The Global Positioning System (GPS) is a U.S. space-based global navigation satellite system. It provides reliable positioning, navigation, and timing services to worldwide users on a continuous basis in all weather, day and night, anywhere on or near the Earth which has an unobstructed view of four or more GPS satellites
A Geographic Information System (GIS), or Geographical Information System, is any system that captures, stores, analyzes, manages, and presents data that are linked to location.
GPS-GIS integrated systems for transportation engineering
C. M. S. L. Sivaram1, M. N. Kulkarni2 Department of Civil Engineering I. I. T. Bombay, Mumbai-400 076 Tel: 91-022-5767308, Fax: 91-022-5767302 1 [email protected]
, [email protected]
Abstract: Spatial data is the crucial component of a GIS. The important sources of spatial data are the already existing digital files, maps, which can be digitized, and more recently GPS. GPS (mapping type receivers) can be used to map an area and the data can be converted into GIS compatible forms. GPS-GIS integrated systems have some important applications in the field of Transportation engineering. These applications include vehicle tracking system for fleet management, vehicle navigation systems, and network travel time studies. GPS-GIS integrated systems can be used to predict the parameters in the car following theories, improving the trip reporting procedures. The present paper gives some details of these applications and in particular the application of GPS-GIS integrated systems for network travel time studies, which areuseful for quantifying congestion in terms of various parameters. An experiment is also planned for finding the travel time on some of Mumbai's roads. The results of this experiment are expected to be presented in the Conference. Introduction Transportation data is usually associated with spatial data, like traffic counts from particular sites, the traffic volumes along particular roads or links, etc. (Taylor et al, 2000). Geographical Information System (GIS) can be used as a database for storing transportation data. The primary advantage of using GIS as a database for transportation data is the fact that GIS can integrate the spatial data and display the attribute data in a user-chosen format. The chief sources of spatial data are the existing digitized files (e.g.: Topologically Integrated Geographic Encoding and Referencing (TIGER) files in the US). The Global Positioning System (GPS) is widely being used as a tool for collecting the spatial data. Systems which chiefly use GPS as a spatial data source for a GIS are called as GPS-GIS integrated systems. The use of GPS-GIS integrated systems in transportation engineering are described below. An experiment is planned to find the travel time on some of Bombay's roads and hence to estimate the congestion on the roads. The results of this experiment are expected to be ready for being presented in the Conference.
Applications In this section, the various applications of GPS-GIS integrated systems in transportation engineering are described. Vehicle tracking systems Vehicle tracking systems are usually used for managing a fleet of vehicles. The vehicles of a fleet are fitted with GPS, which usually transmit the positional data of the vehicles to a central station. The central station is a monitoring station, where the position of vehicles is displayed on a GIS map. Vehicle tracking systems will be useful for the police and emergency response services. The central station usually diverts the vehicle nearest to the site, where the vehicles are required. By using a wireless phone service or cellular phone network, real time corrections can be sent to the receivers fitted on the vehicles and better results can be obtained. Vehicle navigation systems Vehicle navigation systems are used for guiding vehicles to their destination. These systems usually use GPS or inertial navigation systems or a combination of both for positioning the vehicle. The advantage of using both inertial navigation systems and GPS is that navigation can be continued even when the GPS cannot receive the signals form the satellites due to obstruction. In countries like the US, vehicle navigation systems are used for guiding tourists to different tourist spots. The vehicle navigation systems use a computer, which determines the position of the vehicle, plans the route and gives the directions to the driver. The driver gives the location of his/her destination while starting his journey and the computer guides the driver by giving either audio or and visual instructions. The route the computer plans is usually optimized route; the route is the route optimized for distance or the route can be the most or the least used route (Jurgen, 1998). The above-described applications are a part of the intelligent transportation systems, where the vehicles are navigated and help is provided to the vehicles, which are stranded due to some problem with the vehicle or any accident. Zito et al, (1995), have studied the usage of GPS for Intelligent Vehicle Highway Systems (IVHS). Much of the research and development work related to IVHS (presently it is known as intelligent transportation systems or ITS) depends upon the reliability of the methods used for locating and monitoring vehicles. Some of their observations and conclusions are: 1. GPS receivers, which have the capability of displaying the speed, will be useful for determining the speed of the vehicle, even though the display might show a non-zero value of speed sometimes, when the speed of the vehicle is zero. 2. The number of satellites the receiver is able to track (NSAT) and the PDOP give an indication about the reliability of the speed data. It was found that the error in speed increased when the PDOP values were high (greater than three) and the NSAT value was three. 3. GPS, when integrated with GIS, is a valuable tool for travel time studies.
