levels of exposure.
3 There are exceptions, especially ozone and other photochemical oxidants, for which the highest concentrations are
often in rural areas. These pollutants are created by chemical reactions as their precursors disperse away from the
emission source. However, local actions will have little influence on such compounds.

134

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Traffic management and driver behaviour
1. Public perception of and response to traffic management systems. Some traffic management schemes (eg, urban
traffic controls, traffic calming) oblige drivers to modify their behaviour while others (for example, park and ride,
cycle routes) offer a choice. The success of this latter type depends on the extent to which the option is taken up.
2. Traffic management during high pollution episodes. Some management systems could take effect only when there
is a danger of an air pollution standard being exceeded. The infrequent and short term nature of the controls may be
more acceptable than their imposition in the long term.
Driver behaviour and vehicle operation
3. Low emission driving styles. Research findings on the effectiveness of modified driving patterns to reduce emissions
are inconsistent and there is little information on the conditions necessary to promote low emission driving styles.
4. Enhanced technologies for low emission vehicle operation. High emissions result from frequent and rapid changes
in speed. There may be potential for “drive–by–wire” technologies to promote smoother driving by modifying the
driver’s manual inputs.
5. Vehicle operating profiles. The operation of a vehicle significantly affects emissions and must be specified if
measurements or model results are to be representative. Studies have tried to define typical operating conditions, but
an objective of some traffic management systems is to make the operation of the traffic no longer typical.
Vehicle operation and emissions
6. Emission measurements. There is considerable scope for emission measurements to supplement the data already
available.
7. Response of future vehicle technologies to traffic management. Engines and emission control systems are
continually modified and improved to meet increasingly stringent standards. Their properties may differ from those of
existing vehicles.
8. Traffic composition. A satisfactory indication of UK average traffic composition can be obtained from registration
statistics and national transport surveys. However, there can be significant differences between traffic composition on
a local scale and the national average, and this may have a large effect on emissions.
9. Emission modelling and traffic management. Studies have suggested that the extrapolation of emission models
beyond the range of the data on which they were based rapidly increases their uncertainty. It may be better to use a
set of databases, each derived from tests relevant to the situations they will be used to evaluate.
10. Cold start emissions. Emissions from vehicles with cold engines are higher than when they are warmed up. A
number of traffic management options have an impact on parking and the number of times a vehicle is started with a
cold or warm engine.
11. Primary NO 2 emissions. The majority of oxides of nitrogen are emitted as nitric oxide, but there is uncertainty as
to the proportion emitted as nitrogen dioxide. If the amount of primary NO 2 is appreciable it could contribute
significantly to the atmospheric concentration (usually assumed to be produced by reactions in the atmosphere after
emission).
Emissions and air quality
12. Meteorology during high pollution episodes. Pollution responsive controls (see 2) rely on an advance warning of
a likely episode. On a day to day timescale, traffic and its emissions are fairly constant and the occurrence of high
pollution levels depends more on the meteorological conditions.
13. Evolution of background pollution levels. Background contributions to pollution are a significant proportion and
need to be taken into account in any assessment. National progress to lower emissions through tighter control
standards should give rise to reduced background concentrations in the future.
14. Sources of PM. Some pollution measurements suggest that proximity to traffic has a relatively small effect on
concentrations of particles, but emission inventories often attribute a large part of the emissions to road traffic. More
basic information on this topic is needed.
15. Air pollution modelling. Pollutant emission and dispersion models are subject to considerable uncertainty. The
TRAMAQ research findings should be used to improve pollution prediction models.
16. Subjective effects. In order to be fully effective, it is important that the effects of traffic management schemes are
perceived to be positive by members of the public as well as through objective measures.

Box 5.20: Projects proposed for the TRAMAQ research programme.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

135

Thus, in choosing a site for air pollution measurements, some compromise between the highest
pollution levels and the highest levels of exposure is often appropriate.
It can be seen in box 5.11, for example, that pollution concentrations at a single location may
vary considerably. The graphs in Box 5.11 show hourly average oxides of nitrogen concentrations
near the M4 motorway in the approximate range of 10 to 500ppb. Some of this variability is
because of changes in the emission source strength (that it, the traffic flow) at different times of
the day and some is the result of variations in the weather conditions and their influence on the
dispersion of the pollution. As a consequence, measurements made over a short time period may
not be representative of the more general conditions at a particular location. Furthermore, most
of the objectives of the Air Quality Strategy require measurements made over at least one year,
either because the limit value is expressed as an annual mean (for example, 1,3–butadiene) or as
a percentile of shorter period averages during a year (for example, PM 10 as the 90 th percentile of
daily means). That is not to say that short–term measurements cannot be useful for some purposes,
but for the characterisation of typical pollution levels they are not usually adequate.

5.6.2 Air pollution modelling
To calculate the concentration of an air pollutant at a certain location, it is necessary to model
its emission from any sources in the vicinity, its dispersion from the emission sources and, if it
is chemically reactive, its transformation in the atmosphere. For some pollutants there are
significant background concentrations onto which the local emissions are superimposed, and
for those compounds this also needs to be included in the estimation procedure.
The methods used to estimate pollutant emissions from road vehicles are all essentially
empirical. In principle, an amount of traffic (vehicle.kilometres) is multiplied by a pollutant
emission rate (grams per vehicle.kilometre) to determine the amount of the pollutant that is
emitted. To account for differences in the emission characteristics of different vehicle types, a
classification system is usually used that defines groups of vehicles with similar properties, and
because emissions vary according to the way the vehicles are operated, the emission rate is
often expressed as a function of one or more operational parameters. One formulation of these
principles was recently detailed in the European Commission’s MEET project (Hickman, 1999),
and this is shown as a typical example in Box 5.17.
The MEET method uses the average vehicle speed to indicate its operating condition. It is clear,
though, that a certain average speed may be achieved in many different ways. For instance, a
trip at 40 km/h could be driven at that speed constantly, at 80 km/h for half the time and at rest
for the remainder, or another combination of speeds and delays. Differences such as these can
influence rates of emission and some models attempt to refine the treatment of vehicle operation
by including other variables, such as the rate of acceleration, as well as the average speed.
After a pollutant has been emitted it spreads in the air, influenced by the wind and other
atmospheric properties, and if it is reactive, it will interact with other compounds. There are
many mathematical models available that attempt to simulate the processes of dispersion and,
in some cases, chemical reaction. The models vary in complexity from simple graphs and tables,
such as those in the Design Manual for Roads and Bridges 4 (Box 5.18), that allow calculations
to be made manually, to large and detailed computer programmes.
One of the most commonly used types of dispersion model is the Gaussian Plume model. This
assumes that the emission develops into a plume along the mean wind direction. As the
pollutant travels down wind, it spreads into the air, becoming more dilute. The resulting
concentration profile is regarded as Gaussian (a normal distribution) in the vertical and
4 Although this type of model is simple in operation, their development usually takes into account most of the features
of the more complex type. They only become simple because of the extensive pre–processing that is done by the model
developer rather than the user.

136

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Traffic management
measure
UTC system
for central area
traffic signals
Parking control on
major urban roads
Parking control
within urban areas

Park and ride

Central area
traffic restraint

Traffic calming
measures

Mass transit systems

Public transport
pricing policies
Car pooling

HOV lanes

Cycling and walking

Road tolls and
other charges

Likely effect on travel patterns
and vehicle emissions

Uncertainties

Reduction in fuel consumption by up to
18%, emissions by up to 15% in the central
area. Easier circulation may attract more
vehicles offsetting benefits.
Reduction in emissions of 1 to 17% on the
routes affected. The reduced congestion may
attract more vehicles.
Reduction in car share or mileage in the
central area by up to 40%. Outside this area
traffic may be redistributed so that benefits are
perhaps only up to 5%.
May in fact increase the number and
distance of car trips without some other form
of restraint.

Inadequate data on heavy duty
vehicles, motorcycles and
“dirty” vehicles.

The reduction in emissions in the controlled
area would be proportional to the volume of
traffic banned. Redistribution of traffic outside
the controlled area may negate effects.
Cause vehicles to travel less smoothly as they
negotiate the obstacles. Emissions and fuel
consumption per vehicle kilometre tend to
increase, but often partly offset by reduced
traffic flow.
May have little effect on car use without some
other form of restraint. Many passengers may
continue to use their cars to access the stations.
Bus travel may increase by 20–30% but many
of the new passengers are likely to transfer from
walking or cycling.
In theory could reduce mileage by 15–80%
depending on the willingness to share. The
number of cold starts and hot/warm soaks
would also be reduced.
Can increase vehicle occupancies, but there
is also evidence that the improved journey times
may increase mileage.
Large scope for shorter and potentially more
polluting journeys to be undertaken by cycling
or walking.
Area licensing schemes may reduce car share in
the central area by up to 50%. Outside car share
may increase slightly.

Inadequate data on heavy duty
vehicles, motorcycles and “dirty”
vehicles.
Uncertain impact on emissions due to
cold start and hot/warm soak periods.

More information on emissions from
buses required to assess the impact of
switching to travel by bus. Uncertain
impact on emissions due to cold start
and hot/warm soak periods.
Inadequate data on heavy duty vehicles,
motorcycles and “dirty” vehicles.

High variability in available data,
inadequate data on goods vehicles,
buses and motorcycles, effects vary for
different types of measure.
Uncertain impact on emissions due to
cold start and hot/warm soak periods.
More information on emissions from
buses required to assess the impact of
switching to travel by bus.
Uncertain impact on emissions due to
cold start and hot/warm soak periods.

Uncertain impact on emissions due to
cold start and hot/warm soak periods.
Uncertain impact on emissions due to
cold start and hot/warm soak periods.
Inadequate data on heavy duty vehicles,
motorcycles and “dirty” vehicles.

Box 5.21: The potential for traffic management to reduce vehicle emissions (from Cloke et al 1998).
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

137

These data are one
hour
average
concentrations
measured
at
a
roadside
site
in
London.
At
low
concentrations
of
NO X ,
a
large
percentage is in the
form
of
NO 2 .
However, as the NO X
level increases, the
percentage of NO 2
quickly falls. This is
because there are not
sufficient
oxidising
agents in the air to
react with all of the
NO.
Data from another site
near to the M4
motorway
further
demonstrate
this
i n t e r a c t i o n .
Measurements
are
arranged in order of
increasing NO X . At
low concentrations
the conversion to NO 2
is rapid, and is
accompanied by a
corresponding
decrease in O 3 . At
higher NOX levels,
though, there is little
increase in NO2
because the very low
O 3 concentration does
not allow further
oxidation of the NO.

Box 5.22: Examples of the conversion of nitric oxide to nitrogen dioxide.
horizontal directions, and can be calculated from the standard deviations. These are, in turn,
calculated from the distance from the source. One benefit of the Gaussian model is that it uses
rather simple meteorological input data – simply the mean speed and direction of the wind and
an atmospheric stability factor. Other, more complex models attempt to simulate complicated,
turbulent airflows and topography.
In selecting a suitable dispersion model for any application, the quantity and quality of
available input data should be borne in mind. In their guidance on model selection
(LAQM.TG3, see box 5.13), the Government state:
138

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Scenario

Road
traffic volume

Baseline
A
B
C
D
D1
D2
D3
D4
D5
D6

132
129
127
124
119
118
118
119
118
119
116

Congestion
(average
time delay)
111
105
101
87
71
70
69
69
70
68
67

Pollutant emissions
Carbon
dioxide
101
99
97
95
91
91
91
92
91
92
90

Particles
33
32
32
31
29
29
29
29
29
29
29

Oxides of
nitrogen
26
26
25
25
24
24
24
24
24
24
23

Box 5.23: Summary of impacts in England in 2010 (indexed to 1996=100).
“The choice of model is crucially dependent on the quality of input data available. It is not
necessarily helpful to invest in an expensive and time consuming advanced model if only
sketchy and inaccurate emissions and meteorological data are available.”
A second, obvious consideration is the purpose for which the model is to be used. If an estimate
of air pollution levels is the only purpose of a calculation, then the model should be
commensurate with the available data, and attempts should be made to obtain good quality,
accurate data. Often, though, a model will be used in a comparative evaluation of alternative
transport scenarios, and in that case it may be unnecessary to provide precise meteorological
data, but simply to test the alternatives using the same assumptions for each. While the absolute
accuracy of the results may be doubtful, the comparison will be valid. The most important
criterion by which the model should be chosen for this purpose is probably the level of detail
with which it treats the aspects of the scenarios that are to be assessed. For example, if changes
in the vehicle fleet are to be examined, the model must have a disaggregated emissions
database, if the modelled area has very complex terrain, the model should be capable of dealing
with detailed wind patterns, and so on.

5.7 Control and reduction of traffic pollution
5.7.1 Traffic management
The principles that can be applied to the control of traffic emissions follow from the general
observations in section 5.4.1. There, it has been seen that there are large differences in the
emissions from different types of vehicle and that the emissions from each vehicle vary
significantly depending on the way it is operated. These, and the fact that the emissions are also
proportional to the number of vehicles suggest three broad types of traffic management action
that may be effective:
❍ measures that influence the traffic composition;
❍ measures that modify the operation of the vehicles; and
❍ measures that restrict the amount of traffic.
There is, of course, a great deal of overlap between the different measures and policies. A
scheme to promote public transport may affect the composition of the traffic (replacing cars by
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

139

In central London in
2005, it is estimated
that almost 70% of
emissions of oxides of
nitrogen will be from
goods vehicles and
buses. Even in outer
London, where cars
make up more than 80%
of the traffic, their
contribution to NO X
emissions
is
only
around one third.

The
situation
for
particulate emissions is
almost the same, but in
this case the car
contribution is about
15% in inner, and 30%
in outer London.

Box 5.24: Estimated contributions to NO X and PM 10 emissions in London in 2005.
buses) and also the amount of traffic (because of the higher carrying capacity of the buses);
physical traffic calming, used to improve road safety, will change the operation of vehicles, but
it is well known also to reduce traffic flows and may alter its composition if some vehicle types
find the measures especially difficult to negotiate. On the other hand, it may sometimes be
necessary to use more than one measure to achieve a single objective: a policy to reduce car
traffic by increased charges (for parking, road tolls, and so on), may be ineffective without
supporting actions to provide alternative means of transport.
Evaluations of traffic management systems for their effectiveness to reduce air pollution have
not been extensive, and those that have been carried out have usually relied on models rather
than observations. Recently, though, mainly in an attempt to improve the information available
for local authorities to use in Local Air Quality Management, the DETR has embarked on an
extensive programme of research on transport and air pollution, known as TRAMAQ (Cloke et al
140

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

1998). The programme was designed following a review of existing information and comprised 16
related projects intended to fill the most important knowledge gaps. The 16 projects were further
subdivided according to their position in a defined sequence of interactions between traffic and
air pollution (Box 5.19), and are listed in Box 5.20. Much of the research is as yet incomplete and
it is not therefore possible to report its findings in detail. Nevertheless the reviews conducted in
the early stages of the programme have produced some useful results that will be refined and
supplemented in future years. Box 5.21 reproduces a summary table from one such review which
lists a number of common traffic management techniques and gives a broad estimate of their likely
effects on travel patterns and vehicle emissions.

5.7.2 The impact of reduced emissions on air pollution levels
Reducing the emissions from the traffic in a particular location will not give rise to a directly
proportional reduction in pollution concentrations. In most cases the impact on pollution levels
will be considerably less. This is for two main reasons: traffic is not the only source of the
pollution and, for chemically reactive pollutants, their concentrations are influenced by their
reactions. These effects are perhaps of greatest importance for nitrogen dioxide and particle
concentrations, but apply to a greater or lesser extent to all pollutants.
Nitrogen dioxide, as noted in Section 5.4.2, is formed mainly by the oxidation of nitric oxide
emissions and near to roads, where there is an excess of nitric oxide, the concentration is often
limited by the availability of atmospheric oxidants, of which ozone is the most important. The
effect is shown in two ways in Box 5.22, using data from sites operated by TRL on behalf of the
Highways Agency.
Concerning particles, the main reason why traffic emission reductions do not produce
commensurate changes in pollution levels is that there is a substantial contribution from
non–traffic sources. In broad terms, at an urban location, about one third of the particulate
pollution is from nearby traffic and changes to the traffic will not immediately alter the other
two thirds.
The precise relationship between a change in emissions and its effect on air quality will vary
from location to location depending on the particular circumstances. However, a rough
estimate can be made using the calculation procedure from Volume 11 of the Design Manual
for Roads and Bridges. Taking a road with an arbitrary flow of traffic, and successively halving
the flow and repeating the calculation effectively simulates the successive halving of
emissions. This exercise suggests that a halving of emissions will result in reductions in
pollution levels of between 20% (for particles) and 35% (for the primary pollutants, carbon
monoxide, benzene and 1,3–butadiene). Considering again the potential for traffic
management measures to reduce emissions (Box 5.21) in conjunction with these broad
estimates suggests that the most effective types of management might produce reductions in
pollution concentrations of the order of 10%.

5.8 Practical measures to reduce traffic pollution
It has been seen that road vehicle emissions are influenced by many factors, including:
❍
❍
❍
❍

the
the
the
the

type of vehicle;
fuel used;
level of emission control, and
conditions under which it operates

Furthermore, atmospheric dispersion, dilution and chemical reactions modify the impacts of the
emissions on levels of air pollution.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

141

These basic observations have been used to suggest a number of general policies and principles
that should be applied to minimise the impacts. Firstly, a range of options are available to
reduce traffic emissions, and secondly, the impact of the emissions can, in some circumstances,
also be reduced.

5.8.1 Emission reduction measures
Perhaps the most obvious way to reduce traffic emissions is to reduce the amount of traffic, and
a number of policies can be pursued with that objective. In January 2000, the Department of the
Environment, Transport and the Regions published its first report under the Road Traffic
Reduction (National Targets) Act, 1998. The report considers a number of scenarios designed to
slow down, and eventually halt the growth of traffic, and thus illustrates a wide range of traffic
reduction measures. Each scenario combines a number of actions that focus on different aspects
of transport:
❍ Land use planning – shifting household growth towards denser urban settlements
❍ Local actions
❍ promoting alternative modes
❍ reallocation and / or reduction of parking and road capacity
❍ workplace parking charges, cordon charges, increased parking charges
❍ traffic management
❍ local land use planning
❍ promoting awareness
❍ Sustainable distribution – improved freight transport logistics
❍ Passenger rail enhancements
❍ Targetted road use charges
❍ Targetted increases in motorway and trunk road capacity
❍ Increases in fuel duty
Scenarios A, B, C and D (Box 5.23), are successively more intensive, but each focuses heavily
on local actions. Scenarios D1 to D6 supplement scenario D by adding one or more additional,
more widespread action (for example, road charging outside urban areas, increases in fuel duty
and much higher investment in railways). Scenario D6 combines all of the measures considered.
Box 5.23 sets out the effects of these scenarios, estimated for 2010, on traffic volume,
congestion and pollutant emissions. Congestion, as indicated by the average delay per vehicle,
is reduced by the most extreme scenario by almost half; reductions in traffic volume and
pollutant emissions are a little over 10%.
Whatever the amount of traffic in circulation, it can be made less polluting through a variety of
measures. Those that may be used to influence the composition of the traffic include, for
example, lorry bans or weight restrictions, the promotion of public transport, park and ride
schemes and restrictions on car traffic. Local authorities, through traffic regulation orders, can
place restrictions on all, or any class of vehicles, defined according to any characteristic. It is
important that the effects of any such action be carefully considered. The private car is often the
natural target for restriction and, in many ways, reducing car traffic could give benefits (reduced
congestion, improved safety and amenity). However, it is not necessarily the case that restricting
cars will give the greatest reductions in emissions. In Box 5.9 it is shown, for example, that bus
particulate emissions are more than ten times higher than from a petrol car. Similarly in a study
of a low emission zone for London, Cloke et al (2000) showed that the largest contributions to
emissions of oxides of nitrogen and particles in 2005 in London would be from buses and goods
vehicles (Box 5.24), even though they make up less than 20% of the traffic.
As well as control of the basic vehicle types in the traffic, it is possible to promote cleaner
sub–classes in a number of ways, such as:
142

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

❍ Cleaner local vehicle fleets. Local authorities are encouraged by the Government to
establish Quality Partnerships with bus operators and freight carriers. In return for the
provision of improved facilities, the authority may require that vehicles reach a certain
environmental standard. Similarly, contracts for local authority services (for example,
refuse collection, school transport) could be awarded, in part, on the basis of the
emission standard of the vehicles used.
❍ Promotion of “city” fuels. Even older vehicles can benefit from the use of modern fuels
manufactured to a high specification. One of the main objectives of the latest fuel
standards is to reduce sulphur levels. This can have a direct beneficial effect on
emissions, but also increases the effectiveness and durability of exhaust aftertreatment
systems (catalysts and particulate traps).
❍ Emission control standards. The standard to which a vehicle is type approved is a good
indicator of its relative emissions performance (see Box 5.5), and may also be used as a
criterion for control. The principle might be used in specifying access rights within a low
emission zone, qualification to participate in a quality partnership, to compete for local
authority contracts, and so on. Regular vehicle maintenance can help to maintain the
emission standard of a vehicle in use. This can be promoted through educational
campaigns, roadside emission checks and incentives to motorists to have their vehicles
checked, perhaps involving local businesses such as supermarkets (who have allowed
their car parks to be used by motoring organisations) and garages (who may offer
promotional cut–price services).
❍ Incentive schemes. There are a number of ways in which older vehicles may be modified
to reduce their emissions. Aftertreatment systems exist that can be retrofitted to
non–catalyst petrol vehicles that bring their performance almost to the Euro 1 level;
particulate traps may be retrofitted to diesel vehicles, and many types of vehicle can be
modified to operate using alternative fuels such as CNG and LPG. However, because of
the relatively low value of the vehicles for which these would be beneficial, it is likely
that their widespread adoption would require some form of incentive. The incentive
could be financial, or one of the forms mentioned earlier, such as qualification for access
into a restricted area. An alternative to retrofit systems is prematurely to scrap older
vehicles, to accelerate the rate at which newer technologies penetrate the vehicle fleet.
The introduction and maintenance of a clean vehicle fleet is important. Technological
improvements to vehicles and fuels have been the single most effective means of controlling
and reducing traffic derived pollution. But the performance even of a clean fleet can be further
improved by constraining its operations. Emissions are at their lowest when vehicles are
operated at moderate speeds as smoothly as possible. For example, early work by Joumard et al
(1989) showed that, at speeds characteristic of urban driving, emissions at a constant speed
were of the order of a half of those at the same average speed but with the normal accelerations,
decelerations, stops and starts found in urban traffic. Many types of traffic management scheme
have been considered with the objective of reducing emissions by smoothing the progress of the
traffic, and a number have been mentioned in the context of the TRAMAQ programme (section
5.7.1).
As noted, there is considerable overlap between the various traffic management options that are
available, and many of the traffic reduction measures and controls on the traffic composition
may be included in this general category. There are also, though, types of traffic management
that affect principally the movement of the vehicles rather than their number or types.
Perhaps the most widely used are urban traffic control systems which control traffic light
sequences to optimise flows at junctions. These may be of two basic types: those with a fixed
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

143

series of time delays and those whose time delays vary in real time in response to the traffic
conditions. The first type is typified by the TRANSYT system (Robertson et al 1980), and the
second by SCOOT (Hunt et al 1981). Coordination of signals using systems of this type has been
shown to reduce delays, fuel consumption and emissions, with benefits improving as the system
becomes more adaptive. A normal SCOOT system is likely to reduce emissions by around 10%
to 20%, and coordination especially for emission control can give an additional benefit of two
to four percent.
A second type of management procedure of this general type is a priority system for certain
types of vehicle. Bus and cycle lanes are becoming common, sometimes also permitting use by
taxis, and a small number of dedicated lanes for high occupancy vehicles have been piloted.
Further priority can be given at junctions, using systems to detect the favoured type of vehicle
and allow it to proceed more quickly than others. The emissions benefits from such priority
schemes appear to be very uncertain, and sometimes negative. The main reason for this is that,
by giving priority to a particular vehicle type, a scheme is almost certain to cause extra delays
to the rest of the traffic. Since the preferred vehicles are usually only a minority of the traffic,
their gains are often outweighed by the effects on the remainder of the traffic. A related type of
measure is the limitation and control of roadside parking. In the same way as the provision of a
dedicated lane allows certain vehicles to progress more smoothly, the release of road space
formerly occupied by parked vehicles eases the circulation of the traffic, but in this case the
effect is on all vehicle types, so delays, fuel consumption and emissions tend to reduce.
Finally, in this group of measures, are the imposition and enforcement of speed limits. The
benefits from better control of speeds are probably greatest on roads carrying high speed traffic,
and two aspects will be considered. Perhaps counterintuitively, congestion on motorways can
be relieved by reducing the speed limit. This has the effect of delaying the onset of flow
breakdown, by reducing the likelihood of high speed traffic encountering convoys of slower
vehicles. The principle has been exploited in the installation of a variable speed limit system on
a 20km section of the M25 motorway. Depending on the flow conditions, reduced speed limits
of 40, 50 or 60mph may replace the normal national limit. The main reason for introducing the
system was to improve safety, but it has also been evaluated for its effect on emission rates.
Barlow (1997) estimated that emissions were reduced by the order of 10%. However, as with all
types of traffic management that reduce congestion, there is a risk that additional traffic will be
attracted by the improved situation.
Another aspect of speed control that may be of increasing importance is that of vehicles
travelling at very high speeds, although there is at present little quantitative information
available. In order to be effective, the catalysts on modern petrol vehicles need to be supplied
with exhaust whose composition is carefully controlled to contain a balance of oxidising and
reducing compounds. This is not possible when there is a very high power demand on the
engine, as extra fuel needs to be supplied. In limited tests, Vidon et al (1998) found rates of
emission to be very high under high engine loads. Carbon monoxide emissions were 200 to
20,000 times higher for loads greater than 75% of the maximum, and those of oxides of nitrogen
were ten times higher. Over the motorway test cycle they used, about 90% of the carbon
monoxide emissions occurred during only 15% of the time.

5.8.2 Reducing the impact of the emissions
Irrespective of all controls, road traffic will continue to produce emissions and in some
circumstances, albeit with reducing frequency, is likely to produce, or add to, air pollution
problems. It is therefore worth recalling that the link between the emissions and the
concentrations to which people are exposed is their dispersion in the air, under the influence of
the meteorological conditions.

144

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

It is a simple principle that, whatever the weather, concentrations tend to reduce with
increasing distance from the point at which the pollution is emitted. This fact suggests another
group of pollution control measures based on the separation of people and sensitive ecologies
from road sources. A bypass, for example, although it may be longer than a direct route through
a town or village and, consequently, may give rise to more emissions than the direct route, can
be beneficial in terms of its air quality impacts by reducing the exposure of the people in the
conurbation. As shown in section 5.4.2, concentrations can fall substantially over relatively
small distances, and careful alignment of roads can enable the avoidance of high levels in
locations where people are exposed. This may be particularly helpful if those involved are among
the more susceptible of the population (for example children at school or those in hospitals).
Further protection can be provided by screening belts of vegetation. Plants, especially dense
bushes and trees, remove some pollutants from the air by physical deposition onto their leaves
and other parts. Additionally, some gaseous pollutants are taken up by the plants during
transpiration. To be effective, though, it is necessary for planting to be rather extensive.
A final consideration is that periods of high pollution are caused primarily when the weather
conditions are adverse. On a day to day timescale, flows of traffic and their resulting emissions
are relatively constant. Pollution concentrations on the other hand may vary by an order of
magnitude or more. The highest concentrations occur usually during still winter days when the
reduced dispersion of the emissions allows them to build up in the air near to where they were
released. While this phenomenon does not, in itself, offer a control mechanism, it demonstrates
one of the ways in which control mechanisms may be deployed. If it is possible reliably to
predict the occurrence of a period of high pollution, measures could be implemented to reduce
emissions only at the times when there is a risk of poor air quality. Because this is likely to occur
only a few times a year, the measures could be more extensive and restrictive than would be
acceptable at all times of the year. Perhaps the greatest challenge in this respect is to predict the
pollution episode early enough to give sufficient warning for people to change their travel
plans, and for authorities to activate their control measures.

5.9 Principal recommendations
Since it was first recognised as a serious problem, major advances have been made in
understanding and controlling traffic–produced air pollution. In spite of an increase in road
traffic since 1970 of more than 100%, emissions and air pollution levels are lower now than
they were then. Nevertheless, concentrations of some pollutants are still sometimes higher than
air quality standards and traffic levels will continue to increase unless there is a major reversal
of the long–term trend. It is therefore important to continue to develop cleaner vehicle
technologies and to operate them in ways that impose the least environmental damage. Many
of the methods by which this might be done will be specific to a particular locality, vehicle type,
transport operation and so on, but there are a number of general principles that can guide
pollution control plans and policies.
Clean technologies
Continued efforts should be made to develop and promote cleaner vehicles and fuels.
❍ Historically, the most effective procedure has been the imposition of increasingly
stringent emission limits. Manufacturers are then required to meet the limits, but no
specific technology is obligatory. This allows further developments of traditional engines
and emission control systems, but also more innovative applications of alternative fuels
and engine types.
❍ While systems are available that can substantially reduce the emissions of toxic
pollutants, all fossil fuel combustion produces carbon dioxide and contributes to the
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

145

greenhouse gases in the atmosphere. For example, while an electric vehicle may be
sometimes termed a “zero emission” vehicle, this is rarely the case since the electricity
is usually generated by a combustion plant. It is therefore important in the development
of clean vehicles that their life cycle emissions, including those from the fuel production
be taken into account. If electric vehicles are promoted, there should also be investment
in renewable energy sources such as tidal, solar, wind and hydro–electricity production.
Efforts should also be made to improve the fuel economy of traditional vehicle types.
Improved assessment procedures
Most of the measures that can be implemented to reduce traffic pollution have both positive and
negative impacts and should be evaluated carefully and objectively before application. A few
examples of this type of conflict are 5 :
❍ Dedicated road space: Lanes are frequently dedicated to certain types of vehicle (for
example, buses, high occupancy vehicles), and this may be associated with other
measures such as priority at signal controlled junctions. This will improve journey times
and reduce fuel consumption and emissions from the vehicles given priority, but will
have the opposite effect on other traffic. As the priority vehicles are almost always a
minority of the traffic, the overall result may be a worsening of the situation.
❍ Increased public transport: Each public transport vehicle, because of its size, uses more
fuel and creates more pollution than a car. It is clear that public transport is less polluting
than the equivalent amount of travel by car only if high occupancy levels can be
consistently maintained.
❍ Traffic management to reduce congestion: This will, in the short term, produce lower
emissions. However, easier driving conditions may attract more traffic and reverse the
effect.
❍ Retrofit particulate traps: These are now reasonably common on heavy–duty diesel
vehicles. They are very effective in reducing particulate emissions, but have no effect on
other pollutants or on fuel consumption. If the use of a retrofit system encourages the
extended use of older engines, it may be less beneficial than the encouragement of newer
engines with improved control for all pollutants.
Control of traffic and transport
Transport operations are frequently inefficient, and fuel consumption and emissions could be
reduced by better optimisation. For example:
❍ Many lorries carry a load from their origin to destination but return empty (on average,
about 30% of lorry mileage is without a load).
❍ Better coordination of timetables and provision of more, and more accurate, travel
information could make public passenger transport attractive to a greater number of
people.
❍ Greater restrictions of on–street parking could reduce delays to other vehicles and
produce less polluting driving patterns.
❍ Aggressive and high speed driving produces high rates of emission. Improved training and
greater awareness, better enforcement of speed limits, or the more widespread use of
speed limiters (and perhaps acceleration limiters) on vehicles could all be beneficial.
5 In giving these examples, it is not intended to imply that these measures are ineffective, but only to point out that
their potential disbenefits should not be ignored during an evaluation

146

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Traffic reduction
There is an obvious link between the amount of traffic and the pollution it produces.
❍ Reducing the amount of traffic would reduce congestion and allow the remaining traffic
to use the road space more efficiently.
❍ In the longer term, land use planning could help to change the numbers of journeys
needed and their distances.
❍ In the shorter term, many transport policies and traffic management procedures could be
configured to discourage journeys or make alternative travel modes available.

References
Advisory Committee on Trunk
Road Assessment, 1977

Report of the Advisory Committee on Trunk Road Assessment.
(The “Leitch Report”). HMSO, London.

Bosch, Robert GmbH, 1993

Automotive Handbook (3rd Edition). Stuttgart.

Broughton GFJ, JS Bower,
H Clark and PG Willis, 1998

Air pollution in the UK: 1996. AEA Technology, Culham.

Cloke J, JA Cox, AJ Hickman,
S D Ellis, M J Ingrey and
K Buchan, 2000

A low emission zone for London. Report 431, Transport
Research Laboratory, Crowthorne.

Cloke J, P Boulter, GP Davis,
Traffic management and air quality research programme.
A J Hickman, R E Layfield,
Report 327, Transport Research Laboratory, Crowthorne.
IS McCrae and PM Nelson, 1998
Department of the Environment, The United Kingdom National Air Quality Strategy. The
Welsh Office and
Stationery Office, London.
Scottish Office, 1997
DETR, 2000
Tackling congestion and pollution. DETR, London.
Department of the Environment, The Air Quality Strategy for England, Scotland, Wales and
Transport and the Regions,
Northern Ireland. The Stationery Office, London.
the Scottish Executive, the
National Assembly for Wales and
the Department of the Environment
in Northern Ireland, 2000
Department of Transport, 1977

Route location with regard to environmental issues. (The
“Jefferson Report”).

Department of Transport, 1982

Manual of Environmental Appraisal. The Stationery Office,
London.

Department of Transport, 1993

Design Manual for Roads and Bridges, Volume 11 –
Environmental Assessment. The Stationery Office, London.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

147

148

Expert Panel on Air Quality
Standards, 1994a

Benzene. HMSO, London.

Expert Panel on Air Quality
Standards, 1994b

Ozone. HMSO, London.

Expert Panel on Air Quality
Standards, 1994c

1,3–butadiene. HMSO, London.

Expert Panel on Air Quality
Standards, 1994d

Carbon monoxide. HMSO, London.

Expert Panel on Air Quality
Standards, 1995a

Sulphur dioxide. HMSO, London.

Expert Panel on Air Quality
Standards, 1995b

Particles. HMSO, London.

Expert Panel on Air Quality
Standards, 1996

Nitrogen dioxide. HMSO, London.

Expert Panel on Air Quality
Standards, 1998

Lead. HMSO, London.

Expert Panel on Air Quality
Standards, 1999

Polycyclic aromatic hydrocarbons. HMSO, London.

Hickman AJ, 1989

Measurement of particulate lead on the M4 motorway at
Harlington Middlesex (Fifth Report). Research Report 184,
Transport and Road Research Laboratory, Crowthorne.

Hickman AJ, 1999

MEET – methodology for calculating transport emissions and
energy consumption. Office for Official Publications of the
European Commission, Luxembourg

Hitchcock G, T Parker,
J Longhurst and A Simmons,
1999

Reducing the environmental impact of vehicles in urban
areas. Low emission zone concepts. Transport and Travel
Research Ltd., Bristol

Hunt PB, DI Robertson,
RD Bretherton and RI Winter,
1981

SCOOT – a traffic responsive method of coordinating signals.
Report LR 1014. Transport and Road Research Laboratory,
Crowthorne.

Joumard R, L Paturel, R Vidon,
J–P Guitton, A–I Saber and
E Combet, 1989

Emissions unitaires des véhicules légers français. Report NNP
8907. INRETS, Bron.

Robertson DI, CF Lucas and
RT Baker, 1980

Coordinating traffic signals to reduce fuel consumption.
Report LR 934. Transport and Road Research Laboratory,
Crowthorne.

Salway AG, HS Eggleston,
JWL Goodwin, JE Berry and
TP Murrells, 1999

UK emissions of air pollutants 1970 – 1996. Report AEAT
3092, AEA Technology, Culham.

Vidon R, C Pruvost and
P Tassel, 1998

Evaluation de la dispersion des measures d’émissions de
polluants sur différents cycles. Report LEN 9804. INRETS,
Bron.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

C HAPTER 6. N OISE M ANAGEMENT
6.1 Introduction
6.1.1 The extent of the problem
Road traffic is the most dominant source of community noise in England and Wales. In a
national noise survey undertaken in 1990 (Building Research Establishment, 1993) it was
concluded that around 90% of the population of England and Wales hear traffic noise from their
homes.
Despite the very large proportion of the population affected by road traffic noise, a 1998 DETR
survey charting trends in formal complaints in England and Wales demonstrated that relatively
few complaints were associated with road traffic noise.
This can be explained, in part at least, by a general perception that noise is an inevitable byproduct of the private ownership of motor vehicles and an extensive road network. The freedom
of mobility this brings is generally perceived to outweigh the adverse impact of environmental
noise to society as a whole. Despite this, it is commonly accepted that noise from road traffic
is not welcomed and should preferably be reduced. For this reason much effort has been
expended over the past few decades in developing means of reducing environmental noise
radiation from road traffic: it is the focus of these efforts, particularly directed towards the
management and maintenance of highways, that provides the input for this chapter.
Complaint Type
Domestic
Industrial and commercial
Road works & construction
Road Traffic
Aircraft

Number of complaints per million people
1983–1984

1993–1994

1994–1995

1995–1996

1,016
595
81
36
17

3,468
1,120
168
59
64

3,949
1,320
300
60
111

4,895
1,466
229
66
48

Table 6.1: Reported number of complaints per million population in England & Wales
categorised into different noise source types.
6.1.2 Sources of road traffic noise
Sources of noise from road vehicles can be separated into two distinct components: those
associated with the engine, transmission and exhaust systems, and those associated with the
interaction of the tyres on the road surface. At lower traffic speeds of up to around 40km/hr the
engine, transmission and exhaust sources tend to control the radiated noise levels. The
magnitude of these sources are all related to engine speed. At higher traffic speeds, the tyre
noise becomes increasingly dominant. The magnitude of this source of noise is related to
vehicle speed. Therefore in urban environments a combination of engine, exhaust and tyre
noise dominates, whilst on free flowing open roads tyre noise generally dominates. This is with
the exception of HGV noise which can still be dominated by diesel engine related noise, even
at relatively high vehicle speeds.

6.1.3 Trends in road traffic noise
Over the past two decades significant advances have been made in reducing levels of noise
radiated from road vehicles (Commission of the European Communities, 1996). Individual cars,
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

149

for instance, have seen a reduction in permissible noise levels, as measured in accordance with
standard type–approval limits, of 8dB(A) over this period, whilst for HGVs the reduction has
been 11dB(A).
Vehicle Type
Cars
HGV’s

Year of Directive
1980

1993

1996

82dB(A)
91dB(A)

77dB(A)
84dB(A)

74dB(A)
80dB(A)

Table 6.2: Maximum permissible noise levels of road vehicles based on EC Directives, as
measured in accordance with standard type–approval tests.
Advances in vehicle low noise technology have been assisted by the introduction of additional
noise mitigation measures such as roadside barriers, quieter road surfaces and the introduction
of planning policies guarding against the juxtaposition of noisy roads and noise sensitive
accommodation. However, the reductions in road traffic noise levels experienced by the general
population have not seen anywhere near the overall reductions implied from the increasingly
stringent legislation. Instead, whilst the number of people exposed to very high traffic noise
levels has decreased, a gradual increase in the total number of people exposed to lower traffic
noise levels has been observed (Flindell, 1996).

6.1.4 Impact of road traffic noise
Environmental noise heard by people inside or outside their homes can have a number of
adverse effects. The main effect is annoyance, but secondary effects such as a reduction in
property values can also be important.
If authorities responsible for the provision and regulation of transport systems are to exert any
control over environmental noise they must define acceptability criteria to form a basis for
environmental assessment, or alternatively as a “trigger” for compensation schemes. Human
response to noise is therefore an important consideration in situations concerning road traffic
noise. However, obtaining a complete understanding of the relationship between noise
exposure, annoyance and possible adverse health effects is a complex problem, as annoyance
depends as much on the attitude and activity of the exposed individual (sleeping, watching
television, working and so on) as it does on the level of noise exposure.

6.2 Measurement of road traffic noise
6.2.1 Definition of noise
The standard definition adopted here is that “noise” is sound unwanted by the recipient.
Consequently the two terms “sound” and “noise” can be used interchangeably from a physical
viewpoint, but subjectively they evoke quite different responses.

6.2.2 Measuring noise
The primary purpose of measuring environmental noise is to assess its impact on people.
Consequently, any sound–measuring device employed for the task should provide a simple
readout that relates the objectively measured sound to human subjective response. To achieve
this the instrument must, as a minimum, be capable of measuring sound over the full range
detectable by the human ear.
Perceived sound arises from the response of the ear to sound waves travelling through the air.
Sound waves comprise air molecules oscillating in a regular and ordered manner about their
150

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

equilibrium position. The speed of the oscillations determines the frequency, or pitch, of the
sound, whilst the amplitude of oscillations governs the loudness of the sound. A healthy human
ear is capable of detecting sounds at all frequencies from around 20Hz to 20kHz over an
amplitude range of approximately 1,000,000 to 1. Even relatively modest sound level meters are
capable of detecting sounds over this range of amplitudes and frequencies, although the
accuracy limits of sound level meters vary depending on the quality of the unit (BS5969, 1981).
When undertaking measurements of road traffic noise, as with all other noise measurements, it
is important to select a measurement system that possesses the relevant accuracy tolerances and
is calibrated to a known standard.
Whilst measurement systems exist that are capable of detecting the range of sounds detected by
the human ear, the complexities of human response to sound make the derivation of subjective
response from a simple objective measure an intractable problem. Not only does human
response to sound vary from person to person, but it can also depend on the activity and state
of mind of an individual at the time of the assessment. In practice a complete range of responses
to any given sound may be observed. Thus any objective measure of noise can at best be used
to infer the average subjective response over a sample population.

6.2.3 Sound levels and decibels
Because of the broad amplitude range covered by the human ear, it is usual to quantify the
magnitude of sound using the decibel scale.
When the amplitude of sound pressure is expressed using decibels (dB), the resultant quantity
is termed the sound pressure level. The conversion of sound pressure in Nm -2 to sound pressure
level in dB reduces the range from 0dB at the threshold of hearing to 120dB at the onset of pain.
Being represented on a logarithmic amplitude scale, the addition and subtraction of decibel
quantities does not follow the normal rules of linear arithmetic. For example, two equal sources
acting together do not produce a combined level of 80dB. Instead they produce a sound level
3dB higher than either source acting individually. So, for example, 40dB+40dB=43dB and
50dB+50dB=53dB. The following Tables 6.3(a) and (b) provide a tabular reference for the
addition of decibels both in terms of adding two sources of different relative levels and in terms
of adding multiple sources each of the same level.
Level due to noise
source “A”
X
X
X
X
X
X
X
X
X

dB
dB
dB
dB
dB
dB
dB
dB
dB

Level due to noise
source “B”

Combined level of
“A” and “B”

X – 10 dB
X – 5 dB
X – 3 dB
X – 1 dB
X dB
X + 1 dB
X + 3 dB
X + 5dB
X + 10 dB

X + 0.4 dB
X + 1.2 dB
X + 1.8 dB
X + 2.5 dB
X + 3.0 dB
X + 3.5 dB
X + 4.8 dB
X + 6.2 dB
X + 10.4 dB

Table 6.3(a): The effect on the total sound pressure level, in decibels, of combining two
separate noise sources of different relative levels.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

151

Level due to
each noise source
X
X
X
X
X
X
X
X
X
X

dB
dB
dB
dB
dB
dB
dB
dB
dB
dB

Number of noise sources

Combined level of
“A” and “B”

1
2
3
4
5
6
7
8
9
10

X + 0.0 dB
X + 3.0 dB
X + 4.8 dB
X + 6.0 dB
X + 7.0 dB
X + 7.8 dB
X + 8.5 dB
X + 9.0 dB
X + 9.5 dB
X + 10.0 dB

Table 6.3(b): The effect on the total sound pressure level, in decibels, of combining different
numbers of equal noise sources.
An increase in sound pressure level of 3dB is commonly accepted as the smallest change of any
subjective significance. An increase of 10dB is often claimed to result in a perceived doubling
in loudness, although the basis for this claim is not well founded. An increase of 3dB is
equivalent to a doubling in sound energy, which is the same as doubling the number of similar
sources. An increase of 10dB is equivalent to increasing the number of similar sources tenfold.
Putting these numbers into perspective, it requires a doubling in the volume of traffic using a
road to increase the noise level by 3dB.

6.2.4 Frequency selectivity of human hearing and A–weighting
Whilst the ear can detect sounds over a frequency range extending from 20Hz to 20kHz, it is
not equally sensitive at all frequencies. Human hearing is most sensitive to sounds containing
frequency components lying within the predominant human speech frequencies from around
500Hz to 4000Hz. This frequency range also covers a significant part of the road traffic noise
spectrum.
When measuring sound with the aim of assessing subjective response, the frequency selectivity
of hearing must be accounted for by reducing the contributions of lower and higher frequency
sounds. This is achieved by using an “A”–weighting filter. The resultant sound pressure level is
referred to as the A–weighted sound pressure level, denoted LpA or dB(A) for short. In terms of
specifying an easy to use metric for assessing the subjective response to road traffic noise, the
A–weighted sound pressure level is the best general measure.

6.2.5 Temporal variation of noise and noise indices
The simple A–weighted sound pressure level provides a snapshot of the noise environment at
any given moment in time. However, noise levels can vary from second to second as individual
vehicles pass by the measurement point, through daily rush hour trends and seasonal trends due
to holiday traffic, right up to trends observed over several years resulting from a gradual change
in traffic using the road in question.
A single number indicator is required that best quantifies subjective response to traffic noise.
The question thus arises as to how temporal variations in level should be accounted for when
assessing traffic noise. This is achieved in practice by selecting a representative time period and
calculating either the average noise level over the time period or the noise level exceeded for a
stated proportion of that time period.
152

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

6.2.6 Equivalent continuous sound level, L Aeq,T
The equivalent continuous sound level averages out any fluctuations in level over time. It is
formally defined as the level of a steady sound which, in a stated time period and at a given
location, has the same sound energy as the time varying sound. The equivalent continuous
sound level is expressed L Aeq,T in dB, where the A–weighting is denoted by the subscripted
“A”. The “T” refers to the time period over which the averaging is performed. The L Aeq,T is a
useful “general” index that correlates well with subjective response to most types of
environmental noise, although different sources can evoke different responses for the same
L Aeq,T noise level.
The disadvantage of the equivalent continuous sound level is that it provides no information as
to the temporal variation of the sound. For example, the same L Aeq could result from a
continuous sound of moderate level as it could from a single burst of loud sound superimposed
on an otherwise continuous low level sound. This problem is particularly acute where the
general ambient noise level is relatively low, such as may occur at longer distances from roads.
Examples of extraneous noise that often corrupt L Aeq,T noise measurements in such instances
can include birdsong or a dog bark near to a noise monitoring point, or an occasional overflying
aircraft or a sudden gust of wind. Despite this shortcoming, the L Aeq,T index is becoming
increasingly adopted as the unit of choice for both UK and European guidance and legislation.
This choice is often as much for reasons of commonality between standards as it is for
overriding technical arguments. In the Government’s current planning policy guidance notes the
L Aeq,T noise level is the index used for the assessment of environmental noise. This assessment
is undertaken separately for daytime (L Aeq,16hr, 07:00 to 23:00) and night time (L Aeq,8hr, 23:00
to 07:00) periods.

6.2.7 Percentile exceeded sound level, L An,T
Unlike the L Aeq,T index, percentile exceeded sound levels provide some insight into the
temporal distribution of sound level throughout the averaging period. They are defined as the
sound level exceeded by a fluctuating sound level n% of the time of a specified time period, T.
They are denoted by L An,T in dB, where “n” can take any value between 0% and 100%.
The L A10,T and L A90,T indices are the most commonly encountered percentile noise descriptors
used in the UK.
The traditional index adopted for road traffic noise is the L A10,T . This index is useful because
traffic noise is not usually constant, but rather it fluctuates with time as vehicles drive past the
receptor location. The L A10,T index gives the noise level exceeded for 10% of the time over any
given time period, T. It therefore characterises the dominant peaks in the noise as vehicles drive
past, rather than the lulls in noise between the vehicles, provided vehicle noise is present for at
least 10% of the time. The linear average of the 18 L A10,1hr noise levels measured for each hour
between 06:00 and 24:00, denoted L A10,18hr, is the index traditionally used to assess traffic
noise exposure for the purposes of determining the need for sound insulation to any dwelling
exposed to traffic noise. For environments dominated by road traffic noise the L Aeq,16hr noise
level measured from 07:00 to 23:00 is usually found to be approximately 2dB(A) lower than the
L A10,18hr noise level evaluated between 06:00 and 24:00.
The L A90,T noise index is the noise level exceeded for 90% of the time period, T. It provides an
estimate of the level of continuous background noise, in effect performing the inverse task of
the L A10,T index by detecting the lulls between peaks in the noise. The L A90,T index can
therefore prove useful when measuring the relatively constant and continuous low level of road
traffic noise at large distances from busy roads, particularly as the index automatically excludes
short term noise peaks not associated with the distant road.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

153

6.2.8 Temporal variations outside the noise index averaging periods, “T”
Averaging traffic noise levels over the 16 or 18 hour periods thus far considered can successfully
account for variations in traffic noise during the course of individual days. Some variations,
however, exhibit trends over longer periods. Seasonal traffic variations, for instance, may result
in heavy traffic flows during holiday periods. This being a predictable trend it is possible to
ensure that measurements are made at the appropriate time of year, but not all variations are so
predictable.
At larger distances from roads meteorological factors can significantly affect the received noise
level. Figure 6.1 illustrates this effect, showing the L A10,1hr noise levels measured
simultaneously at locations 10m and 500m from a busy motorway over a total of 30 days. Close
to the motorway the daytime noise levels differ by only about 3dB(A), whilst at 500m from the
motorway the potential variation in noise levels from day to day is up to 15dB(A). To account
for this variability consideration must be given to meteorological conditions, particularly vector
wind speed, when measurements are taken.

Figure 6.1: Variation in L A10,1hr sound pressure levels measured simultaneously at 10m and
500m from a busy motorway over 30 separate 24 hour periods. The component of vector
wind speed blowing from the road to the measurement location over the period ranged from
–4ms –1 to +4ms –1.
6.2.9 Effect of microphone location relative to reflective surfaces
The physical location of the measurement microphone relative to a solid vertical surface can
affect the measured noise level. In this context a clear distinction is made between ”free–field”
and ”façade” noise levels. Measurements taken ten metres or more away from a building façade
are termed “free–field” measurements whilst measurements taken one metre or less from a
building façade are termed ”façade” measurements. The effect of the traffic noise reflecting off
a façade under the latter condition results in an increase in the noise level of approximately
+2.5dB(A) at one metre from the façade compared with the level that would have been
measured in the absence of the façade.
154

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

The effect of microphone height on the measured noise level is not so straightforward, as two
different effects occur. These effects are both frequency dependent, one being due to ground
absorption and the other being due to ground reflections, the latter of which can both amplify
and attenuate noise through destructive interference. Two standard measurement heights are
employed: 1.2m to 1.5m to represent ground floor level and 4.0m to represent first floor level.
There are no simple relationships between the noise levels measured at the two measurement
heights, particularly at locations close to the road, and so the best advice is to be consistent and
compare like with like.

6.3 Calculation of road traffic noise and its radiation to
the environment
6.3.1

Calculation of environmental road traffic noise
The standard means of calculating road traffic noise for assessing the impact of roads is
contained in the DoT publication The Calculation of Road Traffic Noise (CRTN) (Department of
Transport, 1988).
The calculation of the traffic noise level is separated into two components. First, the effective
level of the traffic noise “at source” is estimated, then the effects of propagation as this noise
propagates away from the source to a more distant location are accounted for.
For any given location affected by noise from road traffic the received noise will comprise the
sum total of contributions from numerous individual vehicles. Whilst type approval tests for
noise emissions provide a valuable means of allowing the noise output of different types of
vehicle to be directly compared under carefully controlled test conditions, vehicles in everyday
use are subject to a multitude of variables that can affect their noise output significantly. These
variables include, amongst others, the speed of the vehicle, the engine type, the profile and
state of wear of the tyres and the type and state of road surface. The CRTN procedure recognises
this fact and chooses to establish a “typical” traffic noise level based on the average noise
outputs of light and heavy vehicles. To derive the source noise level in this manner, the CRTN
requires some basic input parameters:
❍
❍
❍
❍
❍

traffic volume flowrate (vehicles per hour or vehicles per 18 hour day);
mean traffic speed;
percentage of heavy goods vehicles;
road gradient, and
road surface type.

To ensure the validity of the calculation procedure, enough vehicles must use the road to
produce a relatively steady noise level. A minimum traffic volume flowrate of 200 vehicles per
hour or 4000 vehicles per 18 hour day is therefore stipulated, with correction factors
additionally being provided to extend the calculation down to 50 vehicles per hour or 1000
vehicles per 18 hour day. Based on these traffic flow limitations, one situation, for example,
clearly not covered by the CTRN method is that of intermittent night time lorry deliveries to
community stores in residential areas. The procedure set out in BS4142 (1997) is often resorted
to for the assessment of this type of noise, but the results of this level of increase over
background noise assessment should be used with extreme care.
Table 6.4 presents typical source noise levels calculated using the CRTN procedure. A base case
is taken as the noise level ten metres from the edge of the nearside carriageway of a five percent
gradient, impervious bitumen surfaced road carrying 20,000 vehicles per 18 hour day, of which
ten percent are HGV’s, with a mean traffic speed of 70km/hr. The calculated noise level for
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

155

these conditions is 74.3dB(A). The table lists changes in noise levels resulting from independent
changes in the various parameters, all other values remaining unchanged.
Parameter

Lower
parameter values

Base parameter values

Upper parameter
values

Vehicles/18hr day
Mean traffic
speed, km/h
%’age HGV
Road gradient

40,000
50km/hr

–3.0dB(A)
–1.6dB(A)

80,000
70km/hr

0.0dB(A)
0.0dB(A)

120,000
90km/hr

+1.8dB(A)
+1.7dB(A)

0%
0%

–2.0dB(A)
–1.1dB(A)

10%
5%

0.0dB(A)
0.0dB(A)

20%
10%

+1.4dB(A)
+1.0dB(A)

Table 6.4: Sensitivity of the traffic source noise levels calculated using the CRTN procedure to
changes in the basic input parameters.
The actual noise level heard by a listener will only match the source level calculated according
to the CRTN if that listener is located ten metres from the road in question. The CRTN procedure
therefore provides a means of extending the calculation to a receiver location at distances up to
300m from the road. The parameters included in this calculation comprise:
❍
❍
❍
❍
❍

distance between receiver and road;
acoustic screening between receiver and road;
ground cover between receiver and road;
reflections from solid objects such as buildings, and
layout of the road scheme relative to the receiver.

When the receiver location lies close to the road in question, the received noise level will be
dominated by noise emanating from the short section of the road immediately adjacent. In this
case, a single set of source and propagation parameters may be applicable. However, as the
receiver location gets further away from the road, the noise level may become affected by
several different segments of the road over which the basic parameters vary. As an example, a
stretch of road may contain a straight segment over which vehicles travel at 90km/h, yet this
may lead directly into a roundabout where the average vehicle speed reduces to 20km/hr with
a consequent reduction in traffic noise level. Equally, a continuous stretch of road may have a
noise barrier erected along part of its length, again significantly affecting the noise at the
receiver. One of the basic principles set out in the CRTN is therefore to break complex road
schemes into segments such that the level over any segment does not vary by more than 2dB(A).
The total noise level at the assessment point is then calculated by logarithmically summing the
contributions from the individual road segments.
Meteorological effects are known to significantly alter noise propagation outdoors, especially at
large distances between the source and receiver (see Figure 6.1). The CRTN procedure accounts
for this by stating that calculated traffic noise levels relate to “moderately adverse” conditions,
meaning that a light component of wind blows from the road towards the assessment point.
The sensitivity of traffic noise levels to meteorological conditions at large distances from roads
is recognised in the scope of applicability of the CRTN procedure with a suggested maximum
road to receiver separation distance of 300m. The current advisory document relating to the
design of roads, the Design Manual for Roads & Bridges (Department of Transport, 1994),
recommends the use of a Supplementary Report issued by the Transport and Road Research
Laboratory entitled Rural Traffic Noise Prediction – An Approximation (Transport and Road
Research Laboratory, 1978) to calculate traffic noise levels at larger distances from roads.
However, the methods presented in the TRRL report apply to broad brush calculations of noise
levels over large areas of land. For calculations of noise levels at specific locations for the
156

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

purpose of “before” and “after” comparisons it is recommended that the CRTN method always
be used, even for situations where the calculation point lies greater than the 300m from the road
in question.

6.4 Human response to noise
Levels of traffic noise up to one kilometre from a busy road are normally in the range 40dB
L Aeq,16hr to 75dB L Aeq,16hr . Noise at this level may affect different individuals in many different
ways, but it is effects such as long–term annoyance, interference with various activities and
possible health side effects through, for example, sleep disturbance or increased stress, that
form the basis for assessing the acceptability of this noise.
Human response to traffic noise is an important consideration where the noise is a perceived
problem, provided it can be demonstrated that noise control action can have a material affect.
The obvious response amongst a community is to welcome any measure designed to reduce
road traffic noise. However, noise control actions can carry non–acoustic consequences and
these factors can dominate the overall response. An example is the compromise between the
personal desire for private vehicle ownership set against the inconvenience of restricting
vehicular access to city centres.

6.4.1 Noise and activity interference
Noise can directly interfere with speech communications and can therefore have disruptive
effects in home, work and leisure environments alike. However, effective outdoor to indoor
attenuation can successfully mitigate this type of interference in most situations. For example,
even in the rare situations where outdoor noise exposure exceeds 75dB L Aeq,16hr,
high–performance acoustic double glazing or secondary glazing can attenuate sound levels
down to around 40dB L Aeq,16hr, provided, of course, that the glazing remains shut. At an
intrusion level of 40dB L Aeq direct interference with speech is likely to be minimal. Average
speech levels at a distance of one metre from the mouth range from 60dB(A) to 65dBA, which
exceeds the 40dB LAeq masking noise by a more than sufficient margin to avoid significant
interference. Outdoors, and in rooms where windows must remain open for ventilation purposes
or where the glazed area is large relative to the area of brick or blockwork, traffic external noise
levels of 75dB L Aeq are likely to result in considerable interference with speech
communications. This can prove a particular problem with schools and other institutional
buildings such as hospitals.

6.4.2 Noise annoyance
Noise annoyance describes the degree of unwantedness of a particular sound in a particular
situation. Human subjective response to traffic noise can vary from not being bothered at all,
through a state of becoming aware of the noise, right through to the point of becoming annoyed
by the noise when it reaches a sufficiently high level. This latter case represents the point at
which traffic noise may become a nuisance.
There is no statutory definition of noise annoyance, and this can lead to confusion. Numerous
noise annoyance surveys carried out over the last three decades have attempted to establish
engineering relationships between the amount of noise measured objectively using sound level
meters and the amount of community annoyance determined from questionnaires. A general
observation has been that annoyance increases with noise level, but attempts to find a common
relationship across all noise sources and listening situations have generally foundered. This task
has been complicated by the great range of individual sensitivities to noise observed in the
surveys.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

157

The results of three studies on subjective response are reported in the DMRB (Department of
Transport, 1994) which considers two different situations. The first concerns response to a
steady level of traffic noise with no sudden changes in level. The second case relates to a
sudden change in noise level, such as may occur when a new or modified road scheme is
developed. In the reported surveys the subjective effect of traffic noise was assessed by recourse
to questionnaires that enquired as to whether the reaction of the respondents to the noise was
to be bothered “very much”, “quite a lot”, “not very” or “not at all”.
The results of the research are summarised in Figure 2 of the DMRB. They demonstrate that a
free field external L A10,18hr traffic noise level of 55dB(A) results in eight percent of people being
“very much” or “quite a lot” bothered by the noise. At noise levels above 60dB(A) the
percentage of people annoyed “very much” or “quite a lot” increases at an average of around
2.5% for each 1dB(A) increase in noise level until at levels above 75dB(A) most people are
likely to be bothered by the noise to a significant degree. The region between 55dB(A) and
60dB(A) forms a transition area. For noise levels below 55dB(A) the correlation between noise
level and annoyance is not so clear, the observation being that community dissatisfaction
becomes more dependent on factors other than traffic flow.
The free field external L A10,18hr traffic noise level of around 55dB(A) at which there appears to
be a low degree of nuisance can be compared with other published data on what constitutes a
generally acceptable level of environmental noise. The UK Planning Policy Guidance Note
(PPG) PPG 24 (Department of the Environment, 1994a), the World Health Organisation
Environmental Health Criteria Document 12 on Noise (World Health Organisation, 1980), the
CEC, ”Environment and Quality of Life, Damage and Annoyance Caused by Noise”
(Commission of the European Communities, 1975) and the Organisation for Economic
Co–operation and Development (OECD) “Reducing Noise Impact in OECD Countries”
(Organisation of Economic Co–operation and Development, 1991) all conclude that daytime
L Aeq environmental noise levels of less than 55dB will result in little likelihood of community
reaction. The daytime averaged L A10,T noise level is typically 2dB(A) higher than the daytime
averaged L Aeq,T noise level in environments where road traffic noise dominates.

6.4.3 Noise and sleep disturbance
Sleep disturbance can vary depending on circumstance. Measurable reflex responses have been
observed at sound levels down to around 45dB to 55dB LAmax indoors. The latest revision of
the 1980 World Health Organisation Environmental Health Criteria Document 12 on Noise
(World Health Organisation, 1980) recommends guideline values of 30dB L Aeq and 45dB L Amax
indoors to avoid negative effects on sleep. However, there is no real evidence that any such
reflex responses at low sound levels are anything other than normal adaptations by the body to
changes in the external environment. There is also considerable evidence that people can
habituate to much higher levels of environmental and transportation noise without awakening
taking place (Commission of the European Communities, 1996).

6.4.4 Noise and non–auditory health
Increasing public concern is being voiced that sustained or repeated exposure to noise may lead
indirectly to adverse health effects. However, there is no clear mechanism by which the
observable and quite natural short–term physiological responses to noise might translate into
damage to the body’s physiology. No firm proof therefore currently exists as to the presence of
such non–auditory health effects.

6.4.5 Noise and community response
The Wilson Committee on the “Problem of Noise” was appointed in April 1960 to “examine the
nature, sources and effects of the problem of noise and to advise what further measures can be
158

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

taken to mitigate it”. The final report (Wilson, 1963) noted “there is a considerable amount of
evidence that, as living standards rise, people are less inclined to tolerate noise”.
The World Health Organisation published in 1980 the WHO Environmental Health Criteria
Report 12 on Noise (World Health Organisation, 1980). Road traffic noise was singled out as the
main source of community noise and the possible adverse health effects of noise were noted.
Thus the possibility of the adverse secondary health effects of noise was increasingly introduced
in addition to annoyance affects.
The community noise problem is fundamentally a matter of public perception. Since the Wilson
report considerable improvements have been made in quietening the engine and exhaust noise
from individual road vehicles. Acting against this reduction is the volume of traffic, people’s
expectations for peace and quiet and a general increase in public environmental awareness.

6.5 Planning Issues
6.5.1 Policy background
It is the duty of planning authorities to use the best available advice to avoid environmental
noise problems. This is particularly true of road traffic noise because, once introduced, it is
often difficult to ameliorate.
Road traffic generates environmental noise, and environmental noise is almost always viewed
as being undesirable. However, roads can also bring significant benefits to an area, including
easier communications and the indirect generation of income through increased opportunities
for residential and business expansion and tourism. As part of the planning process, these
benefits must be weighed up against any adverse environmental impact. This section presents
an overview of the various requirements, both statutory and in the form of Government advice,
general advisory guidelines and research produced by others, that should be accounted for in
this process.
Planning Policy Guidance Note PPG 1, General Policy and Principles (Department of the
Environment, 1994b) makes clear the intention to work towards sustainable development and
growth. This aim requires that decisions in the planning field do not deny future generations the
best of today’s environment but also do not unduly restrict development. The importance of
Development Plans is stressed, the purpose of which is to set out general development policies
within specific areas. These policies should include the identification of areas suitable for both
noise sensitive and noisy development. To identify land use areas based on their noise
environments the advice contained in PPG 24 Planning and Noise should be followed
(Department of the Environment, 1994a). This general advice is reiterated, specifically for
highways development, in PPG 13, Transport (Department of the Environment, 1994c) which
states that “great care must be taken to minimise the impact of any new transport infrastructure
projects, or improvements to existing infrastructure, on both the natural and built environment”.

6.5.2 Planning Policy Guidance Note PPG24 – Planning and Noise
PPG 24 advises on the role of the planning system to minimise the adverse impact of noise. Two
aspects of the control of road traffic noise at the planning stage are addressed.
The first case relates to the development of noise sensitive accommodation near an existing road
scheme. The measured or calculated existing noise levels are categorised into Noise Exposure
Categories (NEC’s). The noise impact on the proposed development is then assessed according
to which category the noise environment falls within. In all cases the existing noise environment
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

159

is defined in terms of both the “daytime” L Aeq,16hr measured over the period 07:00 to 23:00 and
the “night–time” L Aeq,8hr measured over the period 23:00 to 07:00. All noise levels given in PPG
24 are stated as “free field” noise levels. That is, the noise levels measured out of doors at the
proposed location of the noise sensitive development. The notes relating to each of the four
NEC’s are:
❍ NEC “A” – Noise need not be considered as a determining factor in granting planning
permission.
❍ NEC ”B” – Noise should be taken into account and, where appropriate, conditions
imposed.
❍ NEC ”C” – Planning permission should not normally be granted unless other reasons
dominate.
❍ NEC ”D” – Planning permission should normally be refused.
The noise levels associated with the upper limit of NEC “A” for road traffic noise are 55dB(A)
daytime and 45dB(A) night–time. These noise levels have been selected on the basis of guidance
provided by the World Health Organisation (World Health Organisation, 1980).
The second case relates to situations where a new road scheme is proposed near an existing
noise sensitive development. In this instance PPG 24 refers to European Commission Directive
85/337/EEC (subsequently updated by Directive 97/11/EC) (European Commission, 1985, 1997)
which, through section 105A of the Highways Act, requires that an environmental assessment,
including the effects of noise, be undertaken in respect of road improvements likely to have
significant environmental impact. Environmental assessment is also required for all projects
listed under Schedule 2 of the Town and Country Planning (Assessment of Environmental Effects)
(England and Wales) Regulations 1999 if the proposed development is likely to have significant
environmental impact. This environmental statement should be made available for public
scrutiny alongside a statement of the economic and other benefits of the proposal.
Unlike the case of noise sensitive development in an existing noisy area, PPG 24 does not
propose noise levels that are deemed acceptable for new roads affecting existing noise sensitive
areas. This is primarily because of the reduced opportunity for noise mitigation measures on
existing houses. Instead PPG 24 refers to the Noise Insulation Regulations 1975 (Department of
the Environment, 1975) and the Noise Insulation Amendment Regulations 1988 (Department of
the Environment, 1988) and also to the DMRB, Volume 11, Section 3, Part 7, “Traffic Noise and
Vibration” (Department of Transport, 1994). Reference is also made to the Road Traffic
Regulation Act 1984, which could be used by highways authorities to manage traffic to reduce
the impact of noise, and to BS5228 (1984), parts 1–4. “Noise Control on Construction and Open
Sites”, which may apply during the construction of roads.
PPG 24 also presents an overview of possible measures to mitigate noise. The proposed methods
are generally equally applicable to road traffic noise as to other noise sources. It is suggested
that noise control measures should be proportionate and reasonable and include one or more
of the following techniques:
❍ Engineering, which includes reduction of the noise “at source”.
❍ Lay–out, which includes separating the noise sensitive development as far as possible
from the noise source, or introducing non–noise sensitive development between the road
and the noise sensitive development.
❍ Administrative, which includes restrictions on the use of a road, maybe by controlling
vehicle type, total vehicle numbers or vehicle speed.

160

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

6.5.3 Land Compensation Act 1973
Part 1 of the Land Compensation Act 1973 provides a compensation mechanism for owners of
properties due to any of five physical factors resulting from the creation or the use of a piece of
infrastructure. This includes noise from new or altered road schemes.
The Act does not seek to compensate homeowners for loss of amenity caused by any increase
in noise levels. Its sole purpose is to compensate for any reduction in the value of the property
on the open market. The reduction in value can relate to factors other than noise. Also, different
levels of noise may have a greater or lesser impact on the value of the property depending on
the location and type of property. It is therefore not possible to set a noise limit at which
compensation becomes payable. Instead a valuation is undertaken by a surveyor who must take
account of all relevant factors. The duty of the surveyor is to determine the likely view of a
“typical” prospective purchaser.
The ultimate question in Land Compensation Act claims is whether this purchaser would offer less
money for the property than had the new level of traffic noise not been present, given that the
purchaser would typically not have the benefit of a “before” and “after” comparison. Compensation
claims can only be made from one year after the opening of the road scheme, by which time the
effects of noise on the property can be established by measurement. However, there is no
requirement to undertake formal noise measurements in support of claims for compensation. Costs
of compensation claims should never be underestimated. In the case of at least one new road
scheme in England the cost of Part 1 claims exceeded the construction costs of the road itself,
although the use of quieter road surfaces should mean this eventuality would not occur again.
In cases where the traffic noise levels are sufficiently high, Section 20 of the Land Compensation
Act introduces an additional mechanism for providing physical measures to reduce noise in
homes. This mechanism is covered by the Noise Insulation Regulations.

6.5.4 Noise Insulation Regulations 1975
The Noise Insulation Regulations are secondary legislation enacting the provisions of Section 20
of the Land Compensation Act. The Noise Insulation Regulations 1975 (Department of the
Environment, 1975) and the Noise Insulation Amendments Regulations 1988 (Department of the
Environment, 1988) both relate to the protection of residents inside their homes against
significant levels of traffic noise. The Regulations set a fixed limit for external traffic noise,
combined with a minimum increase in noise level, above which the responsible authority must
provide noise insulation schemes under Regulation 3. The aim is to enable the affected residents
to benefit from a reduction in the noise level inside their homes. Eligible rooms are noise
sensitive living rooms and bedrooms in dwellings and other residential properties lying within
300m of the proposed road scheme if it is calculated that within 15 years from the opening of
the new or altered road:
❍ the traffic noise level at one or more façades will increase by at least 1dB(A) and will not
be less than 68dB(A) L A10,18hr ; and
❍ noise caused or expected to be caused by traffic using the new or altered section of road
will contribute at least 1dB(A) to the overall noise level.
In addition to the mandatory provision of Regulation 3, Regulation 4 provides an extra
discretionary power in the case of alterations to an existing road, in which case the 1dB(A)
increase rule does not necessarily have to be satisfied.
The Noise Insulation Regulations are therefore quite specific in determining whether or not a
claim property is eligible for a sound insulation grant. This is both in terms of the proximity of
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

161

the claim property to the road scheme and also in terms of the absolute traffic noise level
experienced at the claim property. Calculations for eligibility are carried out using the
Calculation of Road Traffic Noise (Department of Transport, 1988) so that eligible properties can
be identified and insulation installed prior to the opening of the road and, for the purpose of
Regulation 8, prior to construction of the new road.

6.5.5 Sound insulation and noise reduction for noise sensitive buildings
Where insulation of buildings is necessary, or where the sound insulating properties of an
existing building construction are required, then BS 8233 (1987), provides sample acoustic
performances for a number of typically encountered constructions, together with recommended
internal noise levels for various noise sensitive developments such as homes, hospitals, nursing
homes and schools. Specialist advice for school and hospital buildings is provided in
Department for Education Design Note 17: Guidelines for Environmental Design in Educational
Buildings and Hospital Technical Memorandum 45.

6.5.6 DoT Technical Memorandum – Calculation of Road Traffic Noise
The Department of Transport publication Calculation of Road Traffic Noise (Department of
Transport, 1988) provides a well–defined procedure for both calculating and measuring traffic
noise levels. It has already been covered in some detail in Section 6.3 of this chapter. The
procedures set out in the CRTN document must be adopted to assess eligibility for grants under
the Noise Insulation Regulations, for which its applicability is formally limited to the range of
conditions covered by the Noise Insulation Regulations of up to 300m from the road. The
calculation method is also used for more distant calculations of traffic noise, for example for use
in environmental impact assessments, although less reliance can be placed on the calculated
noise levels as road to receiver separation distances increase above 300m.

6.5.7 Design Manual for Roads and Bridges, Vol 11, Sec 3, Pt 7, Traffic Noise and
Vibration
The Department of Transport publication the Design Manual for Roads and Bridges , Volume 11,
Section 3, Part 7, “Traffic Noise and Vibration” (Department of Transport, 1994), offers perhaps
the most comprehensive and up to date formally published Government advice on noise issues
associated with road developments. The document, along with the Calculation of Road Traffic
Noise, is referenced in paragraph 1 of Annex 3 of PPG 24 under the heading “detailed guidance
on the assessment of noise from different sources: noise from road traffic”.
The traffic noise and vibration section of the DMRB is itself divided into a number of chapters.
Chapter 2 provides an overview of traffic noise in general. Chapter 3 addresses subjective
response to road traffic noise. Chapter 4 is primarily intended to assist in the assessment of the
impact of noise on people already living in an area when a change in noise level occurs. For
instance, it details the objectives of any noise assessment as being to establish the magnitude
and significance of noise changes. Chapter 5 addresses the issues of measuring and predicting
traffic noise levels and assessing noise nuisance.

162

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

6.6 Guidance on best practice and noise mitigation
measures
6.6.1 Land use and planning
The single most effective means of reducing people’s exposure to road traffic noise is to use the
planning system. PPG 13 “Transport” stresses the need to take great care to minimise the impact
of any new transport infrastructure on both the natural and built environment, stating that new
routes should make best possible use of existing landscape features to reduce noise, where
necessary providing additional screening through earth mounds. These general aims are
reiterated in PPG 24 Planning and Noise where the need to prevent the development of new
roads near existing noise sensitive developments, and likewise the need to prevent the
development of new noise sensitive development near existing roads, is stressed.
Ideally, noise sensitive and noise insensitive areas should be identified in Local or District Plans.
Noise sensitive areas should be designated for the building of houses, schools, hospitals and other
similarly sensitive developments. These noise sensitive areas should be located away from existing
major roads, and major new road development should also be excluded from such areas, although
to be functional it would be unreasonable to expect the exclusion of all vehicles. In contrast, noise
insensitive areas should be designated for the building of factories, warehousing and other similar
developments. These areas could be located close to existing major roads and the planning system
should allow the development of major new road schemes along such corridors. Noise insensitive
developments such as factories and warehousing can often derive direct benefit from close
proximity to major traffic routes through better accessibility.
PPG 24 takes a pragmatic view in allowing authorities to make choices when faced with
conflicting requirements between acoustic ideals and other considerations. One such factor is
current policy to encourage the redevelopment of brownfield sites. Consequently many such areas
have been allocated for residential development in Local and District Plans, and these areas are
often subject to existing road traffic noise levels higher than those at the upper limit of the lowest
NEC “A” band of PPG 24. Where possible it is desirable to plan noise insensitive developments,
such as warehousing or offices, as a buffer zone between the road and the noise sensitive
development, but this is not always an acceptable solution if the land has been designated entirely
for residential use. This means that one or more of the noise control measures discussed below
will be necessary to provide what is considered an acceptable acoustic environment.
Likewise, whenever a new road is planned its route should be optimised to achieve the best
compromise between cost and environmental disruption of all types, not just noise. As part of
this process of assessment it may be concluded that factors other than noise have an overriding
precedence, and the new road is so important as to merit increasing noise levels at existing
houses to what might, in other circumstances, be considered unacceptable. Once again in this
instance one or more of the following noise control measures will be required to reduce the
noise levels at the existing noise sensitive dwellings to acceptable limits. The first three of these
measures are perhaps of most interest here as they can generally be applied retrospectively to
existing roads to reduce environmental noise levels.

6.6.2 Road surfaces
Tyre noise results from the interaction of the tyre with the road surface, and so it is an
interaction of the properties of both the tyre and road surface that control noise generation.
Treatments to the vehicle itself are outside the scope of this document, so the noise control
solution available to the highway engineer to reduce tyre noise is limited to the use of quieter
road surfaces. However, it must not be forgotten that the development of quieter road surfaces
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

163

needs to be constrained by the overriding requirement to provide skidding resistance and
effective surface water run off. Approval of new road surfaces is achieved through the Highways
Authorities Product Approval Scheme (HAPAS).
Much useful data on quiet road surfaces has been collated for two recent review articles
(Wright, 1999; Nelson and Phillips, 1997). This section provides an overview of that data,
including a comparison of the acoustic benefits of the newly developed quiet road surfaces with
traditional hot rolled asphalt and transversely textured concrete road surfaces.
Porous quiet road surfaces
Initial efforts to produce quieter road surfaces concentrated on the use of porous asphalt. This
surface technology offers a “negative” texture, leaving the running surface flat. The positive
benefits are reduced tyre noise as well as reduced spray and reflected headlight glare in wet
conditions. Porous asphalt was adopted on a number of road schemes in the early 1990’s.
Results of early trials indicated reductions of 5dB(A) or more whilst still providing adequate
skidding resistance in wet conditions. Despite these early findings, the CRTN method
incorporated a more cautious 3dB(A) reduction when comparing porous asphalt with traditional
hot rolled asphalt due to the potential for a reduction in acoustic performance over the 15 year
prediction period defined in CRTN.
Porous asphalt is more expensive to install, being much thicker than hot rolled asphalt surfaces
at between 50mm and 100mm overall. It is less durable, incurs higher maintenance costs, and
contains no recycled material, again leading to increased cost as well as environmental
implications. Porous asphalt can also prove difficult to keep free of ice in winter and it becomes
acoustically less effective as the pores clog with use.
Non–porous quiet road surfaces
Given the shortcomings of porous asphalt, recent research efforts have concentrated on
understanding noise generation mechanisms at the tyre/road interface with a view to producing
harder wearing road surfaces that are randomly textured with a given texture depth, rather than
relying on the porosity of the surface (Nelson and Phillips, 1997). This research has identified
the possible use of either exposed aggregate concrete or dense thin surfacings as possible
solutions. Both of these produce a non–porous layer with the desired relatively high friction and
randomly textured surface. The common characteristic among all quieter surfaces is their
“negative texture”. That is, the surface on which the tyres roll is relatively flat and the spaces
between the surface aggregate chippings provide the necessary macrotexture allowing water
and air to escape from under the tyre. Several proprietary low–noise road surfaces are now
available in the UK, largely based on development work undertaken in Europe (Wright, 1999),
although the texture depth has generally had to be increased in order to meet UK requirements
for wet skidding resistance.
Current non–porous quiet surfaces include Exposed Aggregate Concrete (EAC) and thin layer
surfaces such as Stone Mastic Asphalt (SMA), Ultra Thin Hot Mix Asphalt Layer (UTHMAL), Thin
Polymer–Modified Asphalt Concrete (VTSL), Hybrid UTHMAL–VTSL, and Multi–Layer Surface
Dressings (MLSD). Detailed discussion of the non–acoustic properties of these technologies is
beyond the scope of this document. An overview of the construction techniques involved is
contained in Nelson and Phillips (1997), and reference should also be made to HD36 and HD37
of Volume 7 of the DMRB.
Exposed aggregate concrete involves spraying a retarding agent on the freshly laid concrete.
This slows the curing of the surface layer relative to the underlying concrete. After around 20
hours, the soft surface cement is removed with a wire brush to expose the randomly distributed
164

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

aggregate. Thin surfacings are manufactured by pre–mixing chippings with the binder before
laying, with no additional chippings being rolled into the surface after laying. The properties of
the aggregate (10mm to 14mm) coupled with the thinness of the layer (15mm to 30mm) means
the surface is easily compacted. It also means the surface is ideal for resurfacing existing roads
as it offers speed and cost advantages. Initial evidence also indicates that thin surfacings can be
as durable as hot rolled asphalt.
Direct comparisons of the relative levels of traffic noise from vehicles using the various road
surfaces are hampered because standard measurement procedures have not been used across all
tests. Wright (1999) reveals variations of up to plus or minus 2dB(A) between results for different
proprietary materials using the same technology. Accepting these limitations, Figure 6.2 presents
typical differences in the measured “A”–weighted sound pressure levels between the various quiet
road surfaces. All results are expressed relative to hot rolled asphalt for both light vehicles and
heavy goods vehicles travelling at 90km/hr. This situation will hopefully soon change, with all
materials supplied to the Highways Agency as surfacing products requiring properly authenticated
results measured in accordance with a standard HAPAS defined test procedure.
The collated test data indicates that porous asphalt still gives the highest reductions in overall
noise levels, but capital and maintenance costs preclude its use as a viable treatment in most
instances. Stone mastic asphalt gives the best overall results of the thin surface treatments, both
in terms of its combined light vehicle and HGV performance and in terms of the range of
audible frequencies over which it offers benefit. Some hybrid surfaces have demonstrated
potential reductions in excess of those achieved by stone mastic asphalt, but the test data is
limited. The lack of consistent test data, coupled with the fact this is still a developing area of
technology, mean that more rigorous comparative testing is required before definitive advice
can be provided on the preferred thin surface treatment to be used in any given situation.

Figure 6.2: Typical reductions in overall dB(A) noise levels expected using different road
surfaces. All results are expressed relative to the noise level produced on hot rolled asphalt.
Reductions are shown for both light vehicles and heavy goods vehicles travelling at a nominal
speed of around 90km/hr. Differences in measurement procedures mean the spread on the
data for each type of surface may be up to 2dB(A) either side of the levels shown.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

165

6.6.3 Noise barriers and landscaping
As was the case with the discussion on quiet road surfaces, this section can only offer a brief
overview of noise barrier technology. For a thorough discussion of the topic the reader is
referred to the recently published book Environmental Noise Barriers (Kotzen and English,
1999). This publication has been used as a reference for much of the information presented
here. The reader is also referred to Volume 10 Section 5 of the DMRB and in particular HA
65/94 and HA 66/95.
The construction of a well–designed noise barrier along the side of a road can reduce noise levels
by as much as 15dB(A), provided the affected properties are located within 150m or so of the
barrier. The overall effectiveness of a barrier depends primarily on the increased path length
between the source and receiver as a result of the sound having to diffract over the top of the
barrier instead of travelling via a direct line of sight between the traffic noise source and the
receiver. Thus the higher the barrier, and the closer it is to either the source or the receiver, the
greater the additional attenuation achieved. The potential noise reductions offered by noise barriers
for closely located properties are therefore much larger than the approximate 6dB(A) offered by
even the most effective quiet road surface. The attraction of a quiet road surface is that its effect in
reducing traffic noise levels is experienced equally at all distances from the treated road.
The requirements to maximise the acoustic effectiveness of noise barriers can conflict with the
desire to minimise the visual impact of such barriers, especially where barriers comprise simple
concrete or heavyweight timber fences as is usually the case alongside roads in the UK.
However, considerably greater ingenuity is shown in both the acoustic and aesthetic design of
roadside noise barriers throughout the rest of Europe. This is often driven by a general target for
environmental daytime noise levels of around 55dB L Aeq to 65dB L Aeq in many European
countries, as opposed to the target of 68dB L A10 often aimed for in the UK as a result of the
Noise Insulation Regulations. The more advanced barriers found in Europe are undoubtedly
more costly, but the improvement in the acoustic and visual environment they provide around
major roads is considered by many to justify the extra cost. Some of this additional cost may, in
any case, be offset in the UK against a reduction in the value of claims under the Land
Compensation Act.
Once it has been established that a noise barrier will provide the necessary reduction in traffic
noise around a road scheme, the following considerations should be taken into account when
selecting and siting the barrier.
Barrier size and placement
The most commonly used theory for noise barrier performance is that given by Maekawa (1968).
This theory calculates the performance of a noise barrier as a function of the path length
difference and the wavelength of the sound being considered. The larger the path length
difference, or the smaller the wavelength of the noise (which implies the higher the frequency
content of the noise) the larger the barrier effect. CRTN adopts a simplified approach based on
the effect at 1kHz as being representative of the performance of a barrier over the dominant
range of traffic noise frequencies.
A noise barrier should therefore be sized and located such that it maximises the acoustic path
length difference between the source and receiver compared with the direct acoustic path in the
absence of the barrier. Theory shows that for a typical traffic noise spectrum and a path length
difference of one metre a reduction of 15dB(A) may be achieved. Reducing the path length
difference to 0.2m results in a theoretical reduction of 10dB(A), and a path length difference of
0.0m gives a theoretical reduction of 5dB(A). These reductions assume neutral atmospheric
conditions. Under conditions of downwind propagation or temperature inversions the
166

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

performance of acoustic barriers may be significantly reduced. Any barrier will give its
maximum acoustic performance if located as close as possible to either the source or the
receiver as this will maximise the path length difference. In practice, it is more usual to locate
roadside noise barriers closest to the roadside rather than close to the receiver. Where roads are
in cuttings the barrier is most effective if placed at the top of the cutting slope rather than
adjacent to the road. Again, this is to maximise the path length difference.
Because the path length difference is the main parameter controlling barrier performance, it is
often traffic on the far carriageway that dominates the noise levels at acoustically screened
locations. If this is the case then useful additional attenuation may be achieved by placing a
second barrier along the central reservation to more effectively screen the far carriageway.
Remembering that noise can diffract around the edges of a barrier exactly the same as it diffracts
over the top, the length as well as the height of the barrier must be appropriately specified. A
barrier covering an angle of 160 degrees subtended from the receiver to the road will generally
ensure that end diffracted rays are not significant. Angling the ends away from the road (Kotzen
and English, 1999) can reduce the length of a barrier required to achieve this.
Sound insulation performance of the barrier material
Given the practical limit of attenuation of a roadside barrier of around 15dB(A) the constructional
requirements for barriers themselves are not onerous. The principal requirements are that the
barriers should have no air paths through them and that they should provide a sound reduction
performance in the absence of any airborne paths around the edges of the barrier at least 10dB
higher than the target performance of the installed barrier. The Department of Transport
document Noise Barriers – Standards and Materials (Department of Transport, 1976), now
superseded by HA 66/95 in DMRB Volume 10, Section 5, gives a simple formula for calculating
the minimum surface mass required of a barrier to achieve this. A standard test procedure, EN
1793 (European Committee for Standardisation, 1997) has been adopted for measuring the
performance of noise barriers. However, this is a laboratory–based test for measuring sound
absorption and sound insulation properties of the barrier material itself. A field measurement
technique for quantifying noise barrier performance is currently under development.
Effects of reflections from hard surfaced barriers
Where roadside barriers are installed on both sides of a road, and where the road facing
surfaces of the barriers are acoustically hard, traffic noise can reflect between the two barriers
without being absorbed. This noise can then diffract over the barriers to escape to the
environment. Watts (1995) has demonstrated that even for two metre high barriers located 34m
apart the reduction in barrier performance can be as much as 4dB(A). A similar situation can
result between high–sided vehicles and an acoustically hard barrier. The effects of reflections
can potentially reduce the effectiveness of a barrier, although the magnitude of this effect
compared with the complicating effects of scattering caused by the mixed flow of road vehicles
is not at present fully quantified. Two effective solutions exist to remedy the problem of multiple
reflections between barriers or between high–sided vehicles and a barrier. These solutions
comprise either angling the barriers in towards the road or out from the road (an angle of as
little as 10° is all that is required) or applying an acoustically absorptive treatment to the side
of the barriers facing the road.
Diffraction effects over noise barriers
The installed performance of noise barriers is limited principally by diffraction of sound over the
top of the barrier. For this reason considerable research effort has been expended in developing
improved designs for detailing along the top edges of noise barriers to limit the diffraction of
noise over the top. The designs fall into two major categories.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

167

The first category involves a significant extension to the simple barrier to include a large
cantilevered top section tilted over the road. In extreme examples this cantilevered section
extends over the entire nearside carriageway to become a galleried barrier. These types of
barriers can be extremely effective in reducing sound diffraction over the top of the barrier. This
effectiveness is gained only through a significant cost penalty and through a significantly
increased visual impact. However, examples from Europe have demonstrated how the adverse
visual impact of even the largest cantilevered barriers can be minimised.
The second category of barriers are those that include smaller–scale edge details such as
T–shaped, multiple edges, Y–shapes, tubular cappings or phase interference devices (Kotzen
and English, 1999). Improvements in performance of between 1dB(A) and 3dB(A) have been
reported for such modifications, but the complexity and cost of manufacture of the barriers has
increased significantly. Also, one of the major problems of acoustic barriers is their generally
poor aesthetics, and attempts to improve the acoustic design in this manner can tend to detract
rather than add to the visual appeal of the barriers.
Earth bunds
The use of earth bunds as more aesthetically pleasing ‘natural’ acoustic barriers can be
considered particularly in rural areas where other types of barrier may be visually unacceptable.
Performance gains attributable to bunds are slightly less than that of acoustic barriers for the
same path length difference between source and receiver. The performance difference can be
minimised by making the bund flat topped rather than wedge shaped. The major disadvantage
of earth bunds is their width relative to their height, which necessarily often takes up land and
places the top of the bund further away from the source than may be desirable in terms of
optimising the acoustic performance.
Vegetative barriers
A possible compromise between acoustic barriers and earth bunds is the concept of a “living
wall”. This typically comprises an earth centre retained behind natural meshed panels with
willow or a similar plant growing from the central earth. These barriers can therefore look
reasonably natural when installed whilst taking up less area, and they again offer a similar
performance to purpose built acoustic barriers. However, long term monitoring of vegetated
barriers has indicated that the living systems do not last. They are also expensive to construct
and maintain because of the requirements for skilled manual labour. Without this maintenance,
living walls can become less natural looking over time.
Vegetation
The planting of a visual screen of trees or shrubs between traffic noise sources and noise
sensitive developments can result in a perceived improvement due to the removal of the visual
impact of the road. However, objective measurements have revealed that reductions in
measured traffic noise levels are typically limited to 1dB(A) for each five–metre depth of trees,
and only in the case of mature, well established vegetation. Attenuations of 6dB to 8dB have
been reported (Kragh, 1982) for frequencies below 250Hz and above 1kHz, but because traffic
noise is dominated by frequencies between these two limits such large attenuations are not
reflected in the overall reduction in traffic noise of around 3dB L Aeq . Quite apart from the
limited acoustic benefits to be gained, the use of vegetation as a noise barrier is not generally
recommended due to the length of time it takes to establish a dense belt of trees or bushes, and
the subsequent effort that may be required to maintain this vegetation.
Screening using intermediate less noise sensitive buildings
The possible introduction of non–noise sensitive buildings such as warehousing, offices or light
industrial units between the road and any noise sensitive developments has already been
168

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

proposed as an option for reducing exposure to traffic noise. This possibility should not be
overlooked as a practical alternative to building a noise barrier, provided the buffer zone
buildings can be constructed so as to have no gaps through them.

6.6.4 Traffic management
Urban traffic noise levels can be dramatically affected by traffic management schemes and
changes in driver behaviour. However, great care must be taken to ensure that traffic
management does actually achieve the desired aim of reducing noise and does not exacerbate
the problem.
Three important parameters interact as the dominant controlling factors with regard to road
traffic noise generation, and all of these parameters can be controlled by traffic management
schemes. These factors comprise the number of vehicles in a traffic stream, their speed and the
proportion of HGV’s. These parameters, together with the road gradient, interact to produce a
complex relationship with the radiated noise. The complexity of this relationship has already
been illustrated in Table 6.4.
For minimum noise output it is intuitive that the number of vehicles, and particularly HGV’s,
should be reduced along with the speed of the vehicles. However, a reduction in vehicle
numbers, especially HGV’s, on a busy road will under most circumstances result in an increase
in mean traffic speed. Therefore, any scheme designed to limit traffic congestion must also
carefully control traffic speed if it is to succeed at reducing overall noise levels. Table 6.3
illustrates this fact for a busy main road. A road carrying 80,000 vehicles per day at an average
traffic speed of 70km/hr can have the number of vehicles increased to 120,000 vehicles per day
with almost no change in overall noise level provided the mean traffic speed is simultaneously
limited to 50km/hr.
In urban situations it is often found that traffic noise is worse in the mid–morning and
mid–evening when traffic is fairly busy but free flowing, and not during peak rush hour periods
when traffic is often at a virtual stand still. A further complication arises in urban situations
where stop/start traffic management schemes are introduced through priority obstructions.
Whilst these schemes can have the desired effect of reducing mean traffic speed, they can result
in increased noise levels due to vehicles, and particularly HGV’s, being accelerated too hard as
they repeatedly pull away from the obstructions. The use of speed bumps, too, can introduce
their own noise problems as vehicles travel over them. Careful planning is required to place
obstructions as far as possible from noise sensitive dwellings, although as these schemes are
usually in densely built up residential areas this ideal is not always achievable. One other
possible means of reducing noise in residential areas is to introduce a lorry ban, where this ban
can either be total or timed to correspond with the more sensitive times of the day. Lorries still
contribute disproportionately to noise levels, being approximately rated as equivalent to five
cars.
Action plans to reduce traffic noise should always be considered in connection with air quality
planning issues, as the two requirements can work against each other: lower traffic speeds
generally produce less noise but also result in higher levels of air pollution.

6.6.5 Cuttings, tunnels and enclosures
The use of tunnels and enclosures can be employed very successfully to reduce road traffic
noise. This is because these methods can fully enclose the source of sound. However, the costs
of such treatments are usually prohibitive relative to the acoustic benefits and their use usually
must be justified on grounds additional to noise. Tunnels can, for instance, reduce the local
effects of road traffic on air pollution and dust.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

169

Cuttings can also be used to reduce noise, and reductions similar to those achieved using
roadside acoustic barriers can result. Caution is again advised against the potential build up of
reverberant noise between the sides of the cutting if these are vertical hard walls, or between
the side of high sided vehicles and the cutting wall. In such instances, sound can reflect back
and forth between the acoustically reflective surfaces, with little loss of acoustic energy, before
leaking out of the cutting to the environment. A possible solution to this is either to line the
cutting with acoustically absorptive side panels, or to install acoustically absorptive louvers
above the road along the top of the cutting.
Additional care should be taken to locate the ends of the tunnel away from noise sensitive
developments, as the impact of sudden changes in noise around these areas as vehicles enter
and exit the tunnel can be significant.

6.6.6 Building design and layout
The shielding of noise sensitive buildings by intervening noise insensitive buildings such as
quiet factories, warehouses or multi–storey car parks can enable the development of land right
up to busy roads. Where it is desired to build residential properties as close as possible to a road
with no buffer zone, the use of single aspect housing with the living room and bedroom
windows facing in the opposite direction to the road, or the use of patio–style housing, can also
be an effective design measure. These single aspect buildings can then act as noise barriers for
houses further in to the estate.
Where windows are installed in the noisy façade of a dwelling or other noise sensitive property
these should be treated proportionate to the external noise level. The sound insulation provided
by a building wall is strongly influenced by the area of window relative to the solid wall.
BS8233 (1987) provides information on target internal noise levels for noise sensitive
developments, along with typical sound insulation offered by various types of building
construction.
Even more significant than the area of glazing relative to the total façade area is the effect of
openings in the wall required for ventilation. In dwellings this ventilation is usually achieved
through the use of opening windows. If an external wall has an opening or gap of about one
percent of its area, the overall noise reduction achieved by the façade will be limited to around
20dB(A), even if the rest of the wall provides a high degree of insulation. If the opening is ten
percent, which is a not uncommon proportion for open windows, an overall noise reduction of
not more than 10dB(A) can be expected for the façade. With single glazed opening windows
tightly closed onto a good weather seal an overall noise reduction of around 35dB(A) may be
achieved. To achieve adequate protection against noise levels eligible under the Noise
Insulation Regulations it will generally be required to install sealed secondary glazing with a
minimum 100mm air gap behind the primary glazing. In all cases, it must be ensured that
adequate ventilation is provided to the rooms with windows sealed closed. The use of
“acoustic” trickle ventilators in higher noise environments usually results in an unacceptable
reduction in the overall acoustic performance of the façade. In such cases, either high
performance acoustic airbricks must be installed or, in extreme cases an attenuated forced
ventilation system will be required.
In schools and hospitals, noise insensitive areas such as gymnasia, dining halls, kitchens,
corridors and service areas can be used to shield more noise sensitive areas. Window treatment
such as the provision of double windows may be required, but alternative means of ventilation
and air conditioning may also be necessary, as discussed above for the case of residential
dwellings.
170

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

6.7 Principal recommendations
The level of attenuation that can be achieved using any of the methods covered in this chapter
is dependent on many factors such as traffic speed, proximity to housing, volume of traffic and
so on. The cost of the remedial measures can also vary significantly between different situations.
It is therefore difficult to select just one or two priority actions based on a cost–benefit type
analysis, and the final choice of noise reducing methods in any given situation must be
determined on a site by site basis.
❍ When planning a new road, or improvements to an existing road, investigate all potential
routes to minimise adverse environmental noise impact. Evaluate the impact of different
routes accounting for separation distances and natural screening effects between the road
and noise sensitive areas.
❍ Do not assess noise impact solely on the grounds of compensation costs based on the
68dB L A10 noise insulation criterion. Also establish the impact on affected communities,
facilities, recreation areas and designated areas using a more realistic ‘quality of life’
criterion of, say, 55dB L Aeq .
❍ Assess the overall requirements for noise reduction measures based on the number of
people affected and the degree to which they are affected.
❍ Do not consider noise in isolation. Assess all noise reducing measures having
consideration for the overall environmental impact (visual, air quality, recyclability and
so on) of the proposed measures.
❍ Depending on the reduction in traffic noise level desired, and the length of road over
which a reduction is required, each of the following noise reducing measures should be
considered, undertaking a financial and an environmental cost–benefit analysis for each
measure in isolation and in combination with the other measures.
❍ Installation of an effective noise barrier as close as possible to the side of the road
(12dB(A) to 15dB(A) reduction local to the road), or
❍ Construction of a flat topped earth bund as close as possible to the side of the road
(8dB(A) to 10dB(A) reduction local to the road, or 12dB(A) to 15dB(A) if combined
with a conventional noise barrier on top).
❍ Resurfacing of the road with a thin surface treatment (3dB(A) to 6dB(A)).
❍ Reducing the volume of traffic on the road (3dB(A) for a halving in the traffic
volume flowrate).
❍ Imposing a lower speed limit on the road, keeping the traffic moving smoothly to
avoid stop/start situations (~1.5dB(A) for a speed reduction from 90km/hr to
70km/hr).
❍ Controlling the number of HGVs on the road (~1.5dB(A) for a reduction from 20%
to ten percent HGVs).

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

171

References
BS5969, 1981

Specification for Sound Level Meters, British Standards
Institution, HMSO, London.

BS5228, 1984

Noise Control on Construction and Open Sites, British
Standards Institution. HMSO, London.

BS 8233,1987

Code of Practice for Sound Insulation and Noise Reduction
for Buildings. British Standards Institution, HMSO, London.

BS4142, 1990

Method of Rating Industrial Noise Affecting Mixed
Residential and Industrial Areas. British Standards Institution,
HMSO, London.

Building Research
Establishment, 1993

The Noise Climate Around our Homes. Building Research
Establishment Information Paper IP21/93.

Commission of the
European Communities, 1975

Environment and Quality of Life (damage and annoyance
caused by noise). CEC Report EUR5398e.

Commission of the
European Communities, 1996

Future Noise Policy. EC Green Paper, COM(96) 540 final.

Department of the Environment, Statutory Instruments, 1975 No. 1763, Building and
1975
Buildings, “The Noise Insulation Regulations”, HMSO,
London.
Department of the Environment, Statutory Instruments, 1988 No. 2000, Building and
1988
Buildings, “The Noise Insulation (Amendment) Regulations”,
HMSO, London.
Department of the Environment, Planning Policy Guidance Note 24 – Planning and Noise .
1994a
HMSO, London.
Department of the Environment, Planning Policy Guidance Note 1 – General Policy and
1994b
Principles . HMSO, London.
Department of the Environment, Planning Policy Guidance Note 13 – Transport . HMSO,
1994c
London.

172

Department of Transport, 1976

Noise Barriers – Standards and Materials. Technical
Memorandum H14/76, Department of Transport, London.

Department of Transport, 1994

Design Manual for Roads and Bridges, Volume 11 –
Environmental Assessment. HMSO, London.

Department of Transport and
Welsh Office, 1988

Calculation of Road Traffic Noise. HMSO, London.

European Commission, 1985

Directive 85/337/EEC. The assessment of the effects of certain
public and private projects on the environment. Council of
the European Communities, 1985.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

European Commission, 1997

Council Directive 97/11/EC of 3 March 1997 amending
Directive 85/337/EEC on the assessment of the effects of
certain public and private projects on the environment.

European Committee for
Standardisation, 1997

EN 1793–1, “Road Traffic reducing Devices – Test Method for
Determining the Acoustic Performance”, CEN, Brussels.

Flindell IH, 1996

Fundamentals of Human Response to Sound. Chapter in Fahy
and Walker (ed): Fundamentals of Noise and Vibration,
Elsevier, London.

Kotzen B and English C, 1999

Environmental Noise Barriers – A Guide to Their Acoustic and
Visual Design. Spon.

Kragh J, 1982

Road Traffic Noise Attenuation by Belts of Trees and Bushes.
Report No. 31, Danish Acoustical Laboratory, Lyngby,
Denmark.

Maekawa Z, 1968

Noise Reduction by Screens. Journal of Applied Acoustics 1,
157–73.

Nelson PM and Phillips SM,
1997

Quieter Road Surfaces, Transport Research Laboratory,
Annual Review 1997.

Organisation for Economic
Fighting Noise in the 1990’s. OECD, Paris.
Co–operation and Development,
1991
Transport and Road Research
Laboratory, 1978

Rural Traffic Noise Prediction – An Approximation. TRRL
Supplementary Report 425

Watts GR, 1995

Acoustical Performance of Parallel Traffic Noise Barriers.
Applied Acoustics, 47, 95–119.

Wilson AH, 1963

Committee on the Problem of Noise – Final Report. Cmnd
2056, HMSO, London.

World Health Organisation,
1980

Environmental Health Criteria 12 – Noise. World Health
Organisation and United Nations Environment Programme,
Geneva.

Wright M, 1999

Thin and Quiet? An Update on New Quiet Road Surface
Products. Institute of Acoustics Bulletin, September/October
1999.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

173

174

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

C HAPTER 7. L ANDSCAPE M ANAGEMENT
7.1 Introduction
What are the most
visible landscapes in
Britain? – the National
Parks, stately homes,
Cornish beaches? No,
the
most
visible
landscapes and indeed
the only ones that many
people see on a day to
day basis, are those
alongside our major
roads. These landscapes
consist of the land
within the highway
boundary and beyond it.
Roads are often the
principal viewpoints for
the wider landscape and
View of Burford from the A40 in Oxfordshire. High quality
are an important means
landscapes can most easily be appreciated from the roads which
for its enjoyment and
appreciation. The A12, pass through them. Source: Jon Etchells.
from Ipswich to the
M25, is 83km long and carries around 35,000 vehicles per day, or something like 11,000,000
viewers every year, assuming only one viewer per vehicle. The extent of these landscapes is
enormous. The Highways Agency estimate that they are responsible for 10,458km of Trunk
Roads in England and around 30,000ha (or 300km 2 , almost the size of the Isle of Wight) of soft
landscape areas on verges, cutting and embankment slopes and around junctions (Highways
Agency, 1997). On non–trunk roads, the area of soft estate per kilometre of road is obviously
less, but the lengths of road involved are vast. Estimates by the Highways Agency indicate that
Trunk Roads are only four percent of all roads in England in terms of length, so non–Trunk Roads
would total around 250,000km – the distance from here to New Zealand and back (six times),
or most of the way to the moon. All of these roads have their own landscapes, even if these are
nothing more than roadside hedgerows.
Much of this highway land is unremarkable and not necessarily attractive and the majority of
the millions of viewers are neither interested in nor impressed by the roadside landscapes past
which they drive. Nonetheless, those who are responsible for the management of these large
chunks of Britain can make a significant contribution to the overall character and quality of the
country’s landscape, by building on and cherishing that which is good and improving that
which can be improved. The aim of this chapter is to provide some basic information as to how
this might be achieved.
Management of our roadside landscapes is important in other ways besides the contribution
they can make to overall landscape quality. Many roads and nearly all of the motorway system,
have been constructed in the last thirty years, with landscapes designed specifically to mitigate
their effects either upon people living within sight of the road or on the landscape in general.
These proposals are carefully worked out and subject to extensive debate and scrutiny at Public
Inquiry, but management is always fundamental to the delivery of planned mitigation – even the
best design will fail without it.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

175

This chapter will therefore provide a brief overview of the principal issues relating to the
management of roadside landscapes, in terms of both management operations such as grass
cutting and thinning of woodland planting, but also in the wider sense of managing and
improving the road network. It will then set out guidelines on current and potential future best
practice, illustrating this with appropriate case studies and give sources for further advice or
information.

7.2 Overview
The concept of extensive, planned landscapes alongside roads (other than the traditional
planting of roadside avenues, usually in urban areas) is a relatively recent one, dating back to
the post war motorway building programme and gathering impetus and sophistication as
opposition to new road building grew in the 1980’s. Early attempts at planting were crude by
today’s standards, with sometimes inappropriate species planted into pulverised fuel ash (PFA)
embankments and left to fend for themselves, with little or no thought given to future
management requirements. Today, a major new road scheme would have been subject to
extensive landscape assessment as part of the statutory approval process and the consequent
landscape mitigation proposals would be implemented as a specialist landscape contract, often
in itself with a value in excess of one million pounds. This initial contract would typically
include a three–year establishment period of relatively intensive maintenance. After which time
there would be a programme of appropriate management so that the eventual aims of each
section of planting were realised, whether the intention was to develop a dense screen, to
provide visual amenity, or to promote nature conservation.
It is in the context of new planting that most people think of landscape management and
maintenance, but of course not all roads are new – many have been on their current alignments
since Roman times or even before. However, even traditional, long–established landscapes still
need appropriate management, if they are not to change and perhaps degenerate.
The organisation and structure of highway management has undergone something of a
revolution in the last few years and is set to change further with the detrunking of many roads.
It is at present divided between motorways and Trunk Roads, which are managed on behalf of
the Highways Agency by a series of Area Maintenance Agents or ‘super agencies’ (24 of them
covering England, with term maintenance contractors in each area. This arrangement will
change in the next few years with the introduction of ‘service contractors’ for each area, formed
by joint ventures of consultants and contractors) and other roads which are the responsibility of
the County or Unitary Councils. These roads, particularly the minor ones, are often managed by
District Councils as agents for the Counties. Some areas have recently set up partnering
arrangements between the two tiers of local government (for example the North Hertfordshire
Highways Partnership, staffed by employees of both the County Council and the District
Council).

7.3 Issues
7.3.1 Improvements
The management of the highway network inevitably involves more than just maintaining the
status quo. There is always the need for review, refinement and improvement to cope with new
standards or increasing levels of traffic. While it is beyond the scope of this publication to
consider proposals for new roads, there are many small–scale improvements that are normally
carried out under the heading of management rather than new construction. These can have
significant implications for the landscape, including the addition or upgrading of lighting, the
provision of hardened strips, new signing, safety fencing, signals and junction improvements.
176

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Some of these improvements now require formal Environmental Assessment (EA) under the
terms of the recent EC Directive (97/11/EC) which amended the former Directive (85/337/EEC)
and increased the number of categories of projects requiring environmental assessment. For an
EA to be required, the criteria now is that the area of the works should exceed one hectare,
including areas for spoil heaps, compounds and storage. However, whether formal EA is
required or not, it is good practice to consider the potential landscape (and wider
environmental) implications of any road improvement project at the earliest possible stage.
Many potential conflicts can be resolved readily at the early stages of planning, but can lead to
difficulty and delay if they are addressed too late.
There is extensive guidance on the assessment of landscape effects and the application of
appropriate design techniques, principally in the Highways Agency Design Manual for Roads
and Bridges (DMRB), Volumes 10 – Environmental Design and 11 – Environmental Assessment,
(Department of Transport, 1993a, 1995). Guidance here will, therefore, be limited to the
suggestion that a landscape architect with experience of highways work should be consulted at
an early stage in the scheme development and be involved in the identification and selection of
options.

7.3.2 Day and night–time landscapes
The equipment available for highway lighting has developed considerably in recent years, with
full cut–off, high–pressure sodium lanterns and more elegant column design. Consequently,
replacement of old lighting by new can often result in significant visual benefits. The
introduction of new lighting into an otherwise unlit landscape can still have dramatic effects
however, particularly if that landscape is sensitive on account of its visual or rural quality, or if
residential properties would be adversely affected. Potential effects to consider are:
❍ views of the columns during the day, particularly views along the road where the columns
will be seen in lines;
❍ views of the bright points of light created by the lanterns;
❍ views of the lit road surface and the moving traffic; and
❍ areas close to the road where light falls onto adjacent properties.
The degree of effects will depend upon the change relative to the existing situation, for example
how well lit the surrounding landscape already is and the degree to which vehicle headlights
are already visible. Some of the greatest effects can be felt where a road is in cutting and vehicle
headlights are therefore hidden from view, but where new lighting columns will extend above
the top of the cutting slopes. Guidance on the assessment of such effects can be found in the
DMRB Volume 11, in Road Lighting and the Environment (Department of Transport, 1993b) and
also in the Countryside Agency publication Lighting in the Countryside: Towards Good Practice
(Department of the Environment and Countryside Commission, 1997). Local Authorities will
also find it helpful to consult the Institution of Lighting Engineers Technical Report No. 24 A
Practical Guide to the Development of a Public Lighting Policy for Local Authorities (Institution
of Lighting Engineers, 1999). A landscape architect with experience of lighting assessment
should be consulted at an early date, as lighting proposals can often be controversial.

7.3.3 Urban landscapes
Roadside landscapes in towns and cities are typically restricted (in terms of plant material) to
rows of trees, though these can make major contributions to the quality of the townscape. Trees
and urban roads are not natural companions and there are inevitable conflicts in terms of
underground services (particularly in recent years with extensive cable TV works), vandalism of
new planting and the requirement to prune the crowns of trees to prevent obstruction or
shading. Useful guidance on the protection of trees is contained in BS 5837 (1991). A simple
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

177

rule of thumb is that any works (including paving, excavation and the alteration of levels)
beneath the canopy of a mature tree must be very carefully considered and professional advice
from a landscape architect, landscape manager or arboriculturist should be sought at the
planning stage. There is a common misconception that trees have a “tap root”, reaching deep
beneath the trunk and that all will be well provided this is not harmed. The truth is that the
majority of the root system is in the top 600mm of the soil and can extend horizontally for a
distance greater than the height of the tree. Reducing levels by 600mm would therefore remove
nearly all of the roots of a tree, leading to inevitable death and probable instability. Many urban
trees will also be protected, either by specific Tree Preservation Orders, or because they are
within a Conservation Area. It is an offence to fell or otherwise harm such protected trees,
without the permission of the Local Authority.
Despite the many pressures, trees must be retained and protected wherever possible. A large
tree can take more than 100 years to grow and only an hour or two to kill outright or condemn
to a lingering death by root severance. Trees provide not only visual benefits, but also in terms
of air quality, temperature regulation and valuable habitats for a wide range of birds and insects.
The hard components of the urban
landscape
should
also
be
remembered – in many older towns
and cities it is the traditional
materials used in roads, footways
and street furniture which help to
determine the character and quality
of the area, tying the townscape
together and producing local
distinctiveness. Any proposals for
highway improvements in such
areas (which will often be
designated as Conservation Areas
by the local authority) must
obviously be carefully considered
and should start with early
consultation with the local
authority planning or conservation
department. The likely requirement
to use traditional materials will also
have an implication for scheme
budgets, though there are many
modern substitute materials on the
market that can be almost as good
in some situations. Repaving of
roads and footways in the historic
core of Bury St Edmunds has
recently taken place using a
sensitive combination of real York
stone footways and traditional style
concrete blocks for the trafficked
areas. Useful guidance is provided
in the series of Historic Core Zone
leaflets, published by English
Heritage, the Historic Towns Forum
and the (former) Department of
Transport. This is not to say that
every scheme should succumb to
178

Recent carriageway and footway resurfacing in the
centre of Bury St Edmunds, Suffolk. A combination of
natural materials (York stone flags, complete with brass
studs to signal crossing points for partially sighted
people), and modern substitutes (tumbled concrete
blocks on the roads). Source: Jon Etchells.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

the craze for Victoriana – traditional materials and street furniture should be used appropriately,
not as a substitute for well–considered design and consideration of modern (or bespoke, where
budgets permit, or in special locations) street furniture. There are many instances where
specially commissioned bollards, railings or other items of street furniture can make a
substantial contribution to the quality of a town centre scheme and can help to create character
and quality where this was previously lacking. The above themes are all addressed in more
detail in Chapter Nine.
Detailed information on urban roads in relation to layout, design, traffic management and street
furniture can be found in the IHT publication Transport in the Urban Environment (The
Institution of Highways & Transportation, 1997).

7.3.4 Suburban landscapes
Suburban landscapes can by definition suffer from the problems and pressures of both urban
and rural areas, but a particular issue is in the definition of the town/country divide and
ensuring that appropriate management is undertaken. Verges in towns will normally be close
mown, while those in the country are cut perhaps twice a year only. The point at which the
transition occurs can be important in signalling the fact that a town or village has been entered
and creating an appropriate sense of place. It can also help to reinforce messages from road
signs and traffic calming measures that the driver has passed into a different environment and
can therefore assist with road safety.

7.3.5 Rural landscapes
Roads
are
extremely
important components of
most rural landscapes,
enabling the landscape to
be seen and appreciated,
but also generating a great
deal of its character, by
means
of
roadside
vegetation,
traditional
fingerpost
signs
and
features such as milestones
and bridges. This character
can often be threatened by
i n a p p r o p r i a t e
improvements
or
management
–
the
Countryside
Agency’s
publication Roads in the
Countryside (Countryside
Commission, 1995) sets
out a range of activities
which
can
have
“cumulative effects in
eroding
countryside
character”:

Pine trees alongside the A11 near Mildenhall, Suffolk. Lines of
trees such as these are an important and distinctive component
of the local landscape. Source: Jon Etchells.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

179

Landscape in miniature – natural vegetation on a Devon bank. Source: Jon Etchells.
❍
❍
❍
❍
❍
❍
❍
❍
❍
❍
❍

widening or easing of bends and removal of boundaries;
white lining and concrete kerbs on remote, rural roads;
inappropriate use of new boundary materials;
over–designed “gateways” to new developments with access off the road;
misguided verge maintenance;
intrusive roadside drains, often replacing open ditches;
heavily signed roundabouts and traffic calming;
excessive and poorly designed lighting;
intrusive safety fencing, noise barriers and mounds;
modifications to, or removal of, traditional bridges, signs and roadside furniture; and
poor treatment of minor roads crossing major new ones.

Any one of these taken singly may have slight effects only and there will undoubtedly be good
reasons for their introduction in most cases, but the overall cumulative effects on the
irreplaceable character of the countryside should always be considered before a final decision
is made. It is important to remember that character is often created by the unusual – by a sharp
bend, or a large tree close to the road or a bank of wild flowers – and that “improvement” in
highway terms usually tends towards uniformity, compliance with standards and conformity
with highways engineers’ expectations, thus homogenising the roadside landscape and diluting
character.
The Countryside Agency concept of “environmental capital” is relevant here. This is an attempt
to assess what matters in the countryside and why it is important. It takes into account factors
such as cultural and ecological characteristics. These may be landmarks relating to local history,
stone bridges, common land and cherished views, or simply the traditional, local means of
enclosure, such as dry stone walling or Devon banks, many of which form roadside boundaries.
The rarity and level of tranquillity of the landscape are also important, as well as the traditional
considerations of the degree of pleasantness of a given view. It is useful to remember that the
importance of a landscape lies not only in its visual appeal or quality. Many landscapes
designated as being of historic interest (for example the Gwent Levels) are not particularly
attractive, but are valued because the landscape contains features and patterns which provide a
valuable link to the past (see Chapter Nine for further information). Viewed in this way, roads
180

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

of all types and scales can be seen as providing a fundamental component of the local
environmental capital, not least because they are so frequently seen and are also the principal
means by which many people actually observe the landscape. Further information can be found
in the Department of Environment, Transport and the Regions (DETR) publication A New Deal
for Trunk Roads in England: Guidance on the New Approach to Appraisal (DETR, 1998).
In terms of ongoing management, many rural roads have reached equilibrium and the
management will tend to maintain the status quo. In such cases careful consideration will be
required before any change in management procedures, even if it appears relatively
inconsequential, such as a variation in the timing of grass cuts. It should also be remembered
that nothing lasts forever and even long–established landscapes are likely to require periodic
management and renewal if they are not to deteriorate. For example, a row of mature trees may
all reach the end of their safe lifespan at around the same time, leading to a radical change in
the landscape if this is not planned for by advance planting of new trees to eventually replace
them.

7.4 Guidance on best practice
7.4.1 Published information
Reference to some useful sources of guidance has already been made above. Other sources are:
❍ The Character of England: Landscape, Wildlife and Natural Features , Countryside Agency
and English Nature, 1997. This is a map, available on paper and on CD–Rom, showing
the natural character areas of England, based on underlying geology, ecology and
landscape character.
❍ Quiet Roads – Taming Country Lanes , Countryside Agency, 1998. This is a leaflet
summarising a new Countryside Agency initiative reflecting the importance of country
lanes for informal recreation and attempting to make them safer and more pleasant to use
for everyone, not just car drivers.
❍ Guidelines for Landscape and Visual Impact Assessment , Institute of Environmental
Assessment and the Landscape Institute, 1995. This publication sets out techniques for
the assessment of potential landscape effects chiefly in terms of new construction
projects, but is also relevant to the assessment of the landscape itself and to the smaller
scale effects which may result from highway improvements.
There is also a wide range of technical information relating to the practice of landscape
management in terms of the preparation of management plans and individual landscape
management techniques and operations. However, this publication does not attempt to provide
such technical guidance, though reference to the overall principles behind it is made below.
Advice to highway managers wishing to find out more about landscape management operations
must therefore be to contact a landscape architect or landscape manager at as early a stage as
possible. Information on contacting local landscape practices can be obtained from the
Landscape Institute and most practices will have some expertise in both landscape design
(which should always take account of future management) and landscape management (which
should always respect the original design intentions).
The remainder of this section will set out in–principle advice on best practice in relevant areas.
This advice will not attempt to provide details of how things should be done, but concentrates
rather on why they need to be done and what they should be trying to achieve.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

181

7.4.2 Landscape design
A landscape design for a highway scheme will, like any design, have a number of objectives –
to create an attractive, appropriate and interesting landscape, to screen given views, to promote
nature conservation or (all too often) to fill left over space. What landscape designs should also
do, but by no means always address satisfactorily, is to provide for future short, medium and
long–term management. Frequently, a designer will have a good idea of the intended effect after
three years, when the plants are established and have begun to grow together, but may not have
thought out what will happen after 10 years, or 25 years. There are understandable reasons for
this – it is inherently difficult to predict the future and clients often are more interested in
immediate effects than more tenuous long term benefits – but for highway landscapes the
medium and long term is often the most important. This can be a particular problem with new
techniques or products. Many motorway–widening schemes used reinforced grass slopes to
create space within the highway boundary and some of these involved geotextiles impregnated
with grass seed. These produced impressive, even growth, in the first year, but much of the grass
was then killed by drought or overheating on south–facing slopes and what is now left is an ugly
combination of rusting steel reinforcement and occasional tufts of grass. In another case, willow
stakes were planted into a reinforced earth embankment, but the design required regular cutting
back of the willows, which otherwise would begin to grow into trees. When it was realised that
future budgets did not allow for this regular maintenance, serious consideration was given to
removing all of the willows, which by then were well established and very vigorous.

Reinforced grass cutting slopes on the M25 in Surrey. The grass has failed due to the hostile
conditions, leaving a maintenance problem for the future. Source: Jon Etchells.
In the DMRB, one of the criteria for landscape assessment is the change in the quality of the
view on a summers day 15 years after the opening year, to allow for development of the
proposed landscape mitigation. Great weight can be put upon this assessment in Environmental
Statements and at Public Inquiries. However, if the design does not provide for future
management and if the commitment to that management in terms of budgets and inspection of
work is not carried through, then the aims of the initial design can be thwarted or diluted and
the level of mitigation provided reduced.

182

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

It is now widely recognised that all new planting requires careful maintenance for an initial
period. At one time this was often for one year only, but is now typically three or five years.
Normal practice is for this initial, or establishment, maintenance to be carried out by the
planting contractor and it is normally combined with a defects liability period, during which the
contractor will be responsible for replacing any dead plants or poorly established areas of grass.
What is not so widely recognised, is that most types of planting, though they may be well
enough established at the end of this time not to need continuous maintenance in the form of
weed control or watering, still need appropriate ongoing management. They cannot be left
alone if they are to grow and mature in the manner envisaged by the design. Trees planted close
together (often as close as one metre centres, to achieve a rapid effect in terms of ground
coverage) cannot be left at those centres, or the result in 15 to 20 years time is a forest of
spindly specimens, none of them capable of survival in the long term and vulnerable to wind
damage. In such an extreme case the only option may be to fell all the trees and start again,
with all the adverse effects in terms of public reaction and expense that would accompany such
drastic action. What is needed to prevent such eventualities is an awareness of future
management on the part of the designer and also the preparation of a management plan.

7.4.3 Management plans
Management plans are the essential tool of communication between those responsible for the
initial design and those who may be undertaking the ongoing management, often 20 or more
years later. A properly thought out management plan will enable the designer to communicate
his ideas (and ensure that he has properly formulated them) and allow the landscape manager
to understand and implement them. It will also enable forward planning of budgets so that funds
are available at the correct time. Such a plan should be set within the context of an overall
environmental management system, preferably based on an ISO 14001 model as outlined in
Chapter Three.
A management plan should set out clearly the aims and objectives which it is trying to fulfil, as
well as the detail of the operations which it is envisaged will need to be undertaken to achieve
those objectives. This is important because after a long period of time there may be many
reasons why the operations themselves are no longer appropriate or possible and the person
attempting to implement and interpret the plan at a later date will need to know what the
intentions were.
Some attempt at this communication was made in the past by means of the Department of
Transport’s Landscape Objectives – these were a shorthand form of a simple management plan,
expressed as LO1, for dense shrub cover, or LO3, for dense tree cover and so on. This system
has now been extended and refined into that of Landscape Functions and Landscape Objectives,
developed by the Highways Agency for use in Design Build Finance and Operate (DBFO)
contracts, where there was a need to set out requirements and benchmarks for standards without
being overly prescriptive. The Landscape Function sets out what the landscape at that point is
intended to do or to achieve, hence LFA is for the provision of screening and LFC is for
conservation of townscape. The Landscape Element, in contrast, is what the landscape consists
of, with LE1 being grass and LE3 being shrubs, each of which can be subdivided. Specific
requirements can also be attached to the Landscape Functions and Elements, in terms of
achieving given stages of growth or coverage by a certain time. They have been used in this way
on DBFO work, but similar standards could also be used as benchmarks against which to judge
the growth and establishment of all highway landscapes. Further development of this system is
under way, as described in section 7.5 below.
In the past the provision of management plans has been on an ad hoc basis, often determined
by the requirements (or otherwise) of individual project managers. Typically there would have
been a handover report produced at the time when a scheme transferred from the Highways
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

183

Agency to their maintenance agent. This would have set out the aims of the planting, the
management envisaged and included as–built planting plans. However, this was not so in every
case and the current Highways Agency super agents have inherited many roads, planted within
the last fifteen years, where they are left to make up their own minds as to what any given area
of planting was intended to achieve and to manage it accordingly.
Management plans must be regularly reviewed for effectiveness and appropriateness to any
changed circumstances and (where relevant) they must also cover considerations such as:
❍ removal of planting which has become over–mature (for example large trees which may
present a safety hazard, or shrubs which have become too large for their position) – not
even trees live forever and planting which may have been appropriate to an area 25 years
ago may no longer be so. In some cases, more appropriate species can be planted, in
others it may be better under current circumstances for there to be no planting;
❍ enrichment of planting, to replace plants which have progressively died over the years, or
to reflect changed circumstances, perhaps in the introduction of some evergreen species
to provide enhanced screening to new housing areas, and
❍ phased replacement, particularly for avenues, such that new, young trees are already in
place and growing when the established trees start to reach the end of their life, avoiding
a situation where there are, temporarily, no trees at all.
While some aspects of the implementation and monitoring of management plans can be
overseen or undertaken by a non–specialist, the formulation and revision of such plans,
including the elements listed above, must always be carried out by a landscape architect or
landscape manager.

7.4.4 Management and maintenance contracts
Once a management plan is in place and there is a budget to pay for the work, a management
contract is normally let. As described above, this will normally follow a period of maintenance
by the planting contractor. At the end of that time the idea is that the planting will be established,
that all (or at least the vast majority) of the plants will be alive and that a longer–term programme
of properly timed management can be developed, as opposed to the intensive initial
maintenance. Management contracts for an individual site can sometimes be let on a one–off
basis, perhaps to carry out some thinning as a standalone operation. For most highway networks,
however, there is a term contract of some kind, whether for the term maintenance contractors to
the super agencies, or for a local authority parks department that may maintain local roads on
behalf of a county council. With Compulsory Competitive Tendering, work for a local authority
may be undertaken by contractors, as opposed to their own staff.
The keys to a successful term landscape management contract are to:
❍ specify it correctly, such that all operations envisaged are properly covered, required
standards are set out clearly and there is little or no room for debate;
❍ select tenderers carefully such that the eventual contractor is committed to the
appropriate level of service provision, not to cutting corners to achieve profit targets; and
❍ to inspect the works, so that payment is geared to performance and standards are delivered.
Current thinking in the Highways Agency is geared towards “partnering” between
specifiers/designers and contractors, to try and apply effort and resources to the achievement of
results, rather than to the all too often adversarial relationship between designer and contractor.
The timing of the management is also critical: many operations, when carried out at the correct
time, require minimum intervention, but will cause more disruption and be more expensive if
delayed.
184

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Thinning of planting on A12 cutting slopes in Suffolk. Source: Jon Etchells.

7.4.5 Management operations
Management Plans are likely to
contain a range of management
operations, according to the nature of
the landscape and the aims and
objectives for it in the future. The
principle operations likely to apply in
most cases include the following:
❍ Mowing of grassed areas at
intervals according to the
standard of finish required. This
will vary between once a year or
less for wildflower or natural
areas (though in these cases the
cuttings may need to be cleared,
which adds significantly to the
cost), to perhaps once a week for
high quality, urban landscapes.
Other considerations to be
borne in mind are delayed
cutting for areas containing
bulbs (no cut until the
above–ground vegetation has
died back, probably in June for
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Considerable visual improvements can be achieved
by simply not cutting the grass. Source: Jon Etchells.
185

daffodils) and also the potential for the presence of protected species of plants, such as
orchids, where it may be an offence to damage them. Many rare species of plants are found
on roadside verges, due to the protection that they have found from outside sources of
interference over the years. In general terms this will only be a concern when past
management practices are changed, as the plants growing on a site will have established
in reaction to the prevailing grass cutting regime. Detailed guidance on appropriate
mowing regimes for areas of nature conservation interest is given in Chapter Eight.
❍ Plant protection will be particularly important in the early years of establishment. Rabbit
fencing or guards will need to be checked for continued effectiveness and stakes will
need to be checked and (importantly) removed once they are no longer required. More
damage is caused to trees by stakes and ties being left on too long and constricting their
growth than by taking them off too soon.
❍ Pruning of shrubs and trees to improve their shape for ornamental species and to produce
a balanced, stable head for individual trees. Pruning is also likely to be required to
prevent obstruction of paths and to maintain visibility requirements, though this is also a
matter where the initial design should have minimised the potential for future pruning to
be necessary.
❍ Thinning of planting plots intended to provide a woodland effect in the longer term.
Where the planting mix contains shrubs only this will be less necessary as the plants can
be allowed to grow into one another. Where the mix contains tree species, they will need
to be thinned so that robust individual specimens are formed (this is important for safety
as well as amenity reasons). The degree and timing of thinning will depend on the initial
mix and density of planting (the greater the initial density, then the more thinning will be
required and the earlier it will be needed). One tree planted in a large space will
obviously never need to be thinned, but 50 trees planted at one metre centres may
ultimately need to be thinned down to only one, if the design intention is to create large
specimen trees. There is an inherent conflict here between short and long term objectives
– one small tree in a large space may look inconsequential initially, but 50 trees in such
a space may lead to greater management requirements (and problems if for some reason
they cannot be applied) in the future. These are the types of consideration that should be
addressed and agreed by all parties at the design stage.
Thinning is an operation that requires a certain amount of knowledge, skill and judgement
on the part of the person carrying it out. It often needs to be selective in terms of species.
For example, taking out half of one species in a planting mix, but only ten percent of the
others and it should always be selective in terms of specimens, retaining the best
individual plants and thinning out the worst, where possible. It must also be carried out in
the light of the design intentions of a given plot. If a dense screen is required, thinning to
produce only a few mature trees may seriously reduce the desired screening effect.
❍ Coppicing of certain species is a useful way of restricting the size of plants while
promoting low level growth for screening. It is a traditional management practice used in
the past for species such as hazel and sweet chestnut and involves cutting the plant back
to a “stool” close to ground level, from which new growth will appear. It is obviously
important to coppice only a percentage of the plants in a given area at any one time,
otherwise all effects of the planting will be lost, albeit temporarily. It is also a technique
which cannot be applied indiscriminately as not all species respond to it and some are
likely to die if cut back close to the ground.
❍ Weed control is a legal requirement in some cases. Landowners, including highway
authorities, have a responsibility, under the Weeds Act 1959, to keep their land free from
infestation by “injurious” weeds, including spear thistle Cirsium vulgare , creeping thistle,
186

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

curled dock Rumex crispus , broad–leaved dock R obtusifolius and common ragwort
Senecio jacobaea .
❍ Replanting is always likely to be necessary in some form, to replace losses, to fill in gaps,
or to cope with changed requirements or perceptions.
❍ Litter Clearance is not strictly a component of landscape management but can be critical
in determining how a given area is viewed and valued. Areas strewn with rubbish will
not be attractive, no matter how successful the planting they contain and the sight of
plastic bags flapping in the breeze from thorn hedges is all too familiar.

7.4.6 Mature trees and safety
The presence of large trees close to
roads, in positions where they could
fall onto the carriageway, is an
obvious source of potential conflict.
Several people are killed each year,
normally during storms, by falling
trees or collision with fallen trees.
However, the only way to be sure of
avoiding this problem would be to
remove all trees that could fall onto a
road, which would cause enormous
damage to the landscape and be
effectively impossible in terms of
logistics or budgets. Instead, a policy
of inspection and appropriate remedial
action is normally followed. The Trunk
Roads Maintenance Manual (TRMM)
requires all such trees to be inspected
annually, whether they are growing
within the highway boundary or
adjacent to it. This inspection should
look for signs of decay or ill health
such as unseasonal loss or thinning of
foliage, dying back of branches, water
staining on the trunk or limbs, growth
of fungi, or looseness around the base
of the trunk. Any tree which shows
such signs, or where other work has
taken place close to it which may have
damaged or severed roots, should be
inspected by an arboriculturalist.
Remedial action may involve lifting or
reduction of the crown of the tree,
securing limbs with wires, lopping or,
as a last resort, felling of the tree. The
highway authority has powers to
require private landowners to
undertake such works where the tree
in question is believed to be
potentially dangerous.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Pine trees alongside the A225 near Sevenoaks,
Kent. The presence of mature trees so close to the
carriageway gives great distinctiveness and
character, but such planting would not be permitted
under current standards. Source: Jon Etchells.
187

TRMM also requires all trees within reach of the road to be inspected at intervals of not more
than five years by an arboriculturalist, who will be able to determine advance signs of many
problems and will be able to make detailed recommendations for ongoing management or
remedial action.
In strictly highway terms, trees close to the road are a potential problem and a drain on
resources but, in overall landscape and environmental terms, they must be regarded as a
precious and finite national asset.

7.4.7 Reinstatement after road works
This is a relatively minor point, but one that can, over a period of years, erode visual quality to
a significant extent. Various bodies will at some time need to excavate within the highway verge
and the quality of their reinstatement can vary between acceptable and non–existent. This can
mean that some areas of grass cannot be mown, as the term landscape contractor will not
normally have the budget to make good such damage. It is therefore important for inspectors to
be vigilant and to require a high standard of reinstatement of all excavations in areas of mown
grass. In many cases this will involve a return to the site to carry out grass seeding in the
appropriate season (April to mid May and September to mid October). Left to themselves, areas
of bare soil will grow rank weeds, not grass.

7.4.8 Hard landscape and street furniture
Areas of hard landscape obviously do not require management in the same way as soft
landscape, but they do require care and attention in the form of regular inspection, properly
timed repair and ultimate replacement. Failure to manage such areas correctly can lead not only
to a decline in visual amenity and the image of any given area, but also to litigation against the
maintaining authority for personal accidents caused by broken or loose paving.
The design of any new or improved areas of hard landscape must also be carefully considered
in terms of layout and materials. In many cases, basic designs and materials can be used with
no adverse effects, but in other areas indiscriminate application of standard solutions and
materials can produce very poor results. This applies to street furniture as well as to paving and
to rural as well as to urban areas. In some villages, the desire to reduce traffic speeds and to
signal the entrances to the village have led to the introduction of visually intrusive signing and
road markings. While the intentions behind such schemes are good, alternative means of
achieving the same ends should perhaps be explored, particularly in visually sensitive areas –
the Countryside Agency publication Roads in the Countryside (Countryside Commission, 1995)
provides advice on good practice.

7.4.9 Serendipity, sensitivity and selectivity
As noted at the start of this chapter, the areas of land involved in the landscape management of
highways are enormous. It will never be possible to sit down and make detailed plans for the
creative management of all of them, neither in most cases is it really necessary nor appropriate.
What is important though, is to make sure that positive planning and management is undertaken
for landscapes which are sensitive by reason of their location, their history, their quality or for
any other reason.
It is also important to recognise that the landscape can develop its own interest with no
deliberate human assistance. Serendipity is defined as “the faculty of making happy and
unexpected discoveries by accident” and many of our most interesting and valuable roadside
landscapes have developed by themselves, over time, as an accidental response to the
prevailing management, or lack of it. There are far more floristically interesting and visually
attractive roadside verges that have developed naturally, in response to the often–poor soils and
188

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Naturally occurring wildflowers on a roadside verge in Hertfordshire. Source: Jon Etchells.
protection from grazing, than have been deliberately sown. Such areas will, being natural, have
the added advantage of being appropriate to their environment and securely established in it.
What is also important is to have the sensitivity to be able to recognise areas of interest, so that
they can then be managed appropriately to protect and enhance the level of interest and to be
able to distinguish between beneficial and adverse change. Such areas are normally known
already, or are brought to the attention of the highway authority by local interest groups, but
there are undoubtedly many others that are not known to the bodies responsible for them. In
this context, the establishment of landscape and ecological inventories (see section 7.5 below)
can be seen as a fundamental step in the more effective management of the soft estate.
Once the knowledge of exactly what level of interest is located where, is obtained and recorded
in an accessible and usable format, then the task of managing with selectivity in order to
promote that interest is made far easier.

7.4.10 Nature conservation
Chapter Eight of this publication deals in detail with the subject of highways management and
nature conservation, but there is an obvious overlap with landscape considerations, if only in
that the two interests will, on the whole, occupy the same areas of land. In most cases, the two
interests will coincide. What is good for nature conservation will be good for the landscape,
particularly if the concept of the landscape as being the sum of the component pasts, including
the underlying geology, ecology and cultural aspects, is used instead of the narrower, more
traditional one of scenic quality and visual amenity. However, in some cases the interests could
diverge, for example when rare plants or animals require a habitat which is not visually
attractive, or where landscape considerations may lead to planting (perhaps for screening) being
suggested, but nature conservation considerations would lead to grassland being preferred. It is
difficult to produce generally applicable rules, but in such cases the level of interest (whether
local, regional or national) would need to be taken into account, together with any potential
effects on local people and any legal responsibilities in terms of species protected by law. Advice
should also be sought from appropriately experienced landscape architects and ecologists.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

189

7.5 Trends and future developments
Extrapolation of recent developments into the future indicates that the environment in general
is likely to be an issue of increasing concern and attention and also that any new roads will
continue to be contentious. This will lead to greater priority being given to the delivery of the
proposed mitigation measures. Cost effective and appropriate management of roadside
landscapes will therefore continue to be important and there seems likely to be continued
pressure for an integrated approach to not only assessment of proposed road schemes, but also
their ongoing management. The DETR guidance in the New Approach To Appraisal (NATA)
(DETR, 1998) is based on the integrated assessment of environmental factors, together with
those relating to economy, accessibility, safety and integration. While NATA is primarily
intended for use in the appraisal of new road schemes, it can be also used in the appraisal of
major maintenance projects as part of the management of the network, where most of the same
principles will apply.
The Highways Agency has recently published its Environmental Strategy (Highways Agency,
1999), which promotes a more proactive approach, seeking opportunities to remedy areas
where the road network is in conflict with the surrounding landscape and townscape, rather
than (as in the past) simply seeking to mitigate the adverse effects of new road proposals.
Another area where the Highways Agency is providing a lead in approaches to appraisal and
management of highways investment is in the creation of Environmental Databases for Trunk
Roads. This work is still in progress, but the intention is to create a comprehensive database,
built around a Geographical Information System (GIS) which will hold the data and be capable
of interrogation. Part of this database will be a Landscape Inventory, in which the whole of the
Trunk Road soft estate will be recorded, divided up into broadly homogenous plots of similar
characteristics. Each one will be given the appropriate Environmental Function (an extension of
the original “Landscape Function” concept, to cover biodiversity, noise attenuation and other
non–landscape functions) and Landscape Element to provide a guide to its present content and
future management requirements. Guidance on this process is due to be issued as an update to
Volume 10 of the DMRB. The overall database will also contain information on nature
conservation and planning and other designations. Many local authorities also have databases
in use or being prepared and this ability to store and extract large amounts of information is
likely to mean that, in future, a lack of information about management intentions and
requirements will be less of a problem. There may also be the opportunity of a link with the
emerging National Land Use Database.
Current Highways Agency policy is to detrunk large parts of the existing Trunk Road network
and pass responsibility for future management over to County Councils or other agent
authorities, leaving the Highways Agency with the motorways and key Trunk Roads only. There
will clearly be issues for debate about the allocation of appropriate funds for ongoing
management of not only the roads themselves, but also the large areas of important landscapes
which will accompany them.

190

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

7.6 Case studies
7.6.1 An urban road – the A316 in West London
The A316 provides an important long distance route to Central London from central southern
and southwest England. It also provides the local connections between the London Boroughs of
Richmond upon Thames and Hounslow, whilst by–passing their principal town centres. The
A316 trunk road links the M3 at Junction 1 (Sunbury Cross) with the A4 at Hogarth Roundabout.
The road passes through outer urban and parkland areas in the west to suburban areas in the
east. It is characterised by relatively wide grass verges, mature street trees and in parts a hedge
in the central reserve of the dual carriageway section. The Highways Agency accepts that
congestion occurs regularly at junctions along the A316 during the morning and evening peak
periods. Major improvements to capacity are discounted. Resources are concentrated on
measures to improve safety, facilities for pedestrians, cyclists and public transport and
environmental enhancement projects including encouraging local sponsor funding for measures
that reinforce highway planting, particularly on roundabouts. The Highways Agency’s
Landscape Strategy for London sets out initiatives to revitalise and upgrade the appearance of
London’s key trunk roads. The Highways Agency recently implemented a major scheme to
replant several hundred street trees in the area, which over the last decade had died or been
removed for safety reasons. Amenity shrub planting and hedges are also being established to
improve the local environment for residents and to strengthen the character and landscape
fabric along the route.
An important element of the Highways Agency’s Strategy is also to upgrade the footways and
highway furniture. This is achieved as an integral part of cyclical and routine highway
maintenance. Thus, whenever a section of road or footway requires repair or renewal, the work
is undertaken using a route–specific “family” of materials, to achieve, over time, an improved
and identifiable character. Standard pedestrian guard–rails are replaced with more ornamental
railings and bollards, painted dark green rather than left with a galvanised finish. Tarmacadam
footways are re–laid using modular slab paviours with coloured block trims and (where space
permits) dedicated cycleways are laid out and marked. Private residential accesses and parking
bays, are better defined to avoid damage to the trees and verges from over–running and car
parking on grass verges. Arboricultural work to mature street trees is undertaken as a rolling
programme to restore vigour, remedy defects and where appropriate control crown spread near
buildings and to maintain height clearances and visibility for road users. The tree surgeons often
work at night, or during roadworks, to avoid the need for extra lane closures or pedestrian
disruption.
This approach enables considerable environmental improvements to be achieved to the urban
landscape over time, without extra traffic disruption and by involving landscape managers and
designers as an integral part of the highway maintenance team.

7.6.2 A rural road – the A30 Okehampton Bypass, Devon
This bypass was opened to traffic in 1989 and was controversial in the planning stages due to
part of its route being within the Dartmoor National Park. It is instructive to use this road as a
case study, because it was the subject of a retrospective assessment in 1997 by the Transport
Research Laboratory – TRL (Transport Research Laboratory, 1997) – of how accurate the
predictions of environmental effects had been and how effective the mitigation measures had
been in addressing them.
Owing to the high quality of the landscape through which it passes, potential visual effects and
the need to address them by careful route selection and appropriate planting were major
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

191

concerns in the planning of the road. The TRL study found that rates of growth of the new
planting were as good or better than those assumed by the Department of Transport at the Public
Inquiry (three to four metres in ten years), illustrating the importance of a good quality planting
specification and appropriate maintenance.
This scheme is also an example of good practice in that a landscape and environmental
management strategy for the bypass was produced by landscape consultants Nicholas Pearson
Associates, on behalf of the managing agents (Forest Enterprise). The results of this review were
fed back into the landscape management in a process of ongoing refinement. The aim of the
strategy was to provide a sound long–term rationale to guide future management, based on a set
of objectives that the planting should be trying to achieve. The methodology consisted of the
division of the planted or grassed areas alongside the new road into plots and each plot was
then allocated a function and a desired content. In areas where the desired content differed from
the actual, additional planting was proposed. The study was undertaken in 1993/94, some five
years after the opening of the road and long–term management was not considered in detail
before this time. While ideally there would have been more consideration of management as
part of the initial design and the communication of this to the managing agent, it is beneficial
in many ways to review the management after the road has been constructed. This is because it
is inherently very difficult to accurately predict all impacts and a retrospective reassessment of
what mitigation may be required and how the planting should be managed, can be very useful
in refining the original proposals.

7.6.3 A suburban road – the A6141 in Letchworth Garden City, Hertfordshire
This is a short section of road around one
kilometre in length, forming the main
entrance to Letchworth Garden City from
Junction 9 of the A1(M). The road has
wide verges (up to 25m on each side)
and a footway on the south side only.
The road is managed by the North Herts
Highways Partnership, with landscape
management undertaken by the contract
services section of North Herts District
Council. While by no means unpleasant,
it was felt that the roadside landscape
could be improved to a standard more
appropriate to the entrance to what is the
world’s first Garden City, founded in
1903 and which still receives visits from
all over the world by students of town
planning.

Wildflowers on the A6141 verge, Letchworth
Garden City. Most of these plants were already
present in the sward and just needed grass
cutting to be delayed in order to grow up and
flower. Source: Jon Etchells.
192

The Letchworth Garden City Heritage
Foundation, which still owns much of the
land in the town, commissioned
landscape
consultants
to
design
improvements to the road as part of an
overall strategy to mark and improve all of
the road entry points into the town. These
proposals were agreed in principle by the
District Council and by the highway
authority and were also put on public
exhibition.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

The final proposals consisted of:
❍ the realignment (to a more natural, flowing line, passing behind trees in places) of the
previously narrow, straight and unattractive footpath;
❍ the creation of low mounds (utilising the spoil from the footpath excavations) to assist in
the separation of pedestrians and traffic;
❍ new tree planting to create variety and interest for road users and pedestrians alike, mass
planting of bulbs (12,000 daffodils and 10,000 bluebells among them), and
❍ the identification of extensive areas where the mowing regime would be reduced to one
cut per year only, in late August, with the intention of promoting wildflowers. The advice
from the District Council was that the additional cost of needing to collect and clear the
cuttings from these areas (when cut only once, the volume of cuttings would be such as
to smother the grass beneath them, if not removed) would be offset by the saving on not
cutting them for the rest of the year.
Work was completed in July of 1998 and the initial three–year maintenance period by the
planting contractor is under way.
While the project has been generally very successful, the following lessons can be learnt from it:
❍ because the project was promoted
by a body other then the highway
authority, it was necessary to enter
into an agreement under Section
278 of the Highways Act and the
general level of bureaucratic
compliance required was very
high. The system (which all parties
were obliged to follow) is designed
to cope with the needs of
developers wishing to create new
accesses onto the highway and
seemed insufficiently flexible to
cope with a body trying to achieve
environmental improvements for
their own sake;
❍ any variation to established and
standard patterns of grass cutting
needs to be very simple and very
clearly set out. In this case,
delineating areas not to be cut, on
drawings and on the ground,
proved to be less of a factor than
the operative being used to cutting
the grass and continuing to do so;
❍ simple changes to roadside
landscapes can be quite effective.
Realigning a path further from the
road and making it into a more
attractive route can increase its use.
Mass planting of bulbs is a cost
effective (12,000 daffodils cost well
under £2,000 to supply and plant),
rapid and dramatic way to create an
improvement, though its duration
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Footway on the A6141 verge, Letchworth Garden
City. The existing footpath was in need of
maintenance and was reconstructed to a sinuous
alignment, further from the carriageway.
Source: Jon Etchells.
193

each year is admittedly short. Also, the simplest change of all can be very effective and
cost nothing – just stopping mowing can create a totally different effect and most swards
already contain some wildflower species just waiting for their chance to grow. This latent
display can be augmented quite cheaply by the planting of wildflowers as individual
small plants or plugs (typically less than 50 pence each). A key consideration here is to
retain some areas as short grass (otherwise people tend to assume that the mowing has
simply been forgotten) and to establish a smooth, flowing line between mown and
unmown areas, as this will form a strong element in most views.

7.6.4 Lighting – A160/A180 Lighting Upgrade
The A160 and A180 trunk roads in North Lincolnshire provide the primary access to the ports
of Immingham and Grimsby, as well as the associated oil refinery and industrial base. This
means they carry significant amounts of HGV traffic throughout the day and night, as well as
serving local residents and commuters.
Apart from the town centres and approaches, these routes were unlit and there was therefore an
increased risk of accidents. The Highways Agency promoted a scheme for extending the
highway lighting, to improve night–time safety and visibility. RPS Consultants undertook an
environmental assessment of the proposals, to ascertain the likely impact, particularly on
surrounding properties. In a flat landscape, road lighting can have a wide visual envelope,
altering the night–time scene for many miles. However, in this case, from many properties the
lighting would be viewed against the background of the brightly–lit oil refinery and other
large–scale buildings. The degree of change in a night–time landscape will depend on the
amount and nature of the lighting being introduced and also the amount of existing light sources
already present.
A number of properties were identified as likely to suffer adverse visual impact and where
practicable mitigation measures, such as screen planting, were proposed to reduce the effects.
In addition, the lighting design utilised full cut–off lanterns, to reduce light spillage and thus
minimise potential effects on adjacent residential properties. This scheme demonstrates the
requirement to consider the balance between highway improvements and potential
environmental impacts and the need to involve environmental consultants at an early stage in
the design process, where relatively minor amendments to the design can help in significantly
reducing the consequential environmental effects.

7.7 Principal recommendations
7.7.1 Preventative measures
The following are the principal measures and attitudes that would be of most value in
preventing adverse effects upon the roadside and wider landscapes as a result of the
management of highways:
❍ There is a large body of relevant published guidance, as referred to above – be aware of
this and refer to it.
❍ Integrate landscape professionals into management teams – this can be in the form of
full–time staff or consultants to be called on when required, but they must be integrated
and aware of the relevant issues and constraints, not just called in when a problem has
arisen.
❍ Develop and review management plans for the soft estate – in many cases these can be
quite simple, but there must be some information on what management is being
undertaken and why.
194

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

❍ Record information on planting and management in a systematic and accessible manner
– in the past there has been too much reliance on personal knowledge.
❍ Think in the long term – will new planting still be appropriate and performing the required
function in 10, 20 or 50 years, or will it have become a problem?
❍ Be sensitive to local environmental character and uniqueness – this needs to be
appreciated, protected and cherished, not homogenised and diluted.
❍ In particular, traditional or historic components of the roadside landscape should be
retained, including traditional boundaries, signposts and hard landscape materials.
❍ Regard mature trees as an irreplaceable (in human timescales) resource, not as obstacles.
❍ The ground beneath the canopy extent of mature trees should not be raised, lowered,
excavated or otherwise disturbed without first seeking specialist advice.
❍ Before commencing any new management operation, or before ceasing or amending an
existing one, be sensitive to the potential environmental effects and seek advice at an
early stage.

7.7.2 Palliative measures
In an ideal world, these would not be required and adoption of the above preventative measures
should go some way towards achieving this objective, but the following are likely to be required
at some time:
❍ Replacement of lost landscape features – these can be either soft in terms of appropriate
planting, or hard in terms of correct use of materials to reflect and enhance local
character.
❍ Reinstatement of the roadside landscape after other works – simple clearance of debris,
levelling and seeding of verges is by no means always carried out.
❍ Consideration in all small scale improvements of the scope for some landscape benefit –
the addition of one tree would not significantly alter most project budgets, but could add
considerably to landscape value over many years.
❍ Remedial management where correctly timed management has not been undertaken in
the past – this can be more time consuming and expensive, but is often required.

References
BS 5837, 1991

Guide for trees in relation to construction.

Countryside Commission, 1995

Roads in the Countryside.

Department of the Environment
and Countryside Commission,
1997

Lighting in the Countryside : Towards Good Practice. HMSO,
London.

Department of Transport, 1993a Design Manual for Roads and Bridges , Volume 11
(Environmental Assessment). HMSO, London.
Department of Transport, 1993b Road Lighting and the Environment . HMSO, London.
Department of Transport, 1995

Design Manual for Roads and Bridges , Volume 10
(Environmental Design). HMSO, London.

DETR, 1998

A New Deal for Trunk Roads in England. Guidance on the
New Approach to Appraisal. DETR, London.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

195

Highways Agency, 1997

Annual Report, 1997–98. Highways Agency, London.

Highways Agency, 1999

Environmental Strategy. Highways Agency, London.

The Institution of Highways
& Transportation, 1997

Transport in the Urban Environment. IHT, London.

Institution of Lighting Engineers, A Practical Guide to the Development of a Public Lighting
1999
Policy for Local Authorities, Technical Report No 24. ILE,
Rugby.
Transport Research Laboratory,
1997

196

The Impact of the Okehampton Bypass,
Gordon Mudge and Linda Chinn, Transport Research
Laboratory Report 268. TRL, Crowthorne.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

C HAPTER 8. T HE M ANAGEMENT OF E COLOGY AND
B IODIVERSITY
8.1 Introduction
The importance of roadside areas for nature conservation has been recognised for many years
(for example, Tansley, 1949; Elton, 1966; Way, 1973). Like all semi–natural habitats, their
potential and actual value for wildlife is primarily dependent upon the way in which they are
managed. Local authorities manage most highway verges, with traffic safety and perhaps
aesthetic considerations as the main defining factors. During the last fifty years, attention has
been given to the environmental implications of management regimes adopted by highway
authorities and some notable attempts have been made to develop management principles that
encourage wildlife and satisfy highway engineers. In this chapter, the history of highway
management and nature conservation is briefly reviewed and some recent and current initiatives
are described.

8.2 The importance of roadside areas for nature
conservation
The total area of roadside verges in the UK has been estimated as 212,200 hectares (Crofts and
Jefferson, 1994). As a comparison, semi–natural grasslands in the United Kingdom are thought
to cover some 85,000 hectares (Crofts and Jefferson, 1994). Not only the total area of roadside
verges but also their continuity confers considerable potential for botanical and zoological
interest. In the post–war period, there have been overwhelming moves from the long–practiced
traditional methods of farming to intensive agriculture, coupled with the development of land
for housing, industry and roads. These have resulted in an ever–declining area of semi–natural
habitats within the UK. In addition, those areas that have been retained are often isolated from
other similar areas, further reducing their value. Old, undisturbed verges are frequently the only
unimproved grasslands found in the counties of lowland Britain. Verges along modern roads do
not have an historic link with semi–natural vegetation and its associated animals and thus do
not have the innate value of old verges. Nonetheless, they do provide a large area of potential
wildlife habitat. Modern roads, especially motorways, are designed with gentle curves and
gradients, these being achieved by means of frequent cuttings and embankments, often of
considerable size. Consequently, verges of such new roads are sometimes more than 50m wide.
Whilst their value as a repository of unimproved grassland is perhaps paramount, roadside areas
also include ditches, hedges, trees and areas of scrub. These not only have intrinsic importance
but also contribute to the overall value of the roadside to wildlife by providing a mosaic of
vegetation structure and habitat types. An idealised verge is shown in Figure 8.1.

8.3 History of highway management and implications for
wildlife value
Until roads were surfaced, people, animals, carts and coaches used the whole width of the
“highway”. The highway was often deliberately quite wide in order to allow people to avoid
holes, puddles, muddy areas, fallen trees and so on and to allow animals to be herded between
fields or to market. Carts, coaches, horses and other animals caused erosion and poaching. In
winter, highways often became impassable. Jane Austen, amongst other contemporary
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

197

Figure 8.1: The “ideal” road verge (from Pound and Waite, 1994).
Courtesy: Kent Wildlife Trust.
commentators, complained of the condition of highways. As the Industrial Revolution gained
momentum, the pressure to improve the quality of roads increased. In the early nineteenth
century, new methods of road surfacing were developed and those of John McAdam proved
sufficiently cheap to be widely used (Pound and Waite, 1994). The construction of good
surfaces meant that people and vehicles no longer needed to use the entire width of the
highway. Consequently, grass verges were left either side of the surfaced road, between its edge
and the boundary feature (usually ditches and/or hedges). By 1900, many major routes were
surfaced. The arrival of the motor car increased the demand for surfaced roads and in the 1930s
and 1940s, important minor roads were surfaced (Pound and Waite, 1994). The Milk Marketing
Board was responsible for many improvements to minor country roads in the 1930s in order to
allow milk tankers to reach collection points (Way, 1973).
Although the verges were no longer used as a highway, they retained their secondary function.
Under the traditional, frugal farming practices of the past, roadside areas had always played a
small but not insignificant role. Hay crops were usually taken, sometimes supplemented or
replaced by grazing. Such established methods of management prevented the development of
coarse grasses and scrub and maintained a species–rich meadow flora.
In the post–war period, agricultural practices changed and the management of roadside areas
passed from farmers to highway authorities. Hand–cutting by scythes and/or grazing was
inevitably replaced by the use of machines and herbicides. By the 1950s, there was concern
about the widespread use of herbicides. Following representations by the former Nature
198

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Conservancy, the then Ministry of Transport issued a circular to local authorities advising them
on more appropriate and responsible use of herbicides (Ministry of Transport and Civil Aviation,
1955). In the early 1960s, the use of growth retardants in combination with herbicides was
suggested as a routine maintenance method that would in some cases eliminate the need for
roadside mowing. However, by the mid–1970s, the routine use of chemical sprays had more or
less ceased, due to questions about their effectiveness, their cost and opposition by nature
conservation bodies and the public. Today, their use is mainly restricted to situations such as
the central reservations of motorways and dual carriageways where cutting is inappropriate.
In addition, in the 1970s, mowing became less frequent. In July 1975, the Department of the
Environment instructed that grass–cutting on land forming part of trunk roads and motorways was to
cease as a regular practice in order to reduce highway maintenance costs. Since then, the majority
of verges have not been cut other than a narrow band close to the carriageways. Consequently,
coarse grasses and tall herbs are dominating many verges and bramble and scrub are invading.
The results of a telephone questionnaire to all highway authorities in the early 1990s suggested
that whilst 67% of the 64 highway authorities questioned, considered that they had a roadside
verge wildlife conservation policy, the lengths of verge managed specifically for nature
conservation were very limited (Alexander, 1995). An average of just over two percent of the
total verge length was managed for nature conservation.

8.4 Highway management and nature conservation
8.4.1 Conflict between highway safety and nature conservation
Where there is a conflict between the management that will maximise the wildlife value of the
roadside area and the safety of traffic and pedestrians, then clearly road safety must almost
inevitably take priority. The key to developing responsible management for nature conservation
is to ensure that wherever possible any general prescriptions are both practical and in tune with
those required for safety. As with all semi–natural habitats where the primary land use is not
nature conservation per se, appropriate management is most likely to be consistently applied
where it does not conflict with the “normal” land use, be it agriculture, recreation or whatever.
Nonetheless, the conflict between highway safety and nature conservation should not be
overemphasised. In at least one crucial factor, the aims are the same: neglect results in verges
becoming dominated by tall herbs and then scrub. Such verges lose their nature conservation
value and reduce visibility. Furthermore, it is difficult and costly to keep such vegetation low if
infrequent management is introduced.

8.4.2 Conflict between nature conservation and other uses of the verge
Over the last 100 years or so, verges have developed a new role: that of harbouring the utilities:
drains, electricity cables, telephone and other cables, gas mains and so on. The introduction
and maintenance of such utilities cause considerable disturbance to roadside communities.

8.4.3 Responsibility for environmentally led highway management
Whilst the responsibility for roadside maintenance is clearly defined, the number of different
players involved, particularly once nature conservation or other environmental issues are
introduced, makes it difficult for control to be applied. Thus, the highway authority’s prime
responsibility is to road safety. English Nature, the county wildlife trust, the county council’s
ecologist and others may wish to introduce management appropriate for wildlife. The utilities
and the local planning authority need to be kept informed of any “special” verges, as do
adjacent landowners (who will own the subsoil of the verge in most cases) and local residents.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

199

The actual management itself may be carried out by the highway authority’s contractors, by
other council groups (for example, countryside project staff), by landowners, by volunteers or
by a combination of these. It is no wonder that the management that is so carefully devised and
considered is sometimes not implemented on the ground.

8.4.4 Costs of highway maintenance
Even more influential than the needs of highway safety in defining the management that is
implemented on roadside areas is perhaps its cost. Highway authorities inevitably have limited
budgets and the management of verges for wildlife may be an aspiration that does not match the
priority of other budget headings.

8.4.5 Conflicting needs of different species
One of the major problems in identifying appropriate management techniques for roadside areas
lies in the conflicting needs of different species. Roadside verges have been recorded as
supporting breeding populations of:
❍
❍
❍
❍
❍
❍

40 of the 200 species of birds found in the UK;
20 of the 50 species of mammal;
all six reptiles;
five of the six species of amphibian;
25 of the 60 species of butterfly, and
eight of the 17 species of bumble bee.

Around 900 of the 2000 species of plants are associated with roadside areas (Way, 1977). It is
inevitable that general management prescriptions could never encompass the needs of such a
varied array of plant and animal species.
Clearly, the problem is exacerbated where the existing (and potential) ecological status of an
individual roadside area is not known. The importance of field survey information about
highway verges, identifying communities, populations and features of particular significance for
nature conservation cannot be over–emphasised. Only through an adequate understanding of
the biological character of verges can effective management be defined.

8.4.6. Lack of research
Even where the nature conservation value of a verge is well understood, the implications of
various management techniques are rarely appreciated. There is a clear need for monitoring the
effects of management upon the quality of verges, at all levels. Monitoring the effects of
management is not straightforward. Changes are often almost imperceptibly slow and other
factors, such as the weather or natural population cycles, may complicate the direct effects of
management. Some changes are so imperceptible on a year–to–year basis that they are revealed
only by looking at the cover or abundance of individual species. Such research requires skill,
experience and time.

8.4.7 Possible conflict with visual and landscape aspirations
The creation of new verges, particularly in urban areas, offers the landscape architect an
opportunity to create attractive, low–maintenance vegetation. Particularly where such
vegetation is composed mainly of species of tree, shrub and grass that do not naturally grow in
the United Kingdom (so–called non–native species), the wildlife value of such areas can be
minimal. In recent years and particularly in rural and semi–rural areas, there has been
increasing emphasis on the use of native species of local provenance, with concomitant cost
200

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

implications. Along urban roads (notably dual carriageways), the narrow and often shaded
ribbons of roadside habitat have little wildlife potential and the use of native species might be
regarded as less important. However, where larger verges are present, their value for wildlife
can be relatively high within an urban environment with little potential habitat.
As with the issue of potential conflict with safety demands, the issue of conflict with visual and
landscape aspirations should not be over–emphasised. Areas of native vegetation can have
considerable aesthetic appeal. Ecologists and landscape architects often have similar aims, in
that in order to create a low maintenance area, low nutrient substrates are used, encouraging
the development of habitat with a higher species diversity and a greater number of species of
note.
Landscape issues are discussed further in Chapter Seven.

8.5 Issues
8.5.1 Frequency and timing of cutting
The frequency and timing of cutting are key elements from the point of view both of
conservation and of highways maintenance. The highway authority cuts verges to ensure that
people can use roads and pavements safely. In urban areas, verges are usually cut around six
times a year between March and November in order to keep grass shorter than 15cm. County
Councils usually fund around six cuts. Borough, district or parish councils may make additional
cuts at their own expense, for example verges within Harrogate Borough are cut 12 times per
annum. The short grass is tidy and allows potentially hazardous debris to be exposed (and
removed). The frequency of cutting is often increased where complaints are received from the
public, who push for more manicured grass. People who have moved from urban and suburban
areas into the countryside often carry their expectations of “lawn–like” verges to their new
village locations. Best Kept Village competitions also encourage aspirations of frequent mowing.
In rural areas, the outer one metre of major road verges is usually cut twice or three times a
year; sightlines are cut more frequently in order to maintain visibility. On minor roads, the outer
one metre of verge may be cut only once (usually in the autumn). The entire verge may be cut
once a year (for example, Buckinghamshire), every three years (for example, Derbyshire, Devon
and Hampshire), every five years (for example, County Durham) or not at all (for example,
Bedfordshire and North Yorkshire). In both nature conservation and aesthetic terms, it is
appropriate to time any cuts to allow at least key flowering plants to bloom and set seed.
As mentioned above, the problem today, at least in rural areas where most of the verges of
nature conservation significance are located, tends to be not so much one of over–cutting but
rather one of no cutting. The outer one metre of verges is usually of lesser interest than the
vegetation further from the road edge; it is frequently subject to salt damage, smothering with
dirty spray and erosion from pedestrian traffic and tyre damage. The cutting regime imposed on
the outer one metre strip is thus of comparatively little significance in determining the wildlife
value of the overall verge. Rather, if the main verge area remains uncut from year to year, coarse
grasses and tall herbs such as hogweed Heracleum sphondylium , cow parsley Anthriscus
sylvestris and creeping thistle Cirsium arvense will be able to spread unchecked and the
shade–intolerant flowers which are characteristic of old meadow swards will gradually be lost.
In addition, woody species like elder Sambucus nigra , hawthorn Crataegus monogyna and
bramble Rubus fruticosus agg. begin to colonise the verge. Eventually, the grassland will turn to
scrub. Whilst scrub does provide a habitat for many animals, it is a much more common and
easily re–created habitat than semi–natural grassland. In management terms, scrub is difficult
and costly to eradicate once it has established on a verge, and even if the scrub is controlled,
the grassland beneath may have permanently lost its interest.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

201

Where verges are cut, cuttings are not collected and removed by highway authorities, primarily
for economic reasons. In this important sense, mowing verges does not mimic a hay cut, where
the removal of the forage helps to maintain a relatively low–nutrient soil that is essential for
species–rich grasslands to flourish.

8.5.2 Use of chemicals
As discussed above, chemicals such as herbicides, other pesticides and growth retardants are
rarely used today in routine roadside maintenance. Clearly, their indiscriminate use would have
considerable implications for wildlife found in the verges.

8.5.3 De–icing compounds and other pollutants
As with herbicides, de–icing salts are used less extensively today than in the past. In this
country, the de–icing agent applied is common salt (sodium chloride) in an almost pure form.
Storage of salt on verges causes direct effects and can prevent mowing. Few traditional
grassland species of plant or animal are able to tolerate salt. On the main roads where salting
is common during icy periods, the development of salt–tolerant species along the edges of
verges has been noticeable.
At least on roads where traffic speeds are low, the depth of verge directly affected by pollutants
is small. Where speeds are higher, there is frequently a hard shoulder, which protects the verge
from high levels of pollutant–laden spray. Analysis of the soils and vegetation from transects
taken across motorways has shown that central reservations experience the highest
concentrations of various pollutants. Concentrations decrease rapidly on the outside verges; at
a distance of five metres from the hard shoulder the concentration of salt in the soil is negligible
(Colwill, Thompson and Ridout, 1976; Thompson, Rutter and Ridout, 1986), although spray
damage to sensitive vegetation (notably conifers) has been detected up to 40 metres from the
highway in other countries (Colwill, Thompson and Rutter, 1982). A typical distribution pattern
is shown in Figure 8.2. There may, however, be more significant effects where ditches are found
close to the road or where drains carry runoff to ditches deeper into verges. Salt applications
later in the season in response to late frosts are likely to be particularly harmful by causing high
concentrations of salt to persist into the growing season. A dry spring will further increase the
concentration of salt remaining in the soil by reducing leaching. A full discussion of the effect
of seasonal maintenance practices can be found in Chapter Four, section 4.4.5.
Of other pollutants, the contamination of roadside soils by lead was widely reported in the
1970s but there was little evidence to suggest that the vegetation on the verges was adversely
affected (Thompson, 1986). In a soluble form, lead is a plant toxin but it is rapidly immobilised
by adsorption and precipitation in the surface layers of the soil, becoming largely unavailable
for uptake by plant roots. Furthermore, lead as a factor affecting roadside habitats has decreased
in significance as lead concentrations in petrol have been progressively reduced since 1973
(Hickman, 1989: see also Chapter Five, Box 5.3) and completely eliminated from 1 January
2000, except in a very limited number of cases. However, this has caused increasing concern
about the influence of additives such as MTBE in lead replacement petrol particularly with
regard to air quality effects (see also Chapter Four, section 4.4.1).
Concentrations of oxides of nitrogen may reach 0.8ppm beside busy roads, compared with a mean
maximum concentration of 0.05ppm in clean air (Mansfield, 1979). Plants take up both NO and
NO2 through the leaves, suggesting that near roads the nitrogen content of plants may be
increased, stimulating the growth of insect populations (for example, Port and Thompson, 1980).
Carbon monoxide has an effect only at concentrations above 100ppm, which are rare, at least
on motorways (Colwill, Thompson and Rutter, 1982). Ethylene is the most harmful of the
202

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

5

●
●

2

1

●

Verge

5
10m

0

250

500

750

1000

1250

●

●

●

2

1

●

●

0.5

Road
Surface

●

0.5

1

●

Central
Reservation

0.5

Road
Surface

●

0.5

1

●

2

●

Verge

10m

●

95% Confidence limits
●

1500

1750

Exchangeable sodium (ppm)

Figure 8.2: Distribution of sodium in soils on a typical transect across the M62 motorway,
sampled in April 1974 (from Colwill, Thompson and Ridout, 1976).
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

203

hydrocarbons associated with vehicle exhaust emissions. However, the characteristic effects of
the gas have not been seen on verges, perhaps because ethylene–induced damage is associated
with temperatures higher than those found in the United Kingdom (Davison and Wharmby,
1979). Other pollutants result from photochemical reactions in exhaust emissions. Some, such
as ozone and peroxyacetyl nitrate, are known to be phytotoxic under some conditions (Colwill,
Thompson and Rutter, 1982). However, as the photochemical reactions are not immediate, it is
likely that the phytotoxic chemicals are not found in high enough concentrations on verges to
have a significant effect on roadside species.
Other pollutants are also associated with roadspray and runoff, including oils and residues from
brakes, tyres, clutch plates and the road surface. The precise nature of the pollutants carried in
the spray is usually secondary to its general smothering effects, caused by particulate
deposition. Colwill, Thompson and Rutter (1982) reported that exhaust dust applied to leaves at
a density comparable to that observed by busy motorways reduced photosynthesis by about
20%. This level is likely to contribute to reduced growth. The effects of dust on plants are
complex, ranging from increased absorption of solar radiation to decreased gaseous exchange
between leaves and the atmosphere.
These issues are discussed further in Chapters Four and Five.

8.5.4 Erosion and disturbance
Tyres can damage roadside areas where vehicles drive over or park on verges. Installation of
kerbing designed to prevent such erosion causes disturbance, which is also associated with the
introduction and maintenance of services, such as sewers, electricity and telephone lines, and
gas mains. Occasional erosion or disturbance is usually “repaired” by the introduction of topsoil
and grass seed. In general, the latter fulfils an aesthetic rather than a nature conservation
function, as seed mixes are usually standard commercial amenity mixes and the use of topsoil
introduces nutrients and weed seeds to roadside areas. There is also the risk of the introduction
of Japanese knotweed Fallopia japonica , a pernicious weed that spreads rapidly and is difficult
to control.

8.5.5 Economic and practical considerations
Ultimately, the main issue affecting roadside management is cost. Highway authorities have
limited funds that must be directed towards ensuring highway safety, rather than environmental
protection. Clearly the threat to the wildlife value of verges today lies not in the over–frequent
cutting and herbicide use common in the past, but rather in neglect.
Even where nature conservation issues are clearly identified and the general maintenance
regime amended to accommodate features of particular interest, problems occur. These have
become more acute in recent years as private contractors and sub–contractors, many of whom
are employed on annual contracts, now carry out most roadside maintenance. Consequently, all
deviations from the general regime have to be laboriously spelled out in contractual details and
their implementation relies upon effective communication between the various parties involved.
Some highway authorities have developed special incentives to encourage contractors to ensure
that their staff implement special management carefully. In Devon, contractors are paid by the
lengths of verge included in their contracts, with areas of fine flowering stems which are to be
avoided, not deducted from their total length (and thus payment). In Cornwall, contractors are
fined where they erroneously cut areas that are to be avoided.
Another consequence of using contractors is that cutting regimes now tend to be defined by
programme (for example, requiring three cuts between March and July), rather than need (for
204

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

example, requiring the vegetation to be kept below a specified height). In this way, unnecessary
cuts may be made or mowing carried out at a time convenient to the contractor, rather than
when the weather conditions have resulted in a surge of plant growth.
Many of the ecologists interviewed in the preparation of this chapter lamented the passing (in
the 1960s) of the old “lengthman” system of roadside maintenance. Under this system,
individuals worked their own lengths of verge, year after year, and thus became truly familiar
with any special features of interest.

8.5.6 Communication
As mentioned in Chapter Seven, the organisation and structure of highway management has
undergone something of a revolution in the last few years and is set to change further with the
detrunking of many roads. It is at present divided between motorways and Trunk Roads, which
are managed on behalf of the Highways Agency by a series of Area Maintenance Agents or
“super agencies” (24 of them covering England, with term maintenance contractors in each
area. This arrangement will change in the next few years with the introduction of “service
contractors” for each area, formed by joint ventures of consultants and contractors) and other
roads which are the responsibility of the County or Unitary Councils. These roads, particularly
the minor ones, are often managed by District Councils as agents for the Counties. Some areas
have recently set up partnering arrangements between the two tiers of local government – the
example was given in Chapter Seven of the North Hertfordshire Highways Partnership, staffed
by employees of both the County Council and the District Council (see also section 8.6.5).
The key issue of communication between ecologists, highway engineers and contractors is
mentioned above in section 8.4. Communication between ecologists, highway engineers and
the public is also essential. The public needs to be helped to understand that management for
wildlife frequently does not result in the type of tidy verge that they may expect or prefer. Many
authorities have prepared information sheets, such as Surrey County Council’s Your guide to
grass cutting on highway verges.
Effective communication requires that there is a commitment to the objectives of the
management and that the appropriate systems are put in place (for example, within the
framework of an overall ISO 14001 EMS as mentioned in Chapter Three). As information
technology becomes more predominant, the role of Geographical Information Systems (GIS) can
be useful in ensuring that the boundaries of special verges and their important features are
easily (and thus frequently) accessed. East Sussex County Council has kept a schedule of
protected verges for over 20 years. Protected verges have specific management plans that are
kept on a Geographical Information System and are issued to service providers such as British
Telecom and others who might carry out work on protected verges.

8.5.7 Other, non–highway factors
The wildlife value of roadside areas is influenced not only by highway maintenance but also by
the adjoining landuse. Thus, for example, many verges are still subject to herbicide application
not for verge management purposes but because of herbicide drift from agricultural production
in adjacent fields. Similarly, there may be leaching or inadvertent spreading of fertiliser from
adjacent farmland. Hedges and ditches, which are often important components of roadside
areas, are usually managed by landowners rather than the highway authority.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

205

8.6 Legislation and responsibilities
Some roadside areas have recognised nature conservation significance of such value that
environmental issues become of paramount concern and consequently have a direct influence
on highway maintenance. In some cases, areas may have statutory protection or may contain
species that are afforded special protection under law. Elsewhere, local bodies such as county
wildlife trusts may have identified verges of local significance where routine cutting regimes
may not be appropriate. Again, the implementation of good management is dependent on
effective communication between ecologists, the highway authority and its contractors.

8.6.1 Statutory designations
Two types of statutory designation may encompass roadside areas: Sites of Special Scientific
Interest and Local Nature Reserves. Sites of Special Scientific Interest are notified under the
Wildlife and Countryside Act 1981 and were afforded additional protection under the
Environmental Protection Act 1990. Local Nature Reserves are established under Section 21 of
the National Parks and Access to the Countryside Act 1949. In addition, the government has
responsibilities under international agreements and European Union directives. Any sites
identified as being of European or international importance are protected as Sites of Special
Scientific Interest in the UK.
There may be ambiguity about the boundaries of Sites of Special Scientific Interest (SSSI) in
relation to verges, as it may not be clear whether the boundary of the site lies at the back of the
roadside area or along the edge of the highway itself. To–date, no verges on their own have been
designated as SSSIs, although some of the Breckland heath SSSIs are mainly verges, for example,
Cherry Hill and the Gallops SSSI.
Under the Hedgerow Regulations 1997, permission to remove a hedge must be obtained from
the local planning authority. This will be refused if the hedge is “important”, as defined by the
Regulations. “Important” hedges may be of historic or biological significance.
Some hedgerow or roadside trees, particularly in urban or suburban areas, may be protected by
Tree Preservation Orders. These prohibit any significant works to trees without the written
consent of the local planning authority and, in some cases, of the Forestry Authority.

8.6.2 Non–statutory designations
Where biological field surveys have identified species or communities of interest, relevant
verges may be designated as Sites of Importance for Nature Conservation or equivalent. Such
sites are defined by county wildlife trusts and most local authorities use schedules of these
so–called second tier sites to inform their decision–making on development. However, most
counties have a specific designation for verges of value, such as Heritage Verges in
Hertfordshire, Rural Verges of Ecological Interest in Hampshire and Verges of Special Interest in
Lancashire.

8.6.3 Protected species
The Wildlife and Countryside Act 1981 and subsequent legislation, lists those species of plants
and animals that are afforded statutory protection. Under the Act, all wild birds, their nests and
eggs are protected. Schedule 1 of the Act lists those birds that are protected by special penalties.
Certain other wild animals are protected under Schedule 5. It is an offence to kill, injure or take
animals listed in Schedule 5, to intentionally obstruct, damage or destroy a “shelter” used by
them or to disturb the animal whilst in such a shelter. Schedule 5 species include bats, hazel
206

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

dormice and great crested newts. Under the Act it is an offence to pick or intentionally uproot
or destroy any wild plant included in Schedule 8. The Wildlife and Countryside Act 1981 is also
the local instrument by which species for which the United Kingdom has special responsibilities
under international agreements and legislation are protected. Badgers are singled out for
specific legal protection in Britain, under the Protection of Badgers Act 1992.
The occupier of land is required by the Weeds Act of 1959 to control “injurious” weeds,
including spear thistle Cirsium vulgare , creeping thistle, curled dock Rumex crispus ,
broad–leaved dock R. obtusifolius and common ragwort Senecio jacobaea . In practice, the
Ministry of Agriculture, Fisheries and Food is only likely to exercise its right to demand the
control of such species where there is a real threat to agricultural production. Some Local
Authorities, such as Cornwall County Council, actively encourage landowners to control such
weeds, including Japanese knotweed.

8.6.4 Role of English Nature
English Nature is the body responsible for advising government on nature conservation in
England. Its work includes the identification and notification of Sites of Special Scientific
Interest and the provision of advice on nature conservation to all.

8.6.5 Role of local authorities
Local authorities have a multiple function in the management of roadside areas. Firstly, the
highway authority for most roads is the local authority (with the highway authority and its
agents taking responsibility for motorways and trunk roads). Highway engineers are responsible
for road improvements and other capital works, with other highways staff responsible for
maintenance. The maintenance itself is usually carried out by the council’s contractors. In
Hertfordshire, the management of the seven Heritage Verges is carried out by the Countryside
Management Services, which is jointly funded by Hertfordshire County Council and the district
councils. Secondly, some county councils employ ecologists who will advise on the appropriate
management of verges of recognised nature conservation value and may be involved in the
identification of such verges. The local planning authority is responsible for some highways
matters, such as liaison with utilities and with the administration of Tree Preservation Orders.

8.6.6 Role of county wildlife trusts and other naturalists
As mentioned above, county wildlife trusts are usually responsible for the definition of Sites of
Importance for Nature Conservation. Some trusts have organised district/borough–wide or
countywide surveys of roadside verges. It is often local naturalists, who are experts in particular
species groups and may be members of county wildlife trusts or other local natural history
societies, who first locate species of interest in verges. Such information is usually held by
county wildlife trusts and/or county biological databases. In a few counties, such as Kent (see
8.8.2), Essex, Lincolnshire and Cumbria, county wildlife trust members act as volunteer wardens
for roadside nature reserves. The role and responsibilities of volunteer wardens are well
presented in Pound and Waite, 1994.

8.6.7 Role of landowners
The management of hedges and/or ditches found along verges (usually at the back of verges) is
generally the responsibility of landowners. In some areas, such as Lincolnshire, the management
of verges is also undertaken by (adjoining) landowners, sometimes with the advice of local
authorities and/or others (such as Farming and Wildlife Advisory Group advisers).
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

207

8.7 Guidance on best practice
When looking at best practice for the management of roadside areas, the distinction should be
made between “ordinary” verges and verges of note for nature conservation. It would be
disingenuous and indeed inappropriate to suggest that money and effort be directed towards the
wholescale enhancement of “ordinary” verges, in a climate when verges of note are currently
receiving little or no special attention on a nationwide level. In contrast, Hertfordshire County
Council is currently redefining roadside maintenance contracts so that different areas of the
county are cut at different times, defined by the vegetation type. Thus, for example, chalk
grassland would have a full cut specified every three years. The aim is to incorporate Heritage
Verges (which have their own specific management regimes at present) into the new scheme,
with appropriate monitoring to ensure that their special interest is not lost under a more general
maintenance prescription.

8.7.1 Assessment of roadside areas
Few counties have undertaken a systematic survey of roadside areas. It is more commonly the
case that verges of interest have been identified in an ad hoc fashion as a consequence of the
interest of local naturalists. Initially, the fact that only a few verges of interest are recognised
and designated allows appropriate management for them to be devised and tested. Ultimately,
the proper preservation of a county’s roadside resource requires a more methodical approach.
Several counties have targeted roadside areas as a priority habitat for action plans. Thus,
Cambridgeshire, for example, has a Habitat Action Plan recommending a different cutting
regime for verges of interest, with cuttings to be removed. The Plan includes short and
long–term management objectives, with targets for the next three years and is reviewed
annually. East Sussex aims to have completed its Biodiversity Action Plan for verges by the end
of 2000 and Cheshire is currently preparing its Biodiversity Action Plan.

8.7.2 Cutting regimes
Way (1969 and 1977) showed that it was possible with a single cut during the period of
maximum growth (late May), or at the most a second in June, to maintain the height of a sward
at 30cm. This is because the flowering stems of most taller species do not regrow once they
have been cut, leaving the height of the vegetation restricted to the height of the basal leaves.
However, whilst cutting at this time effectively controls the more competitive plants that reduce
the interest of the verge, it also prevents some of the desired plants from flowering and setting
seed. This is not a problem for many grassland species because they can produce a second
flower and/or reproduce vegetatively. Other species may flower and set seed early in the year,
before the first cut. For most annuals and some perennials such as orchids, cutting in May or
June prevents them flowering and setting seed, gradually reducing or eradicating the population
of that species. Where verges support important populations of annuals or such perennials, the
timing of the first cut needs to be amended. It should be remembered, as well, that the provision
of flowers and/or leaves at particular times of year might be critically important for
invertebrates. Practical management needs to balance the sometimes–conflicting needs of
different species and groups of plants and animals. Further difficulties arise when little is known
about the best management for a particular species. Some relationships between plants and
animals are so difficult to understand that there is no obvious perfect time to cut. Management
decisions are then about minimising the likely impact of management. Looking at the past
management of the verge may help in making decisions: usually the species has survived
because of past management (or perhaps in spite of it!).

208

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

The following points may be made:
❍ All grassland areas should be cut annually, once flowering plants have set seed, in, say,
September. This will allow annuals, biennials and short–lived perennials to propagate
themselves and will prevent succession to species–poor grassland dominated by coarse
grasses and ultimately to scrub.
❍ If a second cut is required over part of the verge in order that vegetation height does not
exceed a safe limit, then a spring cut should be made (say, May). If spring–flowering
species of note are present, then the first cut should be later (end–June or July). Many
woodland plants flower early, before shade from trees becomes too great. If the interest
is spread across spring and summer, then the timing within May and June is less
important. The implications of such cuts are shown in Figure 8.3.
❍ Where verges have important annual species or perennials such as orchids that rely on a
single flowering and seeding period, an early cut should be avoided. If an early cut is
essential, it should be in early April to avoid damaging flowering heads.
❍ Where two cuts are required, the first cut should be omitted every five years on parts of
the verge where safety does not require low vegetation. This allows summer–flowering
species that do reproduce vegetatively to set seed and enables the population to maintain
its robustness.
❍ If cuts are essential during the flowering period of a particular sensitive and important
species (due to the need to maintain clear sightlines, for example), individuals or patches
of the species of particular note should be avoided.
❍ On wide verges, the management should be varied across the verge in order to create a
diverse habitat. Such management is labour intensive and costly; it is likely to be feasible
only where volunteer labour is available.
❍ Cuttings should be removed, to prevent smothering of vegetation and to help to maintain
a nutrient–poor environment (which encourages the development and maintenance of
species–rich grassland). Contrary to received wisdom, it has been suggested that the
removal of cuttings does not have a significant effect on soil fertility because the level of
nutrients returned from cuttings is minor when compared with their input from
precipitation, soil development and nitrogen–fixing plants (Pound and Waite, 1994).
❍ Where the removal of cuttings is not possible, cuttings should be finely shredded before
being returned to the verge. Fine cuttings break down rapidly and the smothering effect
is much less. Where the verge is cut with a flail mower, the cuttings are usually finely
chopped and are not likely to represent a problem unless the vegetation was tall and lush
before cutting. In such cases, raking would be worthwhile and the use of a hay mower
should be considered in order to facilitate raking.
❍ The use of hay mowers should also be considered where there are important populations
of less mobile invertebrates, as flail mowers cause high mortality rates.
❍ The cutting blades on flail mowers should be set sufficiently high to avoid scalping the
soil.
❍ Once management has been defined, it should be carried out consistently unless
monitoring indicates that it is definitely not having the desired effect.
Regular cutting of the grassland verge will prevent scrub development. If scrub control is
required, frequent cutting over two to three seasons will usually reduce the vigour of
fast–growing species such as bramble. Where some scrub or individual shrubs are to be retained
on larger verges, shrubs should be cut to the ground on a five–year rolling programme. All
cuttings should be removed from the verge. To avoid disturbance to breeding birds, which is in
contravention of the Wildlife and Countryside Act 1981, the cutting of tall and dense scrub
should be avoided during the breeding season (March to August).

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

209

Uncut

J

F

M

A

M

J

J

A

S

O

N

D

J

F

M

F

M

A

M

J

J

A

S

O

N

D

J

F

M

J

J

A

S

O

N

D

J

F

M

J

J

A

S

O

N

D

J

F

M

D

J

F

M

One cut

J

Two cuts - summer flowers favoured

J

F

M

A

M

Two cuts - spring flowers favoured

J

F

M

A

M

Orchids and annuals present - but two cuts necessary to control coarse species

J

F

M

A

M

J

J

A

S

O

N

Figure 8.3: The effects of the timing of cuts on a grassland sward (based on Pound and Waite,
1994). Courtesy: Kent Wildlife Trust/Malcolm Emery.
210

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

8.7.3 Use of chemicals
Herbicide use is restricted in most areas to the control of weeds on pavements and, sometimes,
control of noxious and/or pervasive weeds such as knotweed and ragwort. Some highway
authorities aim to avoid the use of herbicides to control weeds with, for example, hand–pulling
of ragwort encouraged (Devon) or a full verge cut in summer (Cambridgeshire).
Where scrub control is required prior to the reintroduction of regular cutting, cut stumps may
need to be poisoned with an approved herbicide.

8.7.4 Erosion and disturbance
Where repeated erosion of verges takes place, the introduction of kerbing is often considered.
Where repair of occasional erosion or disturbance is required, the introduction of topsoil should
be avoided. Wherever possible, natural regeneration of the vegetation should be allowed to
occur. Where it is considered necessary to “be seen to be doing something”, the sowing of an
appropriate grass mix at a low density (for example five to ten grammes per square metre) will
still allow herbs a chance to spread naturally from adjacent species–rich grassland into an area
of disturbance, as long as the restored substrate is of a low fertility.
The use of wildflower seed mixes (ideally collected locally) is commonly discussed. The value
of using a wildflower seed mix is debatable. Where there is a suitable seed source nearby and
especially where grassland of conservation value has been lost due to disturbance, then it may
be appropriate. ‘Commercial’ wildflower seed mixes should not be used within, say, 500 metres
of unimproved grassland, in order to avoid the introduction of new and inappropriate genetic
races or even species.

8.7.5 Tree planting and seeding
New species should not be introduced to verges before an ecological assessment of the existing
plant communities has been carried out. As a rule, unless the verge is of little nature
conservation significance, it is better not to introduce new plants. Cultivation of a verge or the
planting of trees, shrubs, grasses or other plants requires a licence to be issued by the highway
authority.

8.7.6 Definition of special verges
The correct marking of verges of interest is also critical. In most counties, verges where the
routine cutting programme should not take place are marked by posts and perhaps by notices at
either end of the stretch of importance (for example, Gloucestershire). Marking the highway
surface is regarded by many as a more effective means of distinguishing verges. It would appear
that concerns about drivers’ response to such markings mean that such an approach has never
been used.
In planning and evaluating any actions that will affect verges, the existence of GIS is effective.

8.7.7 New roads/roadside areas
Due to the widening of roads, many verges have been reduced in width. Opportunities should
therefore be taken to create wide verges wherever possible. Such verges will allow the
development of a more diverse mosaic of vegetation, in terms of both species composition and
vegetation structure, and will ensure that there is an adequate area outside the zone affected by
salt and dust–laden spray.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

211

The use of topsoil should be restricted to tree pits. Providing a relatively low–nutrient substrate
will not only encourage the development of a species–rich, semi–natural grassland but will also
discourage a vigorously growing, high maintenance sward. Wherever possible, the vegetation
cover should be allowed to develop naturally. The sowing of an appropriate grass mix at a low
density will provide an immediate vegetation cover but will still allow herbs to spread naturally
from adjacent species–rich grassland. As discussed above, the value of using wildflower seed
mixes is debatable. Where there is a suitable seed source nearby and especially where grassland
of conservation value has been lost to the construction of a new road, then it is likely to be
appropriate. In County Durham, the verge of a new road built on limestone close to a quarry
that is designated as a Site of Special Scientific Interest was sown using seed collected from hay
taken from the SSSI. Eighty percent of the species found within the SSSI have subsequently been
recorded from the verge of the new road.
With larger verges, some tree and/or shrub planting may be considered. At least in rural areas,
tree and shrub species chosen should be appropriate to the area; again, local native stock
should be used. Some authorities, such as Devon County Council, have prepared guidance on
what species of trees to plant, aimed primarily at parish councils.

8.8 Case studies
A number of case studies are cited below in order to demonstrate positive actions that might be
undertaken to conserve ecology and biodiversity in the highway environment. In all cases, an
important element of these schemes has been the establishment of an action plan. Local
authority biodiversity action plans are playing an increasingly central role in the management
of the natural environment and action plans for the roadside estate should be a fundamental
element of them. A good example of such a plan is the one drawn up for Sussex that can be
found on www.eastsussexcc.gov.uk/env/biodiver. The key to the success of this scheme has
been the partnering arrangements between the voluntary sector, local authorities, statutory
agencies, business sector, landowners and land managers.

8.8.1 Striped Lychnis moth in Buckinghamshire
In Buckinghamshire, stands of dark mullein Verbascum nigrum are protected from all but the
last of the three to four cuts carried out on verges, in order to ensure that the caterpillar of the
nationally rare (Na 1 ) Striped Lychnis moth Shargacucullia lychnitis is able to feed on the flowers
and unripe seed capsules of the mullein. The Striped Lychnis has shown a decline in its national
range of more than 50% over the last 25 years. A recent review of the moth’s distribution
showed that the Buckinghamshire Chilterns represented the major British stronghold (Waring,
1992). In Buckinghamshire, most of the known sites for dark mullein are along road verges and
the principal threat to the moth is loss of the foodplant through verge cutting.
An Action Plan to conserve the species was produced by the Chilterns Countryside Management
Project of Buckinghamshire County Council in February 1997. The Action Plan is in line with
the National Action Plan prepared for the species. One of the actions identified in the local
Action Plan was the sympathetic management of those highway verges where the moth was
recorded during surveys (notably 1996). Details of verges where the moth was recorded in 1996
have been sent to appropriate authorities, including divisional highway staff. Photographs of
dark mullein and the caterpillar of the Striped Lychnis have been reproduced on “cab cards” in
the hope that contractors carrying out verge cutting will avoid the plant during the crucial May
to August period (see Figure 8.4). A late or early cut must be undertaken at other times (April to
May and/or, preferably, September) to prevent the grass sward from becoming too dense
preventing the dark mullein from seeding. As part of the Action Plan monitoring and review
1 Na: invertebrates recorded in between 16 and 30 of the 10 kilometre squares covering Great Britain.

212

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

process, sites where the moth was
recorded in 1996 were re–surveyed in
1998 (Hall, 1998). The 1998 survey
revealed that contractors were following
management prescriptions carefully at
most
locations.
As
a
further
conservation measure, seed of the
mullein has been sown on verges of the
roads associated with the M40 in order
to provide a north–south corridor for the
moth, as existing colonies are
associated with roads with an east–west
orientation.

8.8.2 Roadside nature reserves and
wardens: Kent
Kent has established Roadside Nature
Reserves, monitored by volunteer
wardens, working under a part–time
Road Verge Project Officer. The Project
is managed by Kent Wildlife Trust. The
Kent Road Verge Project was established
in May 1994, with initial funding from
Kent County Council’s Environment
Programme, the County Highways
Department and the World Wide Fund
for Nature UK.

Figure 8.4: Conservation card for Striped Lychnis
moth. Courtesy: Buckinghamshire County Council Countryside Services.
©Buckinghamshire County Council.

Kent’s diverse geology has given rise to
many different soil types. Based in part
on geology, nine areas have been
defined, each with their own
characteristic roadside vegetation (Pound
and Waite, 1994). Some verges are of
special interest because of the presence
of particularly rare species. Rare plants
found on Kentish verges include
clove–scented broomrape Orobanche
caryophyllacea, (see Figure 8.5), man
orchid Aceras anthropophorum , lady
orchid Orchis purpurea and hairy
rock–cress Arabis hirsuta . A colony of
the specially protected hazel dormouse
Muscardinus avellenarius is found on a
verge adjacent to the A21 and rare
invertebrates are known from several
verges.
The Kent Wildlife Trust carried out a
detailed district–by–district survey of
road verges in Kent and around 10 road
verges in each district were designated
as Roadside Nature Reserves (RNR).
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

213

These are sites that are of high value for nature
conservation and which would benefit from a
change in management. There are currently 131
RNRs in the 14 districts of Kent, covering a total
length of 89 kilometres. Signs have been erected
at each end of the RNRs explaining that the site
has been designated and giving the telephone
number of the Kent Wildlife Trust for further
details. The signs have four distinct functions:
❍ to show the contractors where to start and
finish the mowing specified in the RNR
management plan;
❍ to enable adjacent landowners to contact
the Project;
❍ to alert local people to the importance of
the verge, and
❍ to protect the site from unintentional
damage by other contractors, for example,
cable–layers.
Highway maintenance in Kent is carried out by
the Highway Units of Kent Highways, a
partnership between Kent County Council and
the District Councils. A brief management plan
has been drawn up for each RNR in liaison with

Man orchid. Courtesy: Anna Marshall.
the relevant Highway Unit. This defines the
optimum mowing regimes that will conserve
or enhance the nature conservation value of
the habitat without compromising road safety.
It takes into account the nature of the habitat
and the presence of any rare or unusual
species. The cutting of the RNR is usually
carried out by the Highway Unit’s contractors
or occasionally by one of Kent County
Council’s Countryside Projects. Additional
management, such as scrub clearance, is
carried out at some sites, as necessary. Close
liaison between the Road Verge Project
Officer and Highway Units is essential.

Figure 8.5: Orobanche caryophyllacea.

There are currently 86 volunteer wardens,
covering approximately 70% of the RNRs.
Volunteer wardens are recruited from the local
community. They take responsibility for the
verge, ensuring that any problems or issues
are notified to the Road Verge Project Officer
at the Trust. Wardens are issued with an
identity card and an information pack, and are
invited to attend training days and additional
events that concentrate specifically on the
conservation of RNRs.

Courtesy: Alan Lewis.
214

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

8.8.3 Special verges in Essex
In the 1970s, Essex County Council’s Highways Department with the help of the former Nature
Conservancy Council (now English Nature) and the Essex Wildlife Trust identified a list of
roadside verges which were designated as Special Roadside Verge Nature Reserves (Markham,
1999). Appropriate management policies were defined and, in 1974, with financial support
from the County Council’s Planning Department, the first verges were marked on the ground.
Unfortunately, following local government reorganisation in 1974, the verges became a low
priority for the County’s Highway Department. In 1980, the Essex Wildlife Trust reopened
debate on the issue and a three–year pilot scheme was set up in northwest Essex under the
guidance of Joan Mummery of the Trust. The pilot scheme was designed to assess the impact of
different management techniques on the flora of the verges. A network of voluntary verge
representatives from the Trust was established. The pilot scheme defined not only effective
management regimes but also lines of
communication between ecologists and highway
engineers. The scheme was so successful that it
was subsequently extended to the rest of the
county. There are now 103 Special Roadside
Verge Nature Reserves, covering 44km.

There is a basic cutting regime for all verges. In
April or May, a one–metre wide cut is carried out
along the carriageway edge. This is followed in
Autumn by a full verge cut in alternate years.
Where interim cuts are required to conserve
important species, such as crested cow–wheat
Melampyrum cristatum , sulphur clover Trifolium
ochroleucon and lesser calamint Clinopodium
calamintha , agreements are arranged with local
farmers or specialist contractors and paid for by
the planning department from the Landscape
Conservation Programme budget.

Sulphur clover. Courtesy: Anna Marshall.

Crested cow–wheat. Courtesy: Anna Marshall.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

215

8.9 Where to find further information
Guidance on the creation of new verges is provided in the Good Roads Guide , Section 1 of
Volume 10 of the Design Manual for Roads and Bridges (DMRB) and also in Roads and nature
conservation: Guidance on impacts, mitigation and enhancement (English Nature, 1993). A
Landscape Management Handbook is in the process of finalisation, which will join the
Wildflower Handbook as components of the DMRB.
Much useful information on the management of grasslands is provided in The Lowland
Grassland Management Handbook (Crofts and Jefferson, 1994). The appropriate management of
ditches and hedges is discussed, inter alia , in Pound and Waite, 1994.
The Highways Agency is working with English Nature and other partners on a programme of
research to develop understanding of biodiversity in the context of highways management. The
Agency is also preparing a biodiversity action plan for the management of the land surrounding
the major road network (Highways Agency, 1999).
Lincoln Garland at Bristol University and members of The Mammal Society are undertaking a
survey of small mammals on road verges, looking at how small mammal numbers are related to
various habitat features ( Mammal News , No. 87, Autumn 1999).

8.10 Principal recommendations
1. The development of appropriate management of road verges for nature conservation requires
close and efficient working relationships to be established between the wildlife trusts,
highway authorities and contractors.
2. The relationships between ecologists and highway authorities work most effectively where
the level of funding meets the true costs of successful nature conservation (Alexander, 1995).
The role of volunteers is also important but is not a substitute for proper funding.
3. There needs to be clear allocation of responsibility and authority for promoting conservation.
4. Involving the public and adjacent landowners is beneficial.
5. Comprehensive survey of roadside verges is required to establish their existing or potential
value for nature conservation and to inform management decisions.
6. Simple and clear management plans should be produced for each verge of importance or for
groups of verges with similar management requirements.
7. Special verges should be clearly marked on the ground.
8. Once a management scheme has been defined, it should be followed consistently unless
there are definite indications that it requires revision.
9. Simple monitoring (for example, fixed–point photography) should be carried out at all sites
in order to inform the periodic review of management.
10. At most sites, the following management will encourage biodiversity:
❍ cut verges in September;
❍ cut productive verges in May and September;
216

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

❍ cut productive verges with important spring–flowering species in late–June and
September;
❍ cut productive verges with important annual species or orchids in early April and
September;
❍ position the blades high enough to avoid ‘scalping’;
❍ remove smothering grass cuttings;
❍ do not pollute with chemicals (fertilisers, pesticides, salt, road run–off and so on);
❍ avoid erosion and disturbance;
❍ control scrub, for example, cut shrubs to the ground in winter on a five–year programme,
and
❍ maintain hedges and ditches in an appropriate manner.

References
Alexander L, 1995

The Roadside Verge Report. Researched and compiled by
SWT Environmental Services Ltd, Edinburgh, for The Wildlife
Trusts’ national office.

Colwill DM, Thompson JR
and Ridout PS, 1976

Studies of Conditions for Vegetation in the Central Reserves of
Motorways: a Preliminary Report. Supplementary Report
217UC. Transport and Road Research Laboratory,
Crowthorne.

Colwill DM, Thompson JR,
and Rutter AJ, 1982

An assessment of the conditions for shrubs alongside
motorways. Laboratory Report 1061. Transport and Road
Research Laboratory, Crowthorne.

Crofts A, and Jefferson RG (eds), The Lowland Grassland Management Handbook. English
1994
Nature/The Wildlife Trusts.
Davison AW, and Wharmby S,
1979

The Effects of Ethylene on Vegetation. In The Impact of Road
Traffic on Plants (edited by DH Colwill, JR Thompson and AJ
Rutter). Supplementary Report 513, Transport and Road
Research Laboratory, Crowthorne.

Elton, CS, 1966

The pattern of animal communities. Methuen, London.

English Nature, 1993

Roads and nature conservation: guidance on impacts,
mitigation and enhancement.

Hall P, 1998

1998 Species Action Plan Sites Survey: The Striped Lychnis
Moth. Report prepared for Buckinghamshire County Council
Environmental Services.

Hickman AJ, 1989

Measurement of Particulate Lead on the M4 Motorway at
Harlington, Middlesex (Fifth report). Research Report 184,
Transport and Road Research Laboratory, Crowthorne.

Highways Agency, 1999

Towards a balance with nature. Highways Agency
Environmental Strategic Plan.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

217

218

Mansfield TA, 1979

The effects of nitrogen on vegetation. In The Impact of Road
Traffic on Plants (edited by DH Colwill, JR Thompson and AJ
Rutter). Supplementary Report 513, Transport and Road
Research Laboratory, Crowthorne.

Markham D, (ed), 1999

Special verges in Essex. Nature’s Place, March 1999.

Ministry of Transport and
Civil Aviation, 1955

Spraying of roadside verges. Notes for guidance of highway
authorities. Circular NO. 718, HCR. 42/3/05.

Port GR, and Thompson JR,
1980

Outbreaks of insect herbivores on plants along motorways in
the United Kingdom. Journal of Applied Ecology, 17,
pp649–656.

Pound D, and Waite A, 1994

On the Verge: A practical handbook for roadside verge
management. Kent Trust for Nature Conservation, Maidstone,
Kent.

Tansley AG, 1949

The British Isles and their vegetation. Cambridge University
Press, Cambridge.

Thompson JR, 1986

Roadsides: a resource and a challenge. In Ecology and Design
in Landscape (edited by Goode, DA and Thorp E), pp
325–340. Blackwell Scientific Publications, Oxford.

Thompson JR, Rutter AJ, and
Ridout PS, 1986

The salinity of motorway soils. II. Distance from the
carriageway and other sources of local variation in salinity.
Journal of Applied Ecology, 23, pp269–280.

Waring P, 1992

The Striped Lychnis Moth, Cucullia lychnitis – a Review of its
Distribution and Status in Britain. Entomologist Gazette , 43,
pp179–205.

Way JM, 1969

Road verges – research on management for amenity and
wildlife. In Road Verges: Their Function and Management
(edited by JM Way). Monks Wood Experimental Station,
Abbots Ripton.

Way JM, 1973

Road verges on rural roads: Management and other factors.
Monks Wood Experimental Station Occasional Reports, No.
1. Abbots Ripton, Huntingdon.

Way JM, 1977

Roadside verges and conservation in Britain: a review.
Biological Conservation, 12, pp65–74.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

C HAPTER 9. M ANAGEMENT OF H IGHWAYS WITHIN THE
B UILT H ERITAGE
9.1 Introduction
This chapter considers the environmental management of highways in relation to the built
heritage. The focus of the Chapter is not upon the appraisal of individual buildings, but rather
on the spaces between them because many of the important spaces between buildings are roads:
spaces that also have an important function for transportation. It explains the current thoughts
on the identification and enhancement of the built heritage. It accepts that sometimes there may
be legitimate conflicts between securing efficient transportation and of conserving heritage. It
concludes with examples of how some of these conflicts can be resolved.

9.2 Listed Buildings and Ancient Monuments
Possibly, the most commonly and easily understood form of protection for the built environment
is “listing”. Listing is a shorthand term used to describe one of a number of legal procedures that
enables the protection of the architectural heritage of the country. The name derives from the
statutory lists of buildings of “special architectural or historic interest” which the Secretary of
State for National Heritage is required to compile. Once a building is listed, consent must be
obtained before any alterations are made that might affect its special character. A list of some
relevant publications and legislation relating to protected structures is illustrated in Box 9.6.
Listed buildings are assigned a Grade depending on inter alia their architectural or historic
interest, rarity or setting.
Grade I: Comprise those buildings of exceptional interest.
Grade II*: Comprise particularly important buildings of more than special interest.
Grade II: Buildings of special interest that warrant every effort to preserve them.
Of the nearly 370,000 listed buildings in England, 92% are Grade II, six percent are Grade II*
and two percent are Grade I. Many of these buildings are houses or cottages which line the
roads and country lanes. It follows that these roads and lanes contribute much to the settings
and character of the listed building, and that management and maintenance of the highway
network is critically important in the preservation of the built heritage.
Listing is not intended to mothball a building. Certain listed structures do need to be conserved
as “found”, but underpinning the planning legislation is a belief that the long-term interests of
a building are best served by its remaining in use and often the best use is the one for which it
was designed. Listing tries to ensure that if any changes are necessary they respect and retain
those qualities and characteristics that make the building special.
Ancient monuments are those archaeological or historical sites and features which are either
protected under national archaeological legislation or are contained within county or unitary
authority Sites and Monuments Records (see Box 9.6). They comprise a broad range of features
from earliest prehistory to the present day. Unlike listed buildings, ancient monuments are
generally not capable of beneficial modern re–use, but they often form significant elements of
the townscape or rural landscape bordering highways. In the case of historic highway
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

219

alignments, they could also form part of the modern route (such as Roman roads, medieval
bridges and so on).

9.3 Groups of buildings
Typically listed buildings are often perceived as great country houses or monumental structures
in city centres. However, many buildings of special merit derive that merit not so much because
of their own intrinsic value and interest but because of their position as part of a group of
buildings.
The most easily recognised groups are those which have been designed as such. The Georgian
terraces and squares at Bath, London and Edinburgh were conceived as single structures, though
divided up into individual houses.
Similar group characteristics can be seen in the appearance of the buildings surrounding the
parish church of a rural village. The parish church dominates by its comparative size and is
medieval in design and construction. Smaller adjacent buildings may be domestic Georgian
buildings in the high street and smaller cottages behind. Their relationship to a village green,
main street and landscape is seen as a complete composition
If any of the individual buildings in either group, that is the uniform terrace or irregular village
centre, were put in a different location and context, the visual value would be diminished.

9.3.1 Settings of groups of buildings
Taking the same two example groups, it can be seen that the immediate surroundings, or the
setting for the group, contribute as much to the quality of the group, as does any one of its
constituent buildings. The foreground setting appears to be an intrinsic part of the group. Thus
the environmental management of the buildings themselves must include the surrounding
highway spaces.
In the example of the Georgian terrace, the pavement width in relation to the height of the
buildings, the width of the road and surface treatment all complement and add to the complete
scene.
In the example of the village group, the same is true. Informal groups of buildings are
complemented by informally designed ground surfaces in the foreground. Paths, green verges
and the treatment at the edge of verges, all help to reinforce the character and the quality of the
group.
The design and maintenance of surfaces – that might normally only be considered in terms of
highway safety, efficiency and practical management – is of great relevance to the objectives of
conserving and enhancing the built heritage.
Thus, it is not only the individual buildings themselves but also their combined grouping
including the space, such as the highway, that form the cultural heritage.

9.4 Conservation and Conservation Areas
The ideas behind conserving the heritage of whole areas through Conservation Area protection
are similar to that of listing individual buildings. The emphasis is on retaining the practical use
of areas rather than creating unusable museums. Rather than rigid preservation, conservation in
this context could be described as the art of adapting the inherent qualities of historic groups of
220

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

buildings and places so that
they can still be used
meaningfully
in
modern
economic conditions.
In
order
to
carry
out
programmes of conservation, it
is necessary to understand
clearly what quality or character
of an area is worthy of
conservation. This often requires
some thought as to the special
attributes that make one town or
location distinguishable from
another. A clear definition needs
to be established of which
features make a resident feel at
home and what it is that gives
the visitor a new pleasurable
experience such that they would
wish to return.

The way buildings are grouped together creates the
character of a place. Often a highway is the setting for the
group.

Very often these distinguishing factors are not single monumental buildings but the way in
which quite modest buildings are arranged. The point has been well described by Gordon
Cullen (Cullen, 1961):

“One building stands alone in the countryside and is experienced as architecture, but bring half
a dozen buildings together and an art other than architecture is made possible. This is the art of
townscape.”
At the most basic level it is what helps people recognise and distinguish one place from another.
Visually most towns derive their identity and personality from the way in which individual
buildings, both good and not so good, together create a general atmosphere and form a
recognisable townscape. It is the distinct organisation of spaces and an arrangement of
buildings that combine as a whole. The total image of a town, its relationship to the countryside
and its underlying land form may be so powerful that it merits conservation on that alone.
With perhaps a few exceptions, preservation in the restrictive sense and on such a wide scale
could become damaging to the life and prosperity of the town. Careful conservation can be a
stimulus to economic regeneration. By conserving the qualities that distinguish one town from
another and make it attractive to visitors its economy may be revived and sustained. The
highways that pass through and around the town will also have a significant role both in terms
of economic development and their overall contribution to conservation and environmental
enhancement. It is here that the interrelation of conservation with highway and traffic
engineering is seen. The space that is reserved for movement is also essential to an element of
the towns attractiveness that has a fundamental bearing on its economic well–being.

9.5 Spaces between buildings
An enclosed space can be described as a room without a roof. The most formal spaces are those
enclosed by buildings in the form of a formal Square. These include market squares, town
squares and village greens. They are recognisable and have a function as places to gather, to
sell produce, to hold fairs. These areas form “social” space where people can interact. Such
areas can be quite large, as in the case of a village green.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

221

Less obvious are the incidental spaces that occur between buildings and which are enclosed by
them such as forecourts, leading off a thoroughfare, which may provide a formal setting to a
distinguished building. These spaces must be seen as a part of the building itself. An example
would be the space in front of a town hall. It might be little more than a widened pavement or
it could be several metres in depth and contain sculpture, trees, and even a formal fountain.
Where such space is within the curtilage of the building it might be easily recognised but be
wholly in the public domain, merely an extension of or widening of the pavement
Environmental management must be directed towards enhancing both the building(s) as well as
the highway itself. A holistic approach is favoured. Concern for the character of external spaces
and the contribution they make to the character of a town, can be easily overlooked by local
authorities. Yet, though seemingly of little importance, they are often the elements of visual
character that distinguish one town from another.
Most commercial buildings in a typical high street have a great deal in common with those in
any other high street. Chain stores, for example, strive to achieve a brand image that is repeated
across the country. As a result they all look very similar and the similarities out weigh the local
distinctive characteristics. Thus, in distinguishing one high street from another, reliance is
placed on the recognition of the size, shape, surface materials and any other locally distinctive
characteristics that can be observed in a seemingly insignificant space. For example, a town
hall may have a classic design front elevation, reminiscent of a Roman or Greek temple. The
character of such buildings would be made locally recognisable by the different characteristics
of the space through which they are seen. These include:
❍
❍
❍
❍

conventionally on raised ground;
along a street flanked by other buildings;
seen half hidden from an approach road;
seen fully from an approach road leading into the main road on which the building
stands, and
❍ seen at the centre of a formal terrace which encloses a large square.
In each example it is the space that provides the local distinguishing characteristic. The building
itself is important but probably is similar in size and style to those in many other towns.

9.6 Emphasis on linked spaces
Space that forms the setting of a building or a group of buildings is an essential element in
creating local distinctiveness. Often they help people to recognise a place even more than the
buildings themselves.
Concern for the quality of linked space takes these ideas further. In some towns there are a
series of inter–linked spaces. Possibly they may have been part of a medieval street pattern that
has remained, while the buildings that line them have been replaced many times. They may be
part of a street pattern which was first created in Roman times, adapted in Medieval times and
incorporated into Georgian formal town planning layouts.
Whilst most English city centres appear modern, there are, at the heart of many, reminders of
their heritage in the form of alleys, narrow streets, back yards and oddly shaped incidental
external spaces, caused by irregular property boundaries for example, in St Albans. The
experience a visitor has in passing from these passages and seeing their relationships to larger,
more formal, spaces, is itself an experience which contributes greatly to the enjoyment of
simple, pleasurable exploration.
222

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

9.7 Emphasis on the public street, road and highway
Having shown the importance that external spaces have in defining the special characteristics
and heritage of a town, it follows that many of those spaces will also be highways or serve a
transportation function. Urban roads are clearly part of the continuing network of external
spaces but rural roads and highways also have a part to play in emphasising the quality of
heritage such as roads at the edge of village greens. There is another aspect: the experience of
open countryside seen from inside a moving vehicle. Indeed the experience takes on an
additional dimension when travelling. A particular example is seen on the north bound M40
approaching Oxford as the motorway slices through the Chiltern hills in a deep cutting. It
curves, turns to the right and at normal motorway speeds the observer in a vehicle sees the
whole of the Oxfordshire valley revealed in less than twenty seconds. There are many
memorable landscapes that can be seen from motorways. Though possibly less dramatic, they
do clearly indicate a sense of place and location (see also section 7.3.5).
Rivers are crossed, hills climbed, woods penetrated. Having seen one river, hill or wood the
observer becomes more discerning and notices the variety of scenery. These experiences have
the added benefit of contributing to road safety by reducing driver stress. Thus the street, be it
urban or rural has a clear function in that it is part of the nation’s heritage and assists in the
appreciation of the qualities of that heritage.
In many town and cities, as well as the countryside, many road environments are either
run–down or lack the care and attention necessary to make them attractive either to residents
or road users. In such places great emphasis must be placed upon ensuring that changes to the
transportation systems, especially highways, do not make the local environment worse. For
example, environmental degradation will result if excessive traffic is permitted along unsuitable
roads along with the associated road–side infrastructure of signs, parking, and so on. Making the
most of opportunities to improve the highway environment should not rely on transport budgets
alone. Other opportunities may be available, for example via the Single Regeneration Budget,
that can make a considerable contribution towards improvement.

9.8 Why does heritage matter?
9.8.1 Cultural base of the community, national and local
Society needs both cultural and physical roots and a town’s visual and historic qualities can satisfy
at least part of this need. That is why for so many people, old–established towns seem so pleasant
to live in. This would apply also to the old established parts of modern cities and to similar areas
in rural villages. There is something attractive in genuine links to the perceived quality of the past
that makes people pay considerable sums for the privilege of living in such environments.
It is important to distinguish the genuine from the pastiche. There are many fake or partially
historic environmental ornaments that can be applied to towns. But with no clear reference or
logic they become merely irrelevant trivia. The need is for quality. To have examples of the best
of a previous age and match it with the best of the current.
In the highway environment, local construction materials and details are often valuable,
characteristic elements in an urban or rural scene. Dry stone walling as highway boundaries,
bridges and other historic features may have important local historic significance, in addition to
their current practical purpose. Attention to detail is vital.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

223

9.8.2 Economic well–being
Image is far from being a peripheral interest. Whole sectors of the economy rely on the delivery
of style and image for the sale and promotion of goods and services.
Indeed town centres are intended to attract visitors and customers. Towns were places where
people congregated to trade and to do business. A key consideration is whether there is the feel
or ambience of a “nice” place: what might be called a “feel–good factor”. Is the town really
worth a second visit? Is it distinctive? Are there pleasant and convenient spaces? Is there an air
of welcome and a feeling of well–being?
As many of the factors that go to make up this overall impression are beyond the control of the
local authorities, there is an emphasis on making the very best of the characteristics that exist.
Heritage has a real part to play.

9.8.3 Contribution to regeneration
These considerations can be
developed further. There are
positive programmes to
promote regeneration by
emphasising inherent local
qualities. Conservation and
heritage are an important
ingredient in the promotion
of an area and in the
establishment
of
new
attractions and business.
Many
regeneration
programmes have particular
heritage themes at their
centre. For instance English
Heritage
funding
programmes operate across
the whole of England, often
Paving and street furniture layout in a street partially closed
in the most deprived areas.
to traffic designed to encourage people to stand and talk.
The built heritage is often at
the heart of successful Salisbury.
regeneration projects. Again
this is done not in a fake or half–hearted way but as the genuine and subtle enhancement of the
special local characteristics, albeit business or cultural or a combination of both.
The creation of theme parks is not the aim, but in numerous small towns, the needs of local
industry have become the focus of new and sustained enterprise. These needs should be built
upon to provide a distinctive character for the locality and, in doing so, make it more attractive.

9.9 Emphasis on the whole scene
To carry out such programmes in a convincing and sustained manner, the elements of heritage
enhancement need to be complete. Small add–on frivolous trinkets will appear insufficient. To
be meaningful and permanent, the work to emphasise heritage has to encompass the whole
scene. If a street is an essential part of a sequence of the enclosed spaces that complement a
224

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

group of buildings in a conservation area, then every part of the appearance of that street will
have an impact on the appearance of the area and thereby on its economic well–being.
Views into, of and within an area are vitally important. All aspects of a road are relevant: its
width in relation to the height of buildings, the width or footways, the surface treatment of both
carriageway and footway.
In addition, equipment and signs seemingly only of interest to road users will form part of the
total scene. Traffic signs, their support posts and brackets as well as their backs, remain in view
even when there is no traffic. Similarly road markings, though having a practical function, often
dominate the foreground of many scenes.
Care and attention may often be taken in the design and location of major initiatives affecting
the setting of a conservation area, but many of the day–to–day maintenance activities of the
street, which may effect the whole scene, are seldom visually co–ordinated. Not only must areas
be maintained, using natural materials to fit in with the character of the street, but the street
furniture, signing and so on must be kept to a minimum. Unless absolutely necessary, perhaps
for road safety or regulatory reasons, they should be removed. Similarly poorly located street
furniture should be relocated or removed.

9.10 Heritage in everyday life
Sense of place is a term, which is often used to refer to a place that has an identity of its
own: a recognisable place, a memorable place.
To be memorable it has to have a single image – something that is seen to be different from
the average in that it can be remembered and distinguished from others.
Brand names of products strive to achieve such memorability. Places almost have to promote
a brand image to achieve that effect. Some images in London – Tower Bridge, Big Ben, the
dome of St Paul’s Cathedral have become national symbols. The crudest sketch can help to
recall them.
Individual elements of towns need to have the same clarity to be truly memorable to all but
those most familiar with them. Each has to become the focal point in a scene, to be clearly
remembered.
A single isolated tree in a field is the undisputed focus of attention. In size, in colour and in
shape it is distinguished from its surroundings. In comparison the spire of a church or the
tower of a building is seldom seen in isolation. They are normally seen as part of a crowded
urban scene, possibly a street scene. The distinguishing tower has to compete for attention
with all that is in the foreground – landscape features, other buildings and all that is
associated with the street.
The object that helped to identify where the scene is located, itself becomes less clear and
less likely to be easily recalled
So one objective in helping to retain an image of a place in mind, the sense of place, is to
identify what is the focus of attention and to seek to retain its visually dominant position in
the total scene.

Box 9.1: Sense of place.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

225

9.11 How can heritage be enhanced by highway
management?
9.11.1 Enhance the setting
The rules and concerns for
establishing the identity of
a location have been
examined. These follow
conventional processes in
current
conservation
practice
and
are
elaborated upon in the
textbooks on the subject.
Highways, as the term
suggests, have a function
to assist movement. They
also have an essential
function in that they often
form the setting for
buildings with heritage
value. This setting may be
Hedges, walls verges, even ditches lining a highway may be the
urban or rural. Hedges,
important foreground to a cherished view.
walls,
verges,
kerbs,
footpaths and even ditches lining a highway may be the important foreground to a cherished
view. Equally important in a town, highways may actually be part of a series of external spaces
that are themselves of heritage value. That is, value in terms of economic well being, if not
actual measurable economic regeneration.

A second way to emphasise the particular identity of a group of buildings or a location is to
analyse the visual themes. These may relate to historic style, possibly as a consequence of
past development, or they may have a clear stylistic, textural or colour theme, as a
consequence of the use of a limited range of local building materials or consciously adopted
styles.
Enhancement would continue the visual themes. Such themes might, for example, be the
adoption of clear rules of symmetry.
There are numerous examples. One of the best known is the relationship of Buckingham
Palace to the Mall, in London. The building is symmetrical and is positioned in a
symmetrical relationship to the Mall. Further subsections of the building are also
symmetrical, to the extent that dual carriage entrances through the building are designed as
arches, which are by definition symmetrical. In addition all the decorative features: lamps,
adjacent windows, stone coursing and even sentry boxes, are all arranged in a symmetrical
relationship to each of the dual arches.
Clearly any object, however insignificant would need to be arranged symmetrically. If not,
it would gain a totally unintentional prominence.

Box 9.2: Identity and clarity of location.
226

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

The geometry of the carriageway, its relation to the width of footway, and the surface material
of both, can dramatically enhance the setting of a building. The use of natural stone paving is
common in places where higher standards are deemed necessary. But the expense restricts their
use to a very few places. Of greater importance is the use of a range of more economic materials
which can be easily maintained but which will complement a conservation area or building of
heritage value.
To this end care is needed in the selection of alternative materials. The choice of concrete and
clay products is very wide and a degree of restraint is needed. Sometimes research or guidance
as to what would be historically or geographically appropriate will be required. Some local
authorities, such as Bath, impose strict standards to ensure conformity of materials.

9.11.2 Reduce street clutter
The simplest way to enhance a
scene is to reduce the visual
clutter of street furniture.
Clutter erodes the impact of
what should be the visual focus
of attention. Clutter distracts
attention from the elements in
the scene that give a clue to its
identity and location. In short,
clutter is common everywhere
and therefore blurs the view of
that which is special and
attractive in the scene.
In many places the form that
clutter takes is almost exactly
the same. The foreground to
many scenes are exactly the
same
and
distinguishing
characteristics have to be
sought out.
It is unfortunate that much of
the clutter is associated with
traffic equipment or information
to drivers and other road users.
Whereas clutter and uniformity
should be avoided to enhance
heritage, identity and economic
well
being,
universally
recognised
and
easily
understood information to
drivers requires nationwide
uniformity. Nevertheless the
road side infrastructure should
not be allowed to dominate the
highway environment.

Street clutter can be reduced, for example, by fixing traffic
signs neatly to walls and by incorporating tactile paving
into the street scene.

Considerable care and skill is
needed to resolve these
seemingly conflicting objectives.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

227

Much of English design tradition is formed less on symmetry, which may be considered to be
too regimental, than on a more subtle informal order. The rules are more complicated but
allow for interpretation.
One example is the way in which a person walking down Fleet Street sees the front facade
of London’s St Paul’s Cathedral. This is an example of an important building being
positioned so that it is gradually revealed. The building is not approached up a long avenue,
as is St Peter’s Rome, rather it is deliberately partially hidden from view. Walking down
Fleet Street towards Ludgate Circus, more of the facade comes in to view. The whole facade
is not visible until Ludgate Hill, almost at the front of the Cathedral. By that time the dome
can no longer be seen.
There are also subtleties. From Fleet Street the dark spire of St Martin’s Ludgate seems to pass
across in front of the lighter coloured structure of the drum and dome of the Cathedral.
There are similar combinations of white buildings and darkly coloured objects on the Mall
side of Buckingham Palace. The dark sculpture and ornate lamp posts contrast with the light
stone of the Palace and the Victoria Memorial. When colour is added, it is the striking colour
of parade uniforms and processional decorations. At other times the scene is neutral so that
the contrast with the colour of occasional pageantry is more marked.
Relating the colour and texture of building and ground surface materials can create a sense
of visual order. Typical examples are where they have occurred historically because they
were the best available at a particular location.

Box 9.3: Informal visual order.
9.11.3 Co–ordinate detailed design with the character of the locality
Within existing legislation and practice there are numerous ways in which clutter can be
reduced while maintaining safety standards for the movement of vehicles and other highway
users.
The aim would be to retain the items in the street which are absolutely essential for efficient and safe
movement – actual traffic direction and regulation signs – but remove or hide items that are not
essential or do not need to be seen by drivers such as signal control boxes, and crude sign supports.
An often–quoted example is the use of brick by the Dutch for virtually everything. In a
country devoid of stone, clay products were used for building and for paving. It is possible
to see town squares in the Netherlands where all the buildings as well as the pavements and
roads are made of a single material: brick. This could be described as boring but it clearly
has a unity of material that requires the designer to achieve variety by different texture and
very minute changes in colour.
In England, it might seem that almost anything could complement grandly robust Victorian
monumental buildings, dripping with decoration, vivid colours and varieties of texture. In
fact such buildings were usually very consciously designed and rather like a fully
orchestrated symphony, require the same care in any further embellishment or alteration.
Thus attention to the intrinsic elements of a visual theme in carrying out any alterations can
safeguard the identity of a place and help emphasise the identity of a location.

Box 9.4: Use of colour and texture.

228

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

In practice this requires each category of traffic related street furniture to be considered with a
view to removing or hiding those which are not essential for efficient and safe movement. It may
seem that what can be done is quite modest and individually hardly worthwhile. Yet, the total
effect of carrying out a number of small measures at any one location is significant.
The most obvious first step is to remove redundant posts and support structures. Signs seldom
need their own supports if lamp columns are adjacent. There is often a degree of latitude in the
precise location of traffic information signs, though traffic regulation signs need to be more
accurately positioned. Single posts can be used for more than one function. Traffic signals can
be fixed to lamp columns, if they are suitably positioned, and signal control boxes can be sited
out of sight. Simple waiting restriction signs seldom need their own posts because there is a
range of satisfactory alternative positions where they can be effective. They can often be fixed
to adjacent boundary walls or railings at the back edge of a footway. Information signs can often
be fixed to adjacent walls. This also reduces the need for separate support posts. In each case
the actual position of the sign on the wall or fence should also be decided upon with
consideration for the visual role of the wall or fence in the whole scene. Negotiation with
property owners will be required for wall mountings. It is important to emphasise that the
governing factor for any reduction in signage or clutter must be highway safety.
Reduction of street clutter.
Fix signs to lamp columns
Fix traffic signals to lamp columns
Fix no waiting signs to railings, walls, litter bins or benches
Set traffic signal control boxes into walls
Fix traffic direction signs to walls
Fix traffic regulation signs to walls
Combine signs onto least possible support posts
Reduce lengths of guard–rails
Remove guard–rails
Reduction of road markings
Use natural features for traffic calming
Reduce the need for bollards by using other existing street furniture repositioned if
necessary
Reduce zigzag lines to a minimum
Reduce width of yellow lines to 50mm
Form road markings in natural materials, for example, white stone

Box: 9.5: Reduction of clutter.

9.12 Challenges to the enhancement of heritage
9.12.1 Unresolved conflicting objectives and national advice
A look at the visual chaos of an average high street demonstrates that there are an unlimited
number of difficulties. Many of the day to day requirements of traffic management result in a
visual environment that is totally contrary to the objectives of heritage and conservation. Poorly
designed and maintained street furniture, broken paving, oddly laid out tactile paving, all makes
up a mist of clutter that mars the foreground and detracts from the visual quality of most high
streets. More careful co–ordination and consideration can improve many of these factors,
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

229

although there are still matters that are insisted on by government or official guidance for
highways and transportation that appear to conflict with other general guidance on the
enhancement of heritage and conservation.
Archaeology.
Some 13,000 sites are included by the Secretary for State for National Heritage in the present
schedule of monuments under the Ancient Monuments and Archaeological Areas Act 1979.
Once a monument has been scheduled, the consent of the Secretary of State is required
before any works are carried out which would have the effect of demolishing, destroying,
damaging, removing, repairing, altering, adding to, flooding or covering up the monument.
Official advice is contained within Planning Policy Guidance Note (PPG) 16, DETR.
Ancient Monuments
Sites and Monuments Records are maintained by either county or unitary planning
authorities, identifying all currently known archaeological sites within their boundaries.
Advice on these sites is available from local authority archaeological officers. Advice on
ancient monuments, especially those protected as Scheduled Monuments under the Ancient
Monuments and Archaeological Areas Act, 1979 and on other aspects of the historic built
environment is available from English Heritage.
Planning and the historic environment.
The Town & Country Planning Act 1990 (as amended) is the principle Act.
The Secretary of State for National Heritage has a duty to compile or approve lists of
buildings of special architectural or historic interest.
Local plans prepared under the Act are required to set out the planning authority’s policies
for preserving and enhancing the historic environment in their area including the
designation and formulation of proposals for individual conservation areas.
PPG 15 sets out Government policy on planning and the historic environment with regard to
transport and traffic management, new traffic routes, roads in centres or settlements,
floorscape and street furniture. The flexibility authorities have in the design of traffic calming
features under the Highways (Traffic Calming) Regulations 1993 is emphasised. Reference is
made to the many examples of good practice in reconciling traffic and environmental issues,
illustrated in a publication by the Civic Trust & English Historic Towns Forum: Traffic
Measures in Historic Towns.

Box 9.6: Legislation and official advice.
9.12.2 Limited interdisciplinary technical knowledge
One major difficulty in resolving the conflicting objectives of transport and heritage, is the
insular way in which the professions are trained and in the way that traffic and highways
legislation is kept separate from legislation concerning overall land use and environmental
planning.
In addition to the two strands of interest being separate, there is a different approach to how
they are dealt with. Matters relating to traffic are often considered as technical, with little room
for personal subjective value judgements.

230

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

However, much of the appreciation of heritage, while relying on an understanding of historic
precedent and development, also involves an acceptance of artistic values. Such values are not
easy to quantify but the fact that they exist and have a value cannot be denied. In a professional
culture that relies on rules and formulae, as well as proof of success, artistic values have to be
explained in straightforward often financial terms.
Yet even in the disciplines of highways and transportation, the evaluation and competing
priority of claims which do not have a common base, have to be compared. The evaluation of
the comparative claims for road space by private vehicles compared with buses, taxis or cycles
have to be resolved and to this must be added the claim for space by pedestrians. Detailed
guidance on these matters is given in Transport in the Urban Environment (IHT, 1997).
Here the simple comparisons become more complex as consideration is given to assessing the
value society is prepared to put, not only on the basic space necessary for people to physically
walk, but the additional space needed to walk in comfort and even the additional space and
amenity to enable people to walk with pleasure. If it is accepted that pedestrians put a value on
walking with pleasure then it must be considered what contribution is made by the appreciation
of heritage. Having done so it is necessary to quantify them where possible and see how the
appreciation of heritage can be enhanced while at the same time accepting the needs for traffic
movement. Specialist advice as to the heritage value in economic terms may be helpful. Where
there are quite clear conflicts they need to be identified and resolved.
Unfortunately, in most areas in the country this careful consideration and evaluation of transport
and heritage objectives is only attempted in a few isolated prestige projects. Normally the two
strands are kept separate.

9.12.3 Local decisions made incrementally and in isolation
If only a few prestige projects attempt to consider both transport and heritage aspects, the
on–going work of maintenance and continual adjustment is very seldom carried out in the spirit
of original projects.
Understandably highway maintenance work is an on–going process. In urban areas there are
constant adjustments to the traffic arrangements. These may include:
❍
❍
❍
❍
❍
❍
❍
❍

pedestrianisation;
widening of footways;
alteration and designation of pedestrian crossings;
the addition of cycle ways to the existing carriageway;
the designation of bus lanes;
installation of new traffic signal schemes
installation and updating of street lighting, and
introduction of CCTV systems.

All this activity can take place within a single length of high street, yet each part would be
separately financed and programmed. In some cases they would be carried out by separate
agencies.
The resulting visual effect can be one of chaos. There is little or no visual co–ordination and
each element is more likely to adhere to national guidelines than to considerations of what is
most appropriate visually for the enhancement of the heritage of the area.
As a result all high streets have gradually come to look very similar. Local distinctiveness has
been lost and very little regard given to the heritage of the locality.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

231

9.13 Improving current practice
Without reducing the safe and efficient use of road space, there are techniques which cater for
the required traffic flows, and at the same time contribute positively to the enhancement of the
built heritage.

9.13.1 Materials
Historically local materials were used for paving. This automatically gave a local flavour to all
areas. Similarly local–building materials helped to clearly establish local or regional variations.
Even today historic buildings in some areas may be wholly in brick or stone or flint as these
were the most available local materials. As transportation became more economic, the use of
local materials was overtaken by nationally used building materials and techniques. The same
applied to paving materials. Granite was used in Cornwall and sandstone in Yorkshire. By the
18th century Purbeck limestone was being used in the City of London and with the advent of
the railways in the 19th Century the use of York Stone became widespread.
Where historic materials survive it is an objective of heritage conservation to keep them.
Sometimes more practical alternatives are needed, for instance in many historic places, street
surfaces were little more than rammed earth and rubble. Today bound macadam, with the
appropriate coloured aggregate surface dressing may be a natural successor. In all cases, the
design life of materials will be an important consideration. The scale of materials also needs to be
considered, for example, the size of the individual paving slabs or units is often important. Careful
reference to what was traditional in the location helps decide what would be appropriate.
Practitioners familiar with their own locality will probably instinctively select materials that are
visually appropriate, however it is seldom the case that practitioners have that advantage as staff
within organisations change frequently and individuals may not have local experience.
A procedure of noting the traditional details in a locality needs to be carried–out. This will
entail examining any remaining historic surfaces and noting the materials and local
workmanship techniques. Often these traditional materials are more likely to have survived in
less well–used or altered streets and in the courtyards and alleys off a main road.
An important requirement is that footway paving should be sufficiently robust to withstand
expected wear and possible vehicle loads. Until a few decades ago, local authority
specifications only had to indicate the material to be used and leave the details of construction
to the craftsman in the authority’s works department. They would have the skill and local
knowledge to carry out the work as specified and satisfactorily deal with the edges and
junctions of one material with another. Today this approach can lead to visually unacceptable
results. This is because the current system splits the client function from the contractor. It
requires accurate specification, designs and instructions as to workmanship, as well as close
supervision and insistence, by the client, that the contractor complies with all the requirements
of the specifications.

9.13.2 Signing and street furniture
In the past, many planned streets were characterised by a pervading sense of visual order. This
included the design and siting of all street furniture. Modern traffic and the diverse use of streets
now require a whole range of street furniture to respond to various practical needs. In order to
retain and enhance the basic visual co–ordination of a street, it is possible to reduce traffic
signage and street furniture clutter through a series of related measures.
The principles are to remove redundant signs and equipment, reduce unnecessary support posts
by putting as many signs on the same post or on adjacent walls. The aim is to combine as many
232

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

functions as possible. For instance bus shelters can incorporate payphones, seats, litterbins and
pedestrian direction signs. Equipment should be located as discretely as possible and be painted
in a single colour chosen to respect the location.
None of these practices in any way ignore the need for clear traffic regulation signs and signals
erected in accordance with the Traffic Signs Regulations and General Directions. Indeed if the
Regulations are studied carefully they reveal a number of discretionary powers in interpretation
available to local authorities. Unless it is part of a well considered design scheme, the
installation of over embellished street furniture does not enhance heritage. On the contrary it
detracts from the genuine quality of historic spaces and artefacts.

9.13.3 Access
Concern for the welfare of people with disabilities is understandably increasing. Tactile paving
is being used widely to assist people with sight difficulties to realise that, where the kerb has
been removed, they are leaving the safety of a footway and walking into a carriageway (IHT,
1991 and DETR, 2000 forthcoming). The official recommendations of red and contrasting
colours are relaxed in conservation areas. As a general rule it is important to obtain advice from
local disability groups relating to a particular location or project. People with visual
impairments use a whole range of non–visual indicators to find their way about an area with
which they are familiar and designers need to be aware of them.
The layout of tactile paving needs to be designed with more care than ordinary paving (DETR,
1999). This is because it frequently occurs at places where there are access covers or awkward
corners and problems that need to be resolved before work starts on site.
Generally, the fewer obstacles the better it is for people with disabilities. For this reason the
removal of street furniture, clutter and bollards greatly helps them as well as contributing
towards the overall enhancement of an area.
Those with visual impairments face difficulties in crossing large pedestrian areas safely.
Sensitive use of tactile paving can provide routes so that hazards are avoided (DETR, 2000
forthcoming).

9.13.4 Lighting
Lighting is a specialised subject, which allows the opportunity for subtleties far beyond the
normal practice. Street lighting is normally intended to give basic assistance to highway users
and provides a uniform level of illumination (Institution of Lighting Engineers, 1995, 1999).
There are opportunities to extend beyond this basic requirement. For example, the lanterns
themselves can be fixed to walls and thereby reduce the clutter of lamp columns.
Lighting can be mounted on buildings so that the lanterns fit in exactly with the architectural
details of the buildings. This will need the sizes and intensity of illumination of each lantern to be
accurately calculated. A variation in illumination is not necessarily unacceptable to the objectives
of traffic safety. There are also opportunities to think laterally and enhance the appearance of
historic structures through sympathetic lighting that also meets highways requirements. The City
of London, Glasgow and Edinburgh all use wall mounted lighting extensively.
In rural areas the introduction of new highway lighting, possibly for safety reasons, into
previously unlit areas can blur the distinction between urban and rural character, changing the
quality of the areas and creating the feel of urban sprawl, even where little additional building
spreads into the countryside. There needs to be major safety advantages before lighting is
provided in rural areas.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

233

9.13.5 Traffic calming
With the introduction
of traffic calming there
are opportunities to
combine traffic safety
objectives
with
conservation
and
heritage enhancement
(DETR, 2000). Once
traffic speeds have
been reduced, traffic
signs can be reduced
in size and frequency
because drivers have
more time to read
them. Similarly many
of the physical features
used to help drivers
keep to slower speeds
can
incorporate
features
that
are
already in the historic
landscape.

Some existing features in the street scene have a natural traffic
calming effect. Hampstead.

New traffic calming devices can be designed to continue the local architectural characteristics.
York.
234

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Some historic areas already
include townscape features,
which have a natural traffic
calming effect. For instance,
buildings may be set forward
into the road, there might be
tight radii, narrow carriageways
or cobbled streets as well as
traditional
gateways
and
pinch–points. Using the existing
layout of buildings and natural
features can be a very effective
means of speed control without
the need to introduce features
such as road humps and white
lining, onto the highway.
Entry treatments can echo the
local details. A study of local
Courtesy pedestrian crossings designed to reduce street
traditions or distinctiveness will
clutter and lines are constructed in simple natural
often include a range of local
materials used in the local materials. Shrewsbury.
manner and can be seen in
gateways, private entrances and access ways. If an area has a number of houses with large front
gardens and substantial white gateposts, this is a detail that could be incorporated into traffic
calming gates.
In urban areas the construction detail of adjacent boundary walls or railings can be used as a
base for new traffic calming. The conservation objective in each case is to achieve a
harmonious visual effect. Ideally the additional traffic calming measure should not look as
though it has been crudely added into the scene, it should appear as though it has always been
there or has at least been designed by the same hand as the original.
The intention should be, wherever possible, to adapt existing natural features to control driver
behaviour.

9.14 Examples of interdisciplinary considerations
9.14.1 Strand, London
In the award winning refurbishment of the Strand, London, all the street furniture was reviewed.
Modern lanterns fixed to large historic lamp columns provided most of the street lighting. The
columns were listed.
The scheme aimed to enhance the lamp columns, which were cleaned, repainted and guarded
and replaced in their traditional position at the centre of the road.
As much street furniture clutter as possible was removed. This included guard–rails, which at
one place had been erected on both sides of the road and at the centre reservation. Removing
the guard–rails required a decision at a high level in the authority as the argument for retaining
them for safety reasons had to be balanced against the argument for removing them for amenity
reasons. In the event since they have been removed, there have been no reported accidents that
could arguably have been prevented by the guard–rails. Removing the kerbside rails had an
additional amenity advantage. Once they were removed, the number of illegal kerbside
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

235

magazine dispensing boxes
and other boxes dumped at
the kerbside next to the
railings was considerably
reduced.
All of the centre road
pedestrian refuges with guard
rail waiting areas were
removed
and
became
unnecessary when the traffic
signal arrangements were
changed to allow pedestrians
to cross both carriageways at
a single crossing. Traffic in
both directions was stopped at
the same time.
In addition to removing all the
refuge
guard–rails,
the
number of signal heads, traffic
signs and their supports were
reduced. There is now a
considerable reduction in
street furniture clutter.

9.14.2 Hennef, Germany
The Strand scheme is very
similar to that introduced into
Hennef, Germany. An urban
regeneration
and
transportation improvement
scheme focussed on the needs
of pedestrians in the centre of
town. It was estimated that
60% of pedestrians crossed
the road at random. Rather
than channel them to formal
crossing points a central
reservation, one metre wide,
was provided to enable safe
crossing along the whole
length of the carriageway in
the
town
centre.
Signal–controlled crossings
were also provided and are
used by the infirm and
children in particular. The
design of the scheme used
engineering measures to avoid
the need for signing, white or
yellow lines and so on. For
example, traffic was slowed
by the narrowness of the
236

At Strand, London, pedestrian crossings have been simplified,
guard rails removed, clutter has been reduced, the setting of
the adjacent historic buildings has been enhanced and the
economic well–being of the area improved.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

carriageway combined with a continuous rumble strip. Parking was laid out in a “herringbone”
fashion so that cars leaving spaces slowed traffic further. Overall the comprehensive renewal
scheme reduced the need for intrusive street furniture, signs and highway lines. Slower speeds
and considerate parking became acceptable patterns of behaviour influenced by good highway
and urban design.
A similar approach has been adopted in Borehamwood, Hertfordshire.

9.15 Repairs
The New Roads and Streetworks Act 1991 requires statutory undertakers and their contractors
to be responsible for carrying out the permanent reinstatement of the highway where they
disturb it. Statutory undertakers are now required to reinstate the same materials as previously
existed, or the closest possible match.
For instance where there is a heritage interest, existing paving should be lifted, set aside
carefully, and reinstated to match adjacent areas as closely as possible to avoid ugly scars.
Existing historic street furniture of interest such as metal kerbs, pillar boxes, red telephone
boxes, drinking fountains, cattle troughs, monuments, plaques, memorials and lamp columns
should be preserved in situ, and wherever possible brought back into use. It may not be possible
for all features to be returned to their original use, however – cattle troughs, for example, can
be used as planters. Many authorities have compiled inventories of items of interest and
established clear lines of responsibility for future maintenance.

9.16 Where to find further information
The book referred to by many contemporary urban designers in this country is The Concise
Townscape (Cullen, 1961). Through photographs, sketches, diagrams and straightforward text,
Cullen points out the delights to be experienced in seemingly every day scenes. He shows how
many scenes have been eroded by thoughtless additions and demonstrates what can be done to
restore the original quality.
More recent publications build on these and similar basic texts. They remind readers to think of
how the principles of urban design can be applied to specific locations: Edinburgh Streetscape
Manual (City of Edinburgh/Davis) or City Streets (Corporation of London). Others deal with the
arduous but necessary detail of practical implication: Traffic Measures in Historic Towns
(English Historic Towns Forum/Davis).
Some deal with specialist subjects and show how technical considerations can be reconciled
with urban design principles: Lighting the Environment (Institute of Lighting Engineers).
Among the titles in the attached reference list are government policy statements such as
Planning Policy Guidance Note 15 (PPG 15) – P lanning and the Historic Environment
(Department of the Environment/Department of National Heritage). This and other PPGs
emphasise the importance that the government places on urban quality.
The basic law relating to highways and statutory instruments such as Traffic Signs Regulations
and General Directions (DETR) are required reading. These need to be considered with great
care as their requirements are mandatory. However, there are opportunities to interpret some
regulations. A collection of officially acceptable variations and amendments are described in
documents such as Historic Core Zone Projects (English Historic Towns Forum). The report
publishes the result of experiments at four historic town centres in conjunction with DETR to
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

237

examine the feasibility of adapting statutory requirements in order to conform more fully with
urban design concepts.

Places, Streets & Movement , a companion guide to the government’s Design Bulletin 32
Residential Roads and Footpaths (DETR/Alan Baxter & Associates) describes good practice that
can be achieved in the careful design and implementation. It is particularly appropriate for the
design of new residential areas.
Finally, there are publications from abroad about how other countries deal with similar issues.
These books often point the way to the future. The introduction of Homezones is a concept from
Europe, now being tested in this country. Improved Traffic Environment – A Catalogue of Ideas
(English Language by Road Directorate, Danish Ministry of Transport). Also bringing examples
from other European countries is Traffic in Townscape – Ideas from Europe (Civic Trust & English
Historic Towns Forum/Davis).

9.17 Principal recommendations
1. Manage individual or groups of building holistically along with the associated highways.
2. Use all available opportunities to improve the highway environment.
3. Attention to detail is vital.
4. Use local materials for construction and maintenance.
5. Remove unnecessary street furniture or relocate it if necessary.
6. Do not let road–side infrastructure dominate the highway environment
7. Co–ordinate street design and maintenance with appropriate agencies.
8. Use natural features to influence road–user behaviour such as in traffic calming schemes.

References

238

Cullen G, 1961

The Concise Townscape. Architectural Press, London.

DETR, 1999

Guidance of the Use of Tactile Paving Surfaces. DETR,
London.

DETR, 2000 (forthcoming)

Mobility for All. DETR, London.

The Institution of Highways &
Transportation, 1991

Reducing Mobility Handicaps: Towards a Barrier Free
Environment. IHT, London.

The Institution of Highways &
Transportation, 1997

Transport in the Urban Environment. IHT, London.

Institution of Lighting
Engineers, 1995

Lighting the environment: A guide to good urban lighting:
Institution of Lighting Engineers August 1995.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Institution of Lighting
Engineers, 1999

A Practical Guide to the Development of a Public Lighting
Policy for Local Authorities , Technical Report No 24. ILE,
Rugby.

Further reading
Additional sources of information on good practice for the public realm are included in the
following list compiled by English Heritage.

Bloomsbury Street Audit Study : Davis, Colin J for English Heritage/London Borough of Camden
June 1994.
Brixton Streetscape Manual : Davis, Colin J for Brixton City Challenge/English Heritage/London
Borough of Lambeth October 1996.
City/people/light : Philips 1997.
City Streets – improving the city street scene: A Guidance Note: Corporation of London July
1996.
Cluttered Countryside, The : CPRE December 1996.
Conservation and Contradictions : CCTV Today May 1997.
Decorative Lighting of Churches : Electrical Contractors Associates: 1996.
Details in the Street Scene : A Conservation Policy: Royal Borough of Kensington & Chelsea
1993.
Edinburgh: Streetscape Manual : Davis, Colin J for the Scottish Office/Lothian Regional
Council/Edinburgh City Council/Historic Scotland/ENTCC/EOTRT November 1995.
Greenwich Town Centre Streetscape Manual : London Borough of Greenwich January 1999.
Historic Core Zone Projects, The : English Historic Towns Forum November 1999.
Improved Traffic Environment – A Catalogue of Ideas (in English) : Road Directorate, Danish
Ministry of Transport 1993.
Improving Design in the High Street : Royal Fine Art Commission 1997.
Landscape Detailing (3rd Ed): Michael Littlewood 1994.
Landscape Design Guide (2 Volumes): Adrian Lisney 1990.
Landscape Strategy for London’s Trunk Road Network : Highways Agency November 1995.
Lighting Equipment as Daytime Architecture : Peter Heath, Lightec ‘96 Conference papers 1996.
London Bus Priority Network – Sector Proposals: London Bus Priority Network/London Transport
Buses/London Boroughs 1999.
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

239

London’s Urban Environment: Planning for Quality : Building Design Partnership for
Government Office for London 1996.
Managing Urban Space in Town Centres: A Good Practice Guide : DoE/Association of Town
Centre Managers 1997.
Network Plan for Red Routes : Traffic Director for London March 1993.
Places, Streets & Movement : A companion guide to Design Bulletin 32 Residential roads and
footpaths: Alan Baxter & Associates for DETR 1998.
Planning and the Historic Environment : Planning Policy Guidance Note 15 (PPG15):
Department of the Environment/Department of National Heritage September 1994.
Protecting the Street Scene : Context Issue No. 41 1994.
Residential Roads and Footpaths : Design Bulletin 32, Department of Transport 1992.
Revision to the Network Plan Traffic Director for London October 1998.

Seven Dials Renaissance: The Environmental Handbook : Civic Design Partnership for the Seven
Dials Monument Charity September 1999.
Street Design Guide : London Borough of Richmond upon Thames July 1995.
Streets Design in Merton : London Borough of Merton 1999.
Street Improvements in Historic Areas : English Heritage August 1993.
Street Furniture Manual : Westminster City Council 1993.
Streets as Living Space : Carmen Haas–Klau, Graham Crampton, Clare Dowland, Inge Nold 1999.
Supplement to the Network Plan : Traffic Director for London March 1995.
Tomorrow’s Towns : Institution of Civil Engineers, 1994.
Towards an Urban Renaissance : Urban Task Force 1999.
Traditional Paving and Street Surfaces : Fact File No 3, National Council of Civic Trust Societies
1996.
Traditional Paving Design : Proceedings of a Workshop Seminar: University of the West of
England/Somerset County Council 1994
Traffic Calming Bibliography, DETR Traffic Advisory Leaflet, TAL 5/00, 2000.

Traffic in Historic Town Centres : English Historic Towns Forum 1994.
Traffic in Townscape: Ideas from Europe : Davis, Colin J for English Historic Towns Forum 1994.
Traffic Management and Parking Guidance : DETR 1998.

240

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Traffic Management in Historic Areas : Traffic Advisory Leaflet 1/96: Department of
Transport/English Heritage 1996.
Traffic measures in Historic Towns : An introduction to good practice: Davis, Colin J for Civic
Trust/English Historic Towns Forum 1993.
World Squares for all Masterplan Foster & Partners et al 1998.

Specific Government legislation and guidance on roads and footways is covered by:
Highways Acts 1980–99.
Road Traffic Act 1991.
New Roads and Streetworks Act 1991.
Road Hump Regulations Statutory Instrument 1996/1483.
Traffic Advisory Leaflets 1991–2000.
Traffic Calming Act 1992.
Traffic Calming Regulations Statutory Instrument 1993/1849.
Traffic Signs Regulations and General Directions: Statutory Instruments 1994–99.
Traffic Director for London’s technical guidance documents 1993–9.
British Standards Institute:
Specification for dressed natural stone kerbs, channels, quadrants and setts BS435 1975/1993.
Precast concrete flags, kerbs, channels, edgings and quadrants BS7263 Pts 1&2 1994/1990.
Guidance for trees in relation to construction BS5837 1991.
Recommendations for transplanting rootballed trees BS4043 1989.

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

241

242

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

I NDEX
Subject
A
A–weighting, and human hearing
abatement techniques
access, built heritage
accessibility, as NATA criterion

Section
6.2.4
2.3.3
9.13.3
Table 2.1,
Table 2.2

accidents
source of pollutants
4.4.3
see also safety
ACEA, and European Auto-Oil Programme
2.3.3
acid deposition
5.1, 5.2.2
Advisory Committee on Trunk Road Assessment
(ACTRA)
2.2.1
report
5.2.1, Box 5.2
aftertreatment systems, and vehicle
emission reduction measures
5.8.1
aggregates provision
2.4.3
air pollution
effect on verges
8.5.3, Figure 8.2
and environmental and social costs of
road transport
Table 2.10
modelling
5.6.2, Box 5.17
monitoring, and NAQS
5.6.1, Box 5.14,
Box 5.15, Box 5.16
air quality
1996 concentrations
Box 5.7
and 1998 White Paper daughter document 2.4.2
current situation
5.2.2
and European Auto–Oil Programme
2.3.3
highways maintenance
3.5
impact assessment, current practices
5.3
international agreements
5.5.3
issues
5.4
local management
5.5.4
as NATA criterion
Table 2.1, Table 2.2
and noise
6.6.4, 6.7
overview
5.2.1
parties affected
Box 5.2
pollution control and reduction
5.7
see also pollution, control and reduction
and pollution from vehicles
4.4.1
practical measures to reduce pollution
5.8
RCEP report
2.2.1
recommendations
5.9
review and assessment of air pollution
5.6
standards
5.5.2
statistics
Table 2.8
and Transport 2010
2.4.4
and trees
7.3.3
and tunnels
6.6.5
and UK transport policy
2.4.3
vehicle and fuel standards
5.5.1, Box 5.5
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

air quality management
5.1–5.9
airports, and 1998 White Paper
2.4.1
alternative fuels
5.8.1
aluminium, as pollutant
4.3.2
ancient monuments
9.2, Box 9.6
Ancient Monuments and Archaeological
Areas Act 1979
Box 9.6
annual average daily traffic (AADT),
and water management
4.2, 4.7.2, Table 4.1
Appraisal Summary Tables (ASTs), and
trunk road schemes
2.4.2
archaeology, built heritage
Box 9.6
Areas of Outstanding Natural Beauty,
and environmental impact assessments
3.2
Areas of Special Protection (AOSPs), and birds 2.5
arsenic, and air quality
5.5.2
asphalt, porous, as alternative road surface 4.6.5.2
atmospheric deposition
4.4.4
atmospheric dispersion
5.4.2
atomic absorption spectrophotometry, and lead
5.6.1
audits, and EMS
3.8, 3.9.2

B
bacteria, as pollutants
4.3.4
badgers, and nature conservation
8.6.3
balancing ponds, and highway runoff
4.6.4.4
barriers, and noise
6.7
basins, and highway runoff
4.6.4
benchmarking, and road traffic reduction
2.5
benefit cost ratios (BCR), and trunk road schemes
2.4.2
benzene see hydrocarbons
best value, and EMS
3.3
biodiversity
8.1–8.10
and trunk road schemes
2.4.2
see also nature conservation
birds
8.4.5, 8.6.3, 8.7.2
boreholes, and trunk road schemes
2.4.2
bridges, and rural landscapes
7.3.5
British Standards
BS 5228, and noise, Noise and vibration
control on construction and open sites
6.5.2
BS 5837, trees, and urban landscapes,
Guide for trees in relation to construction 7.3.3
BS 6367, and gully pots,
Code of practice for
drainage of roofs and paved areas
4.4.6
BS 7750, as standard, Specification for
environmental management systems
3.6.1
BS 8233
and noise
6.6.6
Sound insulation and noise reduction for
buildings
6.5.5
and fuel
5.5.1
British Transport Police
2.4.1
brownfield sites, and Local
243

Subject

Section

Development Plans
6.6.1
Brundtland, Gro Harlem, report’s definition of
sustainability
3.1
Buckinghamshire, roadside nature conservation
moth case study
8.8.1, Figure 8.4
buildings
as built heritage
9.3
and noise
6.6.6
as noise barriers
6.6.3
built heritage
ancient monuments
9.2
challenges to enhancement of
9.12.1–9.12.3
conservation and Conservation Areas
9.4
cultural heritage
9.8.1
economic well–being
9.8.2
everyday life
9.10, Box 9.2, Box 9.3, Box 9.4
groups of buildings
9.3
and highway management
9.11
highways maintenance
3.5
identity and clarity of location
Box 9.2
improving current practice
9.13
interdisciplinary considerations
9.14
as landscape
9.9
legislation and official advice
Box 9.6
listed buildings
9.2
and management of highways
9.1–9.17
recommendations
9.17
regeneration
9.8.3
repairs
9.15
sense of place
Box 9.1
spaces
9.5, 9.6
street clutter
Box 9.5
and streetscape
9.7
bus lanes
5.8.1, 5.9
bus policy
2.4.2
bus services
2.2, 2.4.1, 2.4.4, 2.4.1
buses, and vehicle emission reduction
measures
5.8.1, Box 5.9, Box 5.24
1,3–butadiene see hydrocarbons
bypasses, and vehicle emissions
5.8.2

C
cadmium
4.3.2, 5.5.2
calcium magnesium acetate
4.3.4
“Calculation of Road Traffic Noise” (CRTN) 6.3.1,
6.5.7, 6.5.6, 6.5.4, 6.6.3, 6.6.2
Cambridge Water Company, litigation
4.5.1
carbon dioxide emissions
5.1, 5.2.2, Box 5.8
and air quality
5.1
and DMRB
5.3
and increase in road transport
5.2.2, Box 5.8
Kyoto Conference
2.3.1
RECP report
2.2.1
reduction measures
Box 5.23
and trunk road schemes
2.4.2
244

and UN Framework Convention on
Climate Change
5.5.3
carbon monoxide
and air quality
5.1, 5.2.2, 5.2.1
and Air Quality Framework Directive
5.5.2
and cold vehicles
5.4.1
concentration level
5.4.2, Box 5.12
current situation
Box 5.7
and DMRB
5.3, 5.6.2, 5.7.2
effect on verges
8.5.3
and European Auto–Oil Programme
2.3.3
and hydrocarbons
5.6.1
and NAQS
5.6.2, Box 5.6
and speed
5.8.1
and vehicle emissions
5.4.1, Box 5.9
and vehicle and fuel standards
5.5.1
cars
unit external costs
Table 2.9
see also motorists
catalysts
and cold vehicles
5.4.1
EU Directives regarding 5.2.1, Box 5.4, Box 5.5
and NOX
5.4.1
and vehicle emissions
5.4.1, 5.8.1, Box 5.9
chemicals
and GQA classification
4.5.2, Figure 4.2
and verges
8.5.2, 8.7.3, 8.10
chemiluminescence analysis
5.6.1
chlorides, as pollutant
4.3.4
chromium, as pollutant
4.3.2
“city” fuels, and vehicle emissions
5.8.1
City of Westminster, Strand, street furniture 9.14.1
clean vehicles, development
5.9
climate, and DMRB
5.3
climate change
2.4.2, 2.6.2, Table 2.10
coach services
2.2
coastal protection schemes
3.2
coastal shipping, and 1998
White Paper
2.4.1, 2.4.2
cold vehicles, calculations
5.6.2
colour, and built heritage
Box 9.4
Commission for Architecture and the
Built Environment
9.1
Commission for Integrated Transport
(CfIT)
2.4.1, 2.5
communication, as ecological issue
8.5.6
communities, response to noise
6.4.5
community organisations, and 1998
White Paper
2.4.1
community severance, as NATA
criterion
Table 2.1, Table 2.2
compensation claims, and noise
6.5.3, 6.7
compliance improvement, and highways
environmental management model 3.9.1, Figure 3.5
compliance improvement process
Figure 3.5
Compulsory Competitive Tendering, and
landscape management
7.4.4
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Subject

Section

congestion
and 1998 White Paper
2.4.1
costs
Table 2.10
road pricing
2.2.1
and Transport 2010
2.4.4
and vehicle emissions
Box 5.23
conservation, and built heritage
9.4
Conservation Areas
2.2.1, 7.3.3, 9.4
constructed wetlands, and highway
runoff
4.6.4.5, Box 4.6
consultation, public, and trunk road schemes 2.4.2
contractors
and materials
9.13.1
and nature conservation
8.5.5, 8.10
Control of Major Accident Hazards
Regulations 1999 (COMAH)
3.2, 3.9.3
Control of Pollution Act 1974, and water
management
4.5.1
copper, as pollutant
4.3.2
cordon charges, as vehicle emission
reduction measure
5.8.1, Box 5.23
cost, implications of EMS
3.3
cost benefit analysis (COBA)
and noise
6.7
and road appraisal
2.2.1
costings, and water management
4.7.1, Table 4.4
countryside, and 1998 White Paper
2.4.1, 2.4.2
Countryside Agency
map, landscape
7.4.1
publications
landscape
7.4.8, 7.4.1
landscapes
7.3.5
lighting
7.3.2
and rural landscapes
7.3.5
Countryside Commission, and trunk road
schemes
2.4.2
county wildlife trusts, and nature
conservation
8.6.6, 8.10
cultural heritage, and DMRB
5.3
culture, and built heritage
9.8.1
customer care, public transport
2.4.1
cuttings, and noise
6.6.5
cycle lanes
5.8.1, 5.9
cycling
and 1998 White Paper
2.4.1
PPG 13
2.4.3

D
dangerous substances, EU directive
Dartmoor National Park
daughter documents, 1998 White Paper
decibels see noise
Design, Build, Finance and Operate (DBFO)
schemes
2.2,
Design Manual for Roads and Bridges (DMRB)
and air pollution modelling
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

4.5.3
7.6.2
2.4.2
7.4.3
5.6.2

air pollution modelling
Box 5.18
Environmental Function and Landscape
Element
7.5
landscape design
7.4.2
landscape improvements
7.3.2, 7.3.1
and MEA
5.3
noise annoyance
6.4.2
noise barriers and landscaping
6.6.3
noise management issues
6.5.7
non–porous quiet road surfaces
6.6.2
PPG 24
6.5.2
superceded by NAQS
5.6
use in calculations
5.7.2, Box 5.21, 6.3.1
detrunking
7.5, 8.5.6
developing countries, and EMAS potential as trade
barrier
3.6.1
Devon, and rural roads case study
7.6.2
diesel vehicles
5.2.1, 5.4.1, 5.5.1, Box 5.9
diffraction, and noise
6.6.3, 6.6.5
diffusion, and monitoring NOX
5.6.1
directives see European Union
disabled people
access, built heritage
9.13.3
PPG 13
2.4.3
distribution, freight policy
2.4.2
disturbance, of land
8.5.4, 8.10
drainage, and water
4.1–4.7
Drinking Water Directive
4.4.5
“dust and dirt (DD)” see particulates

E
earth bunds, and noise
6.6.3, 6.7
Eco–Managment and Audit Scheme
Regulation (EMAS), as standard
3.6.1, Table 3.2
ecological inventories, and landscape
management
7.4.9
ecology
8.1–8.10
see also nature conservation
economic instruments, and traffic
management
2.2.1
economy and built heritage
9.8.2
as NATA criterion
Table 2.1, Table 2.2
and trunk road schemes
2.4.2
education, integrated transport policy
2.4.1
Education, Department for, Design Notes
6.5.5
elderly, bus concessions for
2.4.1
electronic road pricing
2.4.2
emergencies, and groundwater
4.5.5
emission control
recommendations
5.2.2
standards
5.4.1, Box 5.5, 5.8.1
EN 1793, noise barriers
6.6.3
enclosures, and noise
6.6.5
energy efficiency, highways maintenance
3.5
enforcement, role of UKEA
3.2
engineering
245

Subject

Section

and noise
6.5.2
and water
4.7.1
engines
technology
2.3.3
vehicle emissions
5.4.1
England, regions, and 1998 White Paper
2.4.1
English Heritage
2.4.2, 9.1, 9.8.3
English Nature
2.4.2, 8.4.3, 8.6.4
map
7.4.1
Environment Act 1995
2.5, 3.2, 5.2.2, 5.5.4
Environment Agency (UKEA)
2.4.2, 3.2, 3.4,
3.9.1, 4.5.6, 4.5.1
environmental appraisal
2.6.2
environmental aspects in product standards
(EAPS)
3.7.2
environmental assessment
4.5.3, 6.5.2, 7.3.1
Environmental Assessment Directive
4.5.3
environmental auditing
3.7.1
environmental costs
Table 2.10
environmental impact assessments
3.2, 4.5.3,
Box 4.3
environmental impacts
2.2.1, 2.3.2, Table 2.1,
Table 2.2, 3.4, Figure 3.1, Figure 3.2, Figure 3.3
environmental issues
3.8
environmental labelling (EL)
3.7.2
environmental management procedure
Box 3.3
environmental management systems (EMS) 3.1–3.10
creation
3.8
delivery
3.5
framework
3.6
future trends
3.10
highways environmental management model 3.9
key consideratiosn
3.4
legislation and regulation
3.2
organisational considerations
3.3
protection
3.1
sample Manual contents
Box 3.3
standards
3.6.1, 3.7.1, 3.7, Box 3.3
environmental performance
evaluation (EPE)
3.7.1
Environmental Protection Act 1990
3.2, 8.6.1
environmental protection and management
3.1
environmental risks
3.9.1.–9.12, Figure 3.3
Environmental Statements
7.4.2
erosion
4.4.2, 8.5.4, 8.10
Essex, roadside nature conservation special
verges case study
8.8.3
Europea, noise barriers and landscaping
6.6.3
European Auto–Oil Programme
2.3.3, 5.5.1
European Commission
2.3.2, 2.3.3
see also European Union
European Community
2.3.2, 2.5, 2.6.1
see also European Union
European Court of Justice
2.3.2
European Environment Agency, as regulatory
authority
3.4
246

European Programme on Emissions, Fuel
and Engine Technology
2.3.3
European transport policy
2.3.2
European Union
air quality
5.2.1, 5.5.1
Air Quality Framework Directive
5.5.2
directives
3.2, 3.4
Drinking Water Directive
4.4.5
Eco–Managment and Audit Scheme
Regulation (EMAS)
3.6.1
Environmental Assessment Directive
5.3
Freshwater Fisheries Directive
2.4.2
Groundwater Directive
4.3.3
landscape
7.3.1
MEET project
5.6.2
noise
6.4.2, 6.5.2
SSSIs
8.6.1
water management
4.5.3
Europia, and European Auto–Oil Programme 2.3.3
Event Mean Concentrations (EMC), and
water management
4.2, Table 4.1
Expert Panel on Air Quality
5.1
Exposed Aggregate Concrete (EAC)
6.6.2,
Figure 6.2
extended detention basins, and 4.6.4.3, Table 4.3,
highway runoff
Table 4.5, Table 5.2
external spaces, and built heritage
9.11.1

F
façade noise levels
6.2.9, 6.4.2
fad chasing, and EMS
3.3
fauna see wildlife
fertilisers, as pollutants
4.3.4
filter drains, and highway
4.6.2,
runoff
Table 4.3, Table 4.4
filter strips, and highway runoff
4.6.1, 4.6.1.1,
Table 4.5
Fire Service, spillages, and groundwater
4.5.5
fisheries, legislation
4.5.1
fisheries, freshwater
2.4.2
flame photometry
5.6.1
flood defence
2.4.2, Table 2.6, 4.5.1
flora see plants
footways, materials
9.13.1
forecasting, variable nature
2.2.1
Forestry Authority
8.6.1
Framework Dangerous Substances Directive 4.5.3
free–field noise levels
6.2.9, 6.4.2
freight, and air quality
5.9
freight grants
2.4.1
freight policy
2.4.2
freight transport
2.2.1, 2.3.2, 2.4.1, 5.2.2,
5.4.1, 6.3.1
and vehicle emissions
5.4.1, 5.8.1, Box 5.9,
Box 5.23
freight vehicles, and
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Subject
vehicle emissions
freshwater fisheries
fuel
consumption
efficiency
emissions
fuel duty
Fuel Price Escalator
fuels, alternative

Section
5.8.1, Box 5.24, 5.8.1
2.4.2, 4.5.3
5.4.1
2.4.1
5.4.1
5.8.1, Box 5.23
2.3.1
5.8.1

G
gas chromatography
5.6.1
Gaussian Plume, and NAQS calculation
5.6.2
General Quality Assessment (GQA) 4.5.2, Figure 4.2
General Quality Assessment (GQA)
grade (Chemical)
2.4.2
Geographical Information System (GIS) 7.5, 8.5.6,
8.7.6
geotextiles, and landscape design
7.4.2
Germany, Hennef, built heritage
9.14.2
global emissions, and trunk road schemes
2.4.2
global policy
2.3.1
glycols, as pollutants
4.4.5
grass, swales, and highway runoff
4.6.1.1,
Table 4.3, Table 4.4, Table 4.5
grasscrete, as alternative road surface
4.6.5.1
grassland, cutting
8.5.1, 8.7.2
green transport plans
2.4.1, 2.4.2
greenhouse effect
5.2.2
greenhouse gases see carbon dioxide
grit chambers, and highway runoff
Table 4.3,
Table 4.4, Table 4.5
groundwater
drainage and runoff management
4.1–4.7
regulations
4.5.4, Box 4.2
Source Protection Zones (SPZs)
4.7.3
and trunk road schemes 2
.4.2
Groundwater Directive
4.3.3
Groundwater Regulations 1998
4.5.4
Groundwater Resource Protection (GRP) zones
4.6.3.1
Guidance On Methodology for
Multi–modal Studies
(GOMMS), and trunk road schemes
2.4.2
gully pots
4.4.6, 4.7.3
gully systems
Table 4.3, Table 4.4, Table 4.5

H
hard landscaping
7.4.8
health
2.4.1, 5.2.1, Box 5.2
health, general, and noise
6.4.4
health and safety
3.8, 3.9.3, 3.9, 4.5.5
hearing, human, frequency selectivity
6.2.4
Hedgerow Regulations 1997
8.6.1
hedges, recommendations
8.10
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Helsinki Protocol, and air quality
5.5.3
herbicides
and Framework Dangerous Substances
Directive
4.5.3
and groundwater
4.5.4
limitations
4.7.3
as pollutants
4.3.4, 4.4.5
and soakaways
4.6.3.1
and verges
8.3, 8.5.7, 8.5.2, 8.7.3
heritage
2.4.2, Table 2.1,
Table 2.2, Table 2.5
see also built heritage
Hertfordshire, suburban roads case study
7.6.3
hexacyanoferrate, as pollutant
4.3.4
HGV lanes
2.4.4
HGVs
5.2.1, 5.5.1, 6.6.4, 6.7, Table 6.4
highway discharge acceptability matrix
4.7.2, Figure 4.3
highway environment, improvement
9.17
highway maintenance
8.4.4, 8.6
highway management
and built heritage
9.11
see also built heritage, and highway
management
and nature conservation 8.3, 8.4.1–8.4.7
see also nature conservation, and highway
management
highway runoff
4.6.1–4.6.5, Table 4.3,
Table 4.4, Table 4.5
highways
and built heritage
9.7
maintenance
3.5
Highways Act 1980 2.5, 4.5.6, 4.5.1, 6.5.2, 7.6.3
Highways Agency
and developments in landscape management 7.5
and landscape management
7.4.4, 7.4.3
and lighting case study
7.6.4
responsibilities
4.5.6
and transport policy
2.2
and urban roads case study
7.6.1
Highways Agency Road User’s Charter
2.4.1
Highways Agency Targeted Programme
2.4.4
Highways (Assessment of Environmental Effects)
Regulations 1988
4.5.3
Highways (Assessment of Environmental Effects)
Regulations 1999
3.2
highways authorities
4.5.6, 4.7.2, 8.7.5, 8.10
Highways Authorities Product Approval Scheme
(HAPAS)
6.6.2
highways environmental model
3.9, Figure 3.4
Highways (Traffic Calming) Regulations
1993
Box 9.6
Historic Core Zones
7.3.3
history, and townscape
9.6
hospitals
2.4.1, 6.5.5, 6.6.6
hot vehicles, calculations
5.6.2
housing, and UK transport policy
2.4.3
247

Subject

Section

human resources, and EMS
3.3, 3.8, 3.9.2
humans, response to noise
6.4, 6.4.1–6.4.5
Hybrid UTHMAL–VTSL
6.6.2, Figure 6.2
hydrocarbons
and air pollution monitoring
5.6.1
and air quality
5.1, 5.2.1, 5.2.2, 5.5.2
and calculation methods
5.6.2, 5.7.2
clearance and maintenance practices
4.4.6
and cold vehicles
5.4.1
current situation
Box 5.7
and DMRB
5.3
and European Auto–Oil Programme
2.3.3
and Framework Dangerous Substances
Directive
4.5.3
and infiltration basins
4.6.3.3
and infiltration systems
4.6.3
and NAQS
Box 5.6
as pollutants
4.3.3, 4.4.1, 4.4.2, 4.4.1
and porous pavement
4.6.5.1
and soakaways
4.6.3.1
and vehicle and fuel standards
5.5.1
and verges
8.5.3
hydrological cycle, and highways
4.1

3.4, 3.7, 3.8, Figure 3.6, Table 3.3
and ecological issues
8.5.6
environmental risks
3.9.1
landscape management
7.4.3
organisational evaluation
3.7.1
product evaluation
3.7.2
ISO 9000 series
3.10
and safety
3.10
international treaties, and UK legislation
3.2
investment, and Transport 2010
2.4.4
iron, as pollutant metal
4.3.2
ISO see international standards

J
Jefferson, J, and air quality
journey times, as NATA criterion

5.2.1
Table 2.1,
Table 2.2

K
Kent, roadside nature reserves and
wardens case study
Kyoto Conference, as influence on
domestic transport policy
Kyoto Protocol, and air quality

8.8.2
2.3.1
5.5.3

I

L

ice, and inorganic salts
4.3.4
impact assessment, air quality
5.3
incentive schemes, and vehicle emission reduction
5.8.1
inductively coupled plasma mass
spectrophotometry
5.6.1
infiltration basins
4.6.3.3
infiltration systems
4.6.3, 4.7.3, Figure 4.3
infiltration trenches
4.6.3.2, Table 4.3,
Table 4.4, Table 4.5
information system, public transport
2.4.1
infra red radiation
5.6.1
inland waterways, freight policy
2.4.2
inorganic salts, as pollutants
4.3.4
Institute of Environmental Assessment,
publication
7.4.1
Institution of Lighting Engineers,
and landscape improvements
7.3.2
Integrated Pollution Prevention and
Control Directive
2.3.2
integrated transport, and Transport 2010
2.4.4
integration
as NATA criterion
Table 2.1, Table 2.2
and transport policy
2.6.1
and trunk road schemes
2.4.2
international standards
ISO 14000 series, as standard
3.6.1, 3.7,
Table 3.3
ISO 14001 (Environmental Management
Systems – Specification with Guidance for Use)

lagoons, and highway runoff
4.6.4.2, Table 4.3
Land Compensation Act 1973, and noise
6.5.3,
6.5.4, 6.6.3
land constraints, and water management
4.7.1
land drainage, and trunk road schemes
2.4.2,
Table 2.6
land use planning
6.6.1
and air quality
5.8.1, 5.9, Box 5.23
integration with transport planning
2.2.1, 2.4.1
landowners, and nature conservation
8.6.7
landscape
and DMRB
5.3
as NATA criterion
Table 2.1, Table 2.2
and road network
3.1
and trunk road schemes
2.4.2
landscape design
7.4.2
Landscape Element
7.4.3, 7.5
Landscape Function
7.4.3
Landscape Institute
7.4.1
landscape inventories
7.4.9, 7.5
landscape management
7.1–7.7
case studies
7.6.1–7.6.4
future developments
7.5
guidance on best practice
7.4.1–7.4.10
introduction
7.1
issues
7.3
overview
7.2
recommendations
7.7
rural roads case study
7.6.2
suburban roads case study
7.6.3

248

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Subject

Section

urban roads case study
7.6.1
landscape management plans
7.4.5
Landscape Objectives
7.4.3
landscape professionals, optimum use of
7.7.1
landscaping
6.6.3, 8.4.7
lead
and air quality
5.2.1, 5.2.2, 5.5.2, 5.6.1,
Box 5.3, Box 5.6, Box 5.7
effect on verges
8.5.3
as pollutant
4.3.2, 4.4.1
legal liability, and water management
4.5.1
legislation
2.5
environmental impacts
3.4, Figure 3.2
environmental management systems
3.2
highways environmental management model,
environmental risks
Box 3.5
non–exhaustive list
Box 3.5
and water management
4.5
see also individual Acts; European Union
Leitch, Sir George, and air quality
5.2.1
Letchworth Garden City Heritage Foundation 7.6.3
life cycle assessment (LCA), ISO 14000
3.7.2
light pollution
3.9
light rail projects
2.4.4
light vehicles
5.5.1, 5.6.2
lighting
and built heritage
9.13.4
case study
7.6.4
and landscapes
7.3.2, 7.3.5
listed buildings
3.1, 9.2, Box 9.6
litter, and landscape management
7.4.5
Local Agenda 21
2.3.1, 3.3
local authorities
and 1998 White Paper
2.4.1
and 1998 White Paper daughter document 2.4.2
air quality
2.4.3
and air quality
5.5.4, 5.6
biological databases
8.6.6
case studies
8.8.1–8.8.3, Figure 8.4, Figure 8.5
and detrunking
8.5.6
environmental databases
7.5
and environmental impact assessments
Box 4.3
and environmental risks
3.9.2
and highway management
8.4.3
and highways management
9.12.3
highways powers
4.5.6, Box 4.4
and landscape management
7.2, 7.4.4, 7.5
and lighting
7.3.2
and Local Agenda 21
3.3
and nature conservation
8.6.1–8.6.2
and noise
6.5.1, 6.6.1
responsibility for built heritage
Box 9.6
and road traffic reduction
2.5
and roadside management
8.6.5
and street furniture and signing
9.13.2
and traffic management
5.7.1
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

and trees
7.3.3
and vehicle emissions
5.8.1, Box 5.23
and verges
8.5.1, 8.7.1, 8.7.2, Figure 8.3
and water management
4.5.1, Box 4.2
local character
and highways design
9.11.3
landscape management
7.7.1
Local Government Act 1992, and water
management
4.5.3
Local Nature Reserves, and roadside areas
8.6.1
Local Transport Plans (LTPs) 2.4.1, 2.4.2, Table 2.7
location, identity and clarity of, built heritage
Box 9.2
London
boroughs, road charging powers
2.4.2
and built heritage
Box 9.2, Box 9.3
and European Auto–Oil Programme
2.3.3
Richmond/Hounslow, urban roads case study
7.6.1
Strand, interdisciplinary project
9.14.1
and Transport 2010
2.4.4
and vehicle emission reduction measures 5.8.1,
Box 5.24
London, Mayor of
2.4.4, 2.4.1, 2.4.2
lorry bans
5.8.1, 6.6.4
low emission zones, proposals
5.4.1

M
M4 Bus Lane, proposal
2.6.1
Maastricht Treaty, and European transport policy
2.3.2
McAdam, John, and highway development
8.3
maintenance
and highway runoff
4.6.1–4.6.5, Table 4.4
importance
4.7.3
and landscape management
7.4.4
and sources of pollutants
4.4.1–4.4.6
and Transport 2010
2.4.4
management
and environmental risks
3.9.2
need for commitment to EMS
3.8
management contracts, landscape management
7.4.4
management plans
and landscape management
7.4.3
publications available
7.4.1
manganese, as pollutant
4.3.2
Manual of Environmental Assessment
(MEA)
2.2.1, 5.2.1, 5.3
material assets, and DMRB
5.3
materials
and built environment
9.17
used for surfaces
9.13.1
Mawhinney, Brian, and New Realism
2.2.1
MEET project, method used
5.6.2
mercury, and Air Quality Framework Directive 5.5.2
249

Subject

Section

metals
and highway runoff

4.6.4.4, 4.6.3.3,
4.6.3.1, 4.6.3
as pollutants
4.3.2, 4.4.6
and road surface
4.4.2, 4.6.5.2
and vehicles
4.4.1
methyl tertiary butyl ether (MTBE) see hydrocarbons
microorganisms, as pollutants
4.3.4
microphones, relative to reflective surfaces
6.2.9
Milk Marketing Board, and highway
development
8.3
Mineral Planning Guidance Notes (MPGs)
2.4.3
minor roads, intersections with major roads 7.3.5
modal shift, encouragement
2.2.1
modification, of EMS
3.8
monitoring, and EMS
3.8
MOT test, and vehicle and fuel standards
5.5.1
moths, roadside nature conservation case study
8.8.1, Figure 8.4
motor industry, and European Auto–Oil
Programme
2.3.3
motorists, and 1998 White Paper
2.4.1
motorways
and 1998 White Paper
2.4.1
and environmental impact assessments
3.2
and Transport 2010
2.4.4
and vehicle emission reduction measures 5.8.1,
Box 5.23
verges
8.2
vistas
9.7
mowers, and cutting regimes
8.7.2
MTBE (methyl tertiary butyl ether) see hydrocarbons
Multi–Layer Surface Dressings (MLSD)
6.6.2
Mummery, Joan, and Essex verges project
8.8.3

N
National Air Quality Strategy (NAQS)
2.4.3,
Table 2.8, 5.2.2, 5.3, 5.5.2, 5.6,
Box 5.6, Box 5.7
National Freight Corporation, privatisation
2.2
National Land Use Database
7.5
national parks
3.2
National Parks and Access to the Countryside
Act 1949
8.6.1
National Rivers Authority (NRA)
4.5.6, 4.5.1,
4.5.4, Box 4.2
National Water Council (NWC)
4.5.2, 4.5.6
natural heritage, highways maintenance
3.5
Nature Conservancy Council
8.8.3
nature conservation
assessment of options
Table 2.4
assessment of roadside areas
8.7.1
communication
8.5.6
conflicting needs of different species
8.4.5
costs
8.4.4
250

economic and practical considerations
8.5.5
erosion and disturbance
8.5.4
evaluation
Table 2.3
guidance on best practice
8.7
and highway management
8.4.1–8.4.7
issues
8.5.1–8.5.7
and landscape management
7.4.10
and landscaping
8.4.7
legislation and responsibilities
8.6
nature reserves and wardens
8.8.2
need for research
8.4.6
non–statutory designations
8.6.2
principal recommendations
8.10
protected species
8.6.3
responsibility for
8.4.3
safety
8.4.1
statutory designations
8.6.1
and trunk road schemes
2.4.2
verges
8.2, 8.4.2, Figure 8.1, Figure 8.5
navigation, legislation
4.5.1
net present value (NPV), and trunk road schemes
2.4.2
New Approach to Appraisal (NATA)
2.4.2, 2.6.1,
Table 2.1, Table 2.2, 3.6, Box 3.2, 7.5
New Realism
2.2.1
New Roads and Streetworks Act 1991
9.15
nickel, as pollutant
4.3.2, 5.5.2
nitrates, as pollutants
4.3.4
nitrogen oxides (NOX)
and air pollution monitoring
5.6.1
and air quality
5.1, 5.2.1, 5.5.2, 5.5.3
and atmosphere
5.4.2, Box 5.7, Box 5.12
and calculation methods
5.6.2
current situation
5.2.2
and DMRB
5.3
and European Auto–Oil Programme
2.3.3
and NAQS
Box 5.6
and trunk road schemes
2.4.2
and vehicle emissions
5.4.1, 5.7.2, 5.8.1,
Box 5.22, Box 5.23
London
Box 5.24
and vehicle and fuel standards
5.5.1
and verges
8.5.3
noise
barriers
6.6.3, 6.7, 7.3.5
building design and layout
6.6.6
calculation
6.3, Table 6.4
cuttings, tunnels and enclosures
6.6.5
and environmental and social costs of
road transport
Table 2.10
extent of problem
6.1.1, Table 6.1
guidance on best practice
6.6
highways maintenance
3.5
human response to
6.4
impact
6.1.3
indices
6.2.6–6.2.8
measurement
6.2.1–6.2.9
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Subject

Section

mitigation
6.6.3
as NATA criterion
Table 2.1, Table 2.2
nuisance
2.2.1
planning issues
6.5
recommendations
6.7
reduction
6.5.5
sources
6.1.2
and traffic management
6.6.4, Table 6.4
and transport policy
2.4.4, 2.4.2, 2.4.1
trends
6.1.3, Table 6.2
Noise Exposure Categories (NECs)
6.4.2
Noise Insulation Amendment Regulations 1988
6.5.4, 6.5.2
Noise Insulation Regulations 1975
6.5.2, 6.5.3,
6.5.4, 6.6.3, 6.6.6
noise management
6.1–6.7
noise–sensitive buildings
6.5.5, 6.6.1
non–porous quiet road surfaces
6.6.2, Figure 6.2
non–renewable materials
2.2.1
Northern Ireland
2.4.1, 3.1
Department of Environment (NI)
4.5.1
Environment and Heritage Service
3.4
Northern Ireland Assembly
2.4.1
nutrients, and GQA classification
4.5.2

O
oil, and gully pots
4.4.6
oil industry, and European Auto–Oil Programme
2.3.3
oil interceptors
4.6.5.2
and highway runoff
Table 4.3, Table 4.4,
Table 4.5
operating conditions, and emission rates Box 5.10
orchids, and cutting verges
8.7.2, 8.10
Organisation for Economic Co–operation and
Development, publication
6.4.2
Oxford Transport Strategy, and integrated
transport policy
2.6.1
ozone
and air pollution monitoring
5.6.1
and Air Quality Framework Directive
5.5.2
and atmospheric reactivity
5.4.2
current situation
5.2.2, Box 5.7
effect on verges
8.5.3
and European Auto–Oil Programme
2.3.3
and hydrocarbons
5.2.1
and NAQS
Box 5.6
recommendations
5.2.2
P
PAHs see hydrocarbons
palladium, as pollutant
4.3.2
park and ride schemes
5.8.1
parking, and vehicle emission reduction
measures
5.8.1, Box 5.23
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

parking charges, as traffic management measure
5.7.1
parking, on–street, and air quality
5.8.1, 5.9
parking policies, PPG 13
2.4.3
particulate traps
and recommendations regarding air quality
5.9
and vehicle emission reduction measures
5.8.1
particulates
and air pollution monitoring
5.6.1
and air quality
5.1, 5.5.2
and atmospheric deposition
4.4.4
and calculation methods
5.6.2
concentration level
5.4.2, Box 5.12
current situation
5.2.2, Box 5.7
and DMRB
5.3
and European Auto–Oil Programme
2.3.3
and maintenance practices
4.4.6
as pollutants
4.3.1
and trunk road schemes
2.4.2
and vehicle emissions
5.4.1, 5.7.2, 5.8.1,
Box 5.9, Box 5.23, Box 5.24
and vehicle and fuel standards
5.5.1
and water management
4.2
passenger transport
2.3.2, 2.4.1, 5.2.2
path length difference, noise barriers
6.6.3
pavement, porous
4.6.5.1, Box 4.7, Table 4.5
pedestrianisation
2.2.1
pedestrians
2.4.2, 2.4.3, Table 2.1, Table 2.2,
7.6.3, 9.12.2
peroxyacetyl nitrate, effect on verges
8.5.3
personal travel, targets for reduction in car use
2.2.1
pesticides
4.4.5, 4.5.3, 4.5.4, 8.5.2
phosphates, as pollutants
4.3.4
photochemical reactions, effect on verges
8.5.3
place, sense of, and built heritage
Box 9.1
Planning Policy Guidance Notes (PPGs)
2.4.3
PPG 1, “General Policy and Principles”,
and noise
6.5.1
PPG 12, Development Plans, and water
management
4.5.1, Box 4.2
PPG 13, “Transport”
2.4.3, 6.4.2, 6.6.1
PPG 24, “Planning and Noise” 6.4.2, 6.5.7, 6.5.1,
6.5.2, 6.6.1
PPG 15, and built heritage
Box 9.6
PPG 16, and built heritage
Box 9.6
plants
and environmental impacts
5.3
nature conservation
8.4.5
and solid pollutants
4.3.1
and verges
8.2, 8.5.1, 8.7.2
and Wildlife and Countryside Act 1981
8.6.3
see also vegetation
platinum, as pollutant
4.3.2
“Policy and Practice for the Protection of
Groundwater”
(PPPG)
4.5.4, 4.7.2
251

Subject
pollutants
atmospheric deposition
classification
sources
and water management

Section
4.4.4
4.3, Table 4.2
4.4.1–4.4.6
4.2, Figure 4.1,
Table 4.1
2.2.1

WHO guidelines
pollution
control and reduction
5.7, 5.7.1
practical measures against
5.8, 5.8.1, Box 5.23
transport policy
2.3.2, 2.4.1
pollution control
4.5.1
pollution control valves
4.5.5
pollution traps
4.7.3
polycyclic aromatic hydrocarbons (PAHs)
and Air Quality Framework Directive
5.5.2
clearance and maintenance practices
4.4.6
and Expert Panel on Air Quality
5.1
and infiltration basins
4.6.3.3
as pollutants from vehicles
4.4.1
ponds, and highway runoff
4.6.4
porous asphalt, as alternative road surface 4.6.5.2
porous pavement
4.6.5.1, Box 4.7, Table 4.5
porous quiet road surfaces
6.6.2, Figure 6.2
Prescott, John, and 1998 White Paper
2.4.1
present value of benefits (PVB), and trunk
road schemes
2.4.2
present value of costs (PVC), and trunk road
schemes
2.4.2
pricing
and 1998 White Paper
2.4.1
and environmental appraisal
2.6.2
problems, and trunk road schemes, 1998 White
Paper daughter document
2.4.2
Prohibition Notices (UKEA), and water management
4.5.1
project champion, and EMS
3.8
prosecution, role of UKEA 3
3.2
Protection of Badgers Act 1992
8.6.3
Protocol Concerning Emissions of VOCs or their
Transboundary Fluxes
5.5.3
Protocol on the Further Reduction of Sulphur
Emissions, Second
5.5.3
Public Health Act 1936, and highway authorities
4.5.6
public inquiries
7.1, 7.4.2, 7.6.2
public private partnerships
2.2, 2.4.4
public transport
and air quality
5.8.1, 5.9
availability
3.3
as NATA criterion
Table 2.1, Table 2.2
promotion of
5.7.1
and transport policy
2.2.1, 2.4.1
pulsed fluorescence
5.6.1
252

Q
qualitative indicators, and trunk road schemes 2.4.2
Quality of Freshwaters Directive
4.5.3
quality management systems, and EMS
3.4
quality partnerships, and 1998 White Paper 2.4.1
quantitative indicators, and trunk road schemes
2.4.2
quiet road surfaces
6.6.2, Figure 6.2

R
rail freight
2.4.1, 2.4.2
rail safety
2.4.4
railways
passenger services
5.8.1, Box 5.23
and transport policy
2.2.1, 2.2, 2.4.1, 2.4.4
receiving water dilution ratios
4.7.2
recreation, legislation
4.5.1
recyclability, and noise
6.7
recycled materials, increased use of
2.2.1
recycling, highways maintenance
3.5
reflection, and noise
6.6.3
reflective surfaces, and noise
6.2.9
regeneration
and importance of built heritage
9.8.3
as NATA criterion
Table 2.1, Table 2.2
regional policy, and 1998 White Paper
2.4.1
Regional Traffic Control Centres
2.4.1
regulation
and environmental impacts
3.4
environmental management systems
3.2
regulations, non–exhaustive list
Box 3.5
reinstatement, recommendations
7.7.2
remedial management, recommendations
7.7.2
remote sensing, and air quality
5.2.1
renewable energy
5.9
residential property, and noise
6.5.4
retailing, out–of–town
2.2.1
retention basins, and highway runoff
4.6.4.4,
Table 4.3, Table 4.4, Table 4.5
rhodium, as pollutant
4.3.2
Rio Earth Summit, and domestic transport policy
2.3.1
risks, highways maintenance
3.5
Rivers Ecosystem (RE)
4.5.2
road capacity
5.8.1, Box 5.23
road construction
2.2, 2.6.1
road haulage
2.2
road maintenance
2.2, Table 3.1
road markings
Box 9.5
road pricing
2.2.1, 2.4.2
road safety
2.4.2, 2.4.4, 2.4.1, Table 2.10
road surface
alternatives
4.6.5, Box 4.7
and noise
6.7
and noise mitigation
6.6.2
as source of pollutants
4.4.2
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Subject

Section

road tolls
5.7.1
road traffic, noise, see also noise
Road Traffic Act 1972
3.2
Road Traffic Reduction Act 1997
2.5
Road Traffic Reduction (National Targets)
Act 1998
2.5, 5.8.1, Box 5.23
Road Traffic Regulation Act 1984
6.5.2
road user charging
2.4.1, 2.6.2, 5.8.1, Box 5.23
road works, reinstatement after
7.4.7
roads, as landscape
7.1
roadside areas
assessment
8.7.1
cutting
8.7.2, Figure 8.3
erosion and disturbance
8.7.4
nature conservation
8.2, 8.7.3–8.7.7, 8.8,
Figure 8.4, Figure 8.5
see also verges
Royal Commission on Environmental Pollution
(RCEP)
2.2.1
runoff
4.1–4.7
rural areas
and cutting verges
8.5.1
development
2.4.3
landscapes
7.3.5
lighting
9.13.4
roads, case study
7.6.2
transport
2.4.4

S
safety
and environmental management
3.10
fencing
7.3.5
as NATA criterion
Table 2.2, Table 2.1
speed limits
5.8.1
and transport policy
2.3.2, 2.4.1, 2.4.2
trees
7.4.6
see also accidents
saftety, transport policy
2.4.1
St Edmondsbury Borough Council, litigation 4.5.3,
Box 4.3
salt
de–icing
8.5.3, Figure 8.2
as pollutant
4.3.4, 4.4.5, 4.7.3, Table 4.2
school journeys
2.4.1
schools
2.4.1, 6.6.6
SCOOT, traffic lights
5.8.1
Scotland, and 1998 White Paper
2.4.1
Scottish Environment Protection Agency (SEPA)
3.4, 4.5.1, 4.5.4, 4.6.5.2
scrub, control
8.7.3, 8.7.2, 8.10
Second Protocol on the Further Reduction of
Sulphur
Emissions
5.5.3
sedimentation lagoons, and highway runoff 4.6.2,
Table 4.3, Table 4.4, Table 4.5
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

sedimentation tanks, and highway runoff
4.6.2,
4.6.4, 4.6.4.1, Table 4.3, Table 4.4
semi–natural habitats
8.2
sensitivity, and landscape management
7.4.9
serendipity, and landscape management
7.4.9
severance
as NATA criterion
Table 2.2, Table 2.1
and trunk road schemes
2.4.2
sewerage, and highways drains
4.5.6
shipping, freight
2.4.1, 2.4.2
short sea shipping, freight grants
2.4.1
signing, improving current practice
9.13.2
Single European Act 1986
2.3.2
Single Regeneration Budget
9.7
Sites of Importance for Nature Conservation
8.6.6, 8.6.2
Sites of Special Scientific Interest (SSSIs) 2.5, 3.2,
8.6.1, 8.6.4
sleep disturbance, and noise
6.4.3
snow, and pollution
4.3.2, 4.4.5
soakaways
4.6.3.1, 4.7.3, Table 4.5
social costs, road transport
Table 2.10
social space, and townscape
9.5
sodium chloride
de–icing
8.5.3, Figure 8.2
as pollutant
4.3.4, 4.4.5, 4.7.3, Table 4.2
Sofia Protocol, and air quality
5.5.3
soil, and DMRB
5.3
solids
clearance and maintenance practices
4.4.6
as pollutants
4.3.1, 4.4.1
sound insulation
6.5.5, 6.6.3
sound insulation grants
6.5.4
sound levels
6.2.3–6.2.7
sound pressure levels
6.2.3–6.2.4
source control techniques
4.7.2
Source Protection Zones (SPZs), groundwater 4.5.4,
4.7.3, Figure 4.3
spaces, built heritage
9.5, 9.6
spectrophotometry
5.6.1
speed
and noise
6.7
traffic management
6.6.4, Table 6.3
transport policy
2.4.1, 2.4.2
vehicle emissions
5.4.1, Box 5.10
speed limits
5.8.1, 5.9
spillages
4.4.3, 4.5.5, 4.7.3
staff
3.3, 3.8, 3.9.2
stakeholders, and EMS
3.3
standards, use in environmental appraisal
2.6.2
Standing Advisory Committee on Trunk Road
Assessment (SACTRA)
2.2.1
start emissions, calculations
5.6.2
Stone Mastic Asphalt (SMA)
6.6.2, Figure 6.2
storage facilities, and highway runoff
4.6.4
storage tanks, and highway runoff 4.6.4.1, Box 4.5
Strategic Rail Authority (SRA)
2.4.1
253

Subject

Section

strategic road network
2.4.4
street clutter
reduction
9.11.2, 9.11.3, Box 9.5
conflicting objectives
9.12.1
street furniture
and built heritage
9.9, 9.13.2, 9.14.2, 9.14.1,
9.17
and landscape management
7.4.8, 7.6.1
reinstatement after roadworks
9.15
street scene, importance to built heritage
9.9
streetscape, treatment of buildings and roads 9.17
subsidiarity, and European transport policy
2.3.2
suburban areas
landscapes
7.3.4
roads, case study
7.6.3
sulphur, “city” fuels
5.8.1
sulphur dioxide
and air pollution monitoring
5.6.1
and air quality
5.1, 5.5.2
current situation
5.2.2, Box 5.7
and Helsinki Protocol
5.5.3
and NAQS
Box 5.6
surface water impact criteria
4.7.2, Box 4.8
sustainability
2.4.3, 3.3, 4.1
sustainable development
3.2
Sustainable Development Strategy
2.4.3
sustainable mobility
2.3.2
swales, and highway runoff
4.6.1, Table 4.4,
Table 4.3
symmetry, and built heritage
Box 9.2

T
tactile paving, access
9.13.3
tapered element oscillating microbalance
5.6.1
tax, vehicles
2.4.1
taxation, as value
2.6.2
technical knowledge, need for interdisciplinary
solutions
9.12.2
technology, and air quality
5.8.1, 5.9
texture, and built heritage
Box 9.4
Thin Polymer–Modified Asphalt Concrete (VTSL)
6.6.2, Figure 6.2
through–ticketing, public transport
2.4.1
titration, and sulphur dioxide
5.6.1
toll roads, and environmental impact assessments
3.2
Town and Country Planning Act 1990
4.5.1,
Box 9.6
Town and Country Planning (Assessment of
Environmental Effects) (England and Wales)
Regulations 1999
6.5.2
Town and Country Planning (Development Plan)
Regulations 1991
4.5.1
Town and Country Planning (Environmental Impact
Assessment) (England and Wales)
Regulations 1999
4.5.3
254

townscape
9.4, 9.6
tradable permits, and environmental appraisal 2.6.2
trade barriers, EMAS potential as
3.6.1
traffic calming
2.2.1, 2.4.1, 5.7.1, 9.13.5
traffic controls, and air quality
5.9
traffic density, pollution and water management 4.2,
Table 4.1
traffic equipment, as street clutter
9.11.2, 9.11.3
traffic growth, and 1998 White Paper
2.4.1
traffic lights, and air quality
5.8.1, 5.9
traffic management
and air quality
5.7.1, 5.8.1, 5.9, Box 5.19, Box
5.20, Box 5.21, Box 5.23
and noise
6.6.4, 6.7
and rural landscapes
7.3.5
and transport policy
2.2.1, 2.4.1
traffic management
and air quality research programme (TRAMAQ)
5.7.1, Box 5.19, Box 5.20, Box 5.21
traffic reduction
and 1998 White Paper
2.4.1
and air quality
5.9
traffic regulation orders
5.8.1
traffic signs
and rural landscapes
7.3.5
as street clutter
9.11.2, 9.11.3, Box 9.5
and suburban landscapes
7.3.4
traffic volume, and air quality
5.1, Box 5.1,
Box 5.23
train services, and 1998 White Paper
2.4.1
training, and EMS
3.3, 3.8
TRAMAQ see traffic management and air quality
research programme (TRAMAQ)
transformation, and air quality
5.4.2
Transport 2010
2.4.4
Transport Bill, and 1998 White Paper
2.4.1
Transport, Department of, and landscape
management
7.4.3
transport infrastructure, PPG 13
2.4.3
transport, means of, promotion of alternatives 5.8.1,
Box 5.23
transport planning, RECP report
2.2.1
transport policy
2.2–2.2.1
Transport (and Road) Research Laboratory
and noise
6.3.1
and rural roads case study
7.6.2
Transport White Paper 1998
2.4.1–2.4.3
TRANSYT, traffic lights, and vehicle emissions 5.8.1
travel demand, PPG 13
2.4.3
travelcards, public transport
2.4.1
treatment trains, and highway runoff
4.7.3
Treaty of Rome, and domestic transport policy 2.3.2
Tree Preservation Orders (TPOs) 7.3.3, 8.6.1, 8.6.5
trees
and landscape management
7.4.5
in new verges
8.7.7
non–native species
8.4.7
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

Subject

Section

optimum use of
7.7.1
planting on roadside areas
8.7.5
and safety
7.4.6
and urban landscapes
7.3.3, 7.6.1
trip matrices, and road appraisal
2.2.1
tropospheric ozone, and European Auto–Oil
Programme
2.3.3
trunk roads
and air quality
5.2.1, 5.8.1, Box 5.2, Box 5.23
and landscape management
7.2
and transport policy
2.4.4, 2.4.2, 2.4.1
Trunk Roads Maintenance Manual (TRMM),
and trees
7.4.6
tunnels, and noise
6.6.5

U
UKEA see Environment Agency (UKEA)
Ultra Thin Hot Mix Asphalt Layer (UTHMAL) 6.6.2,
Figure 6.2
ultra violet radiation
5.6.1
Underground, London, and Transport 2010
2.4.4
United Kingdom
legislation, and environmental management 3.2
responsibility for management of air quality 5.5.4,
Box 5.13
transport policy
2.4.1–2.4.4, Box 3.2
1998 White Paper
2.4.1
United Kingdom Environment Agency (UKEA) see
Environment Agency (UKEA)
United Nations
Principles of Environment and Development 1992
3.2, 3.3, Box 3.1
World Health Organisation (WHO)
air quality
2.2.1, 2.4.3
conference on environment and health
3.10
Environmental Health Criteria Document 12 on
Noise
6.4.3, 6.4.2, 6.4.5, 6.5.2
United Nations Economic Commission for Europe
(UNECE)
Convention on Long Range Transboundary
Air Pollution
5.5.3
United Nations Framework Convention on Climate
Change
5.5.3
urban areas
car use
2.2.1
landscapes
7.3.3
PPG 13
2.4.3
roads, case study
7.6.1
urea, as pollutant
4.4.5
utilities
street work
2.4.1
and verges
8.4.2

V
vegetation
T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS

and highway runoff
4.2, 4.6.4.4, 4.6.1
and landscape design
7.4.2
and landscape management
7.2, 7.4.3, 7.4.5
in new verges
8.7.7
and noise
6.6.3
non–native species
8.4.7
and reduction in impact of vehicle emissions
5.8.2
and rural landscapes
7.3.5
and rural roads case study
7.6.2
and suburban landscapes
7.3.4
and suburban roads case study
7.6.3
and urban landscapes
7.3.3
see also plants
vehicle emission standards, and European transport
policy
2.3.3, 2.3.2
vehicle emissions
and air quality
5.7.2, 5.9
as air quality issue
5.4.1
potential effect of traffic management
Box 5.21
reduction measures
5.8.1, 5.8.2
and reduction measures
Box 5.23
as source of pollutants
4.4.1, 5.1, Box 5.1
and transport policy
2.4.1, 2.4.2, 2.4.4
and vehicle’s temperature
5.6.2
vehicle fleet, and vehicle emissions
5.8.1
Vehicle Inspectorate
5.5.1
vehicle noise
6.1.2
vehicle operating costs, as NATA criterion
Table 2.2, Table 2.1
vehicle size
and emissions
5.4.1
and particulate emissions
Box 5.9
vehicle technology
2.2.1, 2.3.3
ventilation, and noise
6.6.6
verges
appropriate treatment
8.7, 8.7.1
cutting
8.5.1
case study
8.8.2
management plans
8.10
see also roadside areas
verges, special
8.7.6
case study
8.8.3
visual benefit, and trees
7.3.3
visual criteria, and noise
6.7
visual order, informal, and built heritage
Box 9.3
volatile organic compounds (VOC), and air quality
5.1, 5.5.2

W
Wales, and 1998 White Paper
2.4.1
walking, and 1998 White Paper
2.4.1
water
contingency planning
3.9.3
and DMRB
5.3
highways maintenance
3.5
as NATA criterion
Table 2.2, Table 2.1
255

Subject

Section

treatment of highway runoff
4.6.1–4.6.5
water abstraction points, and trunk road schemes
2.4.2
water authorities
4.5.6
water management
4.1–4.7
costings
4.7.1, Table 4.4
design selection
4.7.2
legislation and responsibilities
4.5, Box 4.1
recommendations
4.7.3
water quality
2.4.2, Table 2.6, 4.5.2, Figure 4.2
Water Quality Objectives (WQOs)
4.5.2, 4.5.4
Water Resources Act 1991 (WRA)
3.2, 4.5.5,
4.5.1, 4.5.2, Box 4.1
Water Supply (Water Quality) Regulations 1989
4.4.5
waterways, inland, freight policy
2.4.2
wealth creation, integrated transport policy
2.4.1
weather
and atmospheric dispersion
Box 5.11
contingency planning
3.9.3
and Gaussian Plume
5.6.2
and impact of vehicle emissions
5.8.2
and location of monitoring equipment
5.6.1
and noise
6.2.8, 6.3.1, Figure 6.1
weeds
7.4.7, 7.4.5
Weeds Act 1959
8.6.3
Westminster, City of, Strand, street furniture 9.14.1

256

wetlands, and highway runoff
4.6.4, 4.6.4.5,
Box 4.6, Table 4.3, Table 4.4, Table 4.5
wheel clampers, and 1998 White Paper
2.4.1
White Paper 1998
2.4.1–2.4.3
wildflower seed, use in roadside areas 8.7.7, 8.7.4
wildlife
contingency planning
3.9.3
and cutting regimes
8.7.2
and DMRB
5.3
and EMS
3.5, 3.6
and highway management
8.3, 8.4.5
and highways environmental management model
3.9
Kent case study
Figure 8.5
and pollutants
4.3.3, 4.3.1, 4.4.5
and roadside areas
8.2
and trees
7.3.3
and Wildlife and Countryside Act 1981
8.6.3
Wildlife and Countryside Act 1981
2.5, 8.6.1,
8.6.3, 8.7.2
wildlife trusts, and nature conservation 8.6.6, 8.10
Wilson Committee on the Problem of Noise 6.4.5
workplace parking
2.4.2, 2.4.1, 5.8.1, Box 5.23
World Commission on Environment and
Development (Brundtland Commission)
3.1
Z
zinc, as pollutant

4.3.2

T HE E NVIRONMENTAL M ANAGEMENT OF H IGHWAYS