4. The conclusion that they gave was: GPS stands ready as a valuable tool for IVHS applications, given adequate attention to its possible shortcomings. Though, the above conclusions were drawn when Selective Availability (S/A) was on, these conclusions are still relevant and valid. Car following analyses The basic assumption in car following theories is that the speed and acceleration of a car are dependent upon the vehicle immediately preceding it (in a single lane of traffic). The General Motors Corporation has done some extensive studies of car following behaviour. They have used two-vehicle platoons to estimate driver behavioral responses. The Louisiana State University (LSU) has developed a new technique; it had used GPS to record aspects of vehicle motion, independently, for vehicles under open roadway conditions. A GIS was also used as tool for the creation of mapped road networks, route analysis and linear referencing. The study involved the use of GPS and GIS to collect and process vehicle movement information. In the system used by the LSU researchers, latitude and longitude coordinate information as well as speed and time data for test vehicles were collected independently. These data were reduced and translated using a GIS linear referencing technique to prepare a set of movement data for each vehicle. The study conducted at LSU has shown that GPS was a viable and valuable tool for the collection of vehicle movement data. The research conducted at LSU has allowed the results of General Motors to be expanded and the results to be further verified through the use of open roadway car following data. They have also found that the price-to-accuracy afforded by GPS was also one of its significant advantages (Wolshon and Hatipkarasulu, 2000). GPS for trip reporting The problems with the existing methods of trip reporting procedures are: the poor data quality on travel start and end times, total trip times and destination locations. A project study was conducted in Lexington, Kentucky in fall, 1996 where GPS was used to capture vehicle-based, daily travel information. The project used a computer for computer-assisted self-interviewing, combined with GPS system. Though the design of equipment required the respondents to actively turn the computer on each time they made a private vehicle trip, the GPS component could capture the "actual" travel rather than the self-reported travel. The driver had to actively select the driver and passenger names, and their trip purposes. The GPS component captured date and time, and latitude/longitude data every three seconds when a trip had begun, so that the trip start and end times were passive data elements to the respondent. The advantage of passive data recording is that respondent burden is minimized and the travel times and distances that were collected represent the true picture about the length and duration of the trip. The usage of computer for computer-assisted-self-interviewing has helped to capture data regarding trip purpose and vehicle occupancy. Having the data regarding the trip purpose, occupancy, together with the route choice and travel speed, would provide planners with the information that could be used in evaluating management systems, designing ITS, etc. To further reduce the burden on the driver, GIS can be integrated with GPS. The GPS
data, after exporting to a GIS can be viewed on the map. The use of GIS helps in knowing the destination of the trip, without the driver intervention, and also in knowing the particular route the driver had chosen to reach his destination. Though GIS has not been used in the research mentioned above, its usage for the trip reporting purpose will definitely improve the trip reporting procedure (Murakami and Wagner, 1999). Network travel time studies Moving observer methods are commonly used for travel time surveys. In this method, the observer travels in a vehicle, which is a part of the traffic stream and notes the time required for the vehicle to travel between two specified points. The problem with the moving observer method is that to get a representative value of the travel time, different drivers should repeat the method. Another disadvantage of this method is that the exact variation of the speed of the vehicle along the link cannot be studied. The variation of the speed of the vehicle along the network gives an idea about the traffic conditions on the road. Therefore, the moving observer method cannot be used for studying the localized traffic effects. Some of these effects can be overcome by using GPS-GIS integrated systems. Quiroga and Bullock (1995) have deduced the following, after performing experiments and collecting over 3 million GPS data points over a network of more than 300 miles. They have shown that to detect localized errors, the segment (the road networks are divided into segments whenever particular attribute changes, one such attribute may be the number of lanes on that segment) lengths of the road network should be around 0.2 to 0.5 miles. A sampling rate of 1 or 2 seconds is preferable and the sampling rate should be smaller than half the shortest travel time associated with the segment. In conducting travel time studies using GPS and GIS, the first step is to obtain a good base vector map with links to a database. It is advisable to construct the base map directly form GPS data, GPS data collected during future travel time studies is guaranteed to match the vector base map with in a tolerance defined by the GPS equipment positional accuracy. The major advantage of using a base map produced by a GPS, against previously existing maps is that the positional errors in the existing maps can be overcome. This new automated procedure provides consistency; fine levels of resolution and better accuracy in measuring travel time and speed than traditional techniques. For detecting localized effects in traffic, detail speed-time or speed-distance profiles along the link are required. These profiles can be easily plotted in a GIS. The travel times obtained can be used to quantify congestion in terms of parameters like delay and congestion index. Delay is defined as the excess travel time above the minimum (free flow) travel time needed to traverse a network element. Congestion index (CI) is defined as total delay divided by the free flow travel time. Congestion index is a dimensionless quantity, and can be used for comparing the congestion levels on two or more roads, as it is independent of route length, route geometry or intersection control and capacity factors that may distort comparisons of actual travel times and delays at different sites.
To alleviate the problem of congestion, Congestion Management Systems (CMS) needs to be developed. A typical CMS usually collects the travel time data and the congestion parameters are calculated as explained in the above paragraph. The congestion parameters indicate the level of congestion on the roads and necessary control measures can be taken to reduce the congestion. Planned Experiment In the experiment that is planned, GPS will be fitted to a probe vehicle and used to collect position, time and speed (of the vehicle) data. The GPS receiver that will be used for this purpose will be Trimble Pro-XR and the GIS software that will be used is TransCAD. TransCAD is the first and only GIS software, designed specifically for use by the transportation professionals to store, display, manage, and analyse transportation data. The Trimble Pro-XR receiver can collect Differential GPS data from the radio beacon at the Mumbai port, so higher accuracy can be obtained After collecting the data, it will be linearly referenced in TransCAD. The linearly refernced data can be displayed either on the already existing map or can be used to create a new network. The advantage of creating a new map is that the same map can be used in the future for travel time studies. The errors will be reduced if the same map is used. After the data management, a module in TransCAD will be developed, which calculates the travel time on a particular link. The travel time is the difference between the entrance time and exit time on the link. These times can be found out by interpolating between the two time tags, which are close to the entrance or exit of the link. Once the travel times are obtained, the congestion parameter CI can be used to calculate the congestion on the roads. The results of this experiment are expected by the end of January. Reference 1. Jurgen, R. K. 1998, Navigation and Intelligent Transportation Systems, Pennsylvania: Society of Automotive Engineers, Inc. 2. Murakami, E. & D. P. Wagner, 2000, Can using Global Positioning System (GPS) improve trip reporting?, Transportation Research -C, 7C: 149-165 3. Quiroga, C. A. & D. Bullock, 1995, Travel time studies with global positioning system and geographic information systems: an integrated methodology, Transportation Research-C, 6C : 101-127 4. Wolshon, B. & Y. Hatipkarasulu, 2000, Results of Car following Analyses Using Global Positioning System, ASCE Journal of Transportation Engineering, 126: 324-331 5. Zito, R., D'este, G., & M. A. P. Taylor, 1995, Global Positioning systems in the time domain: How useful a tool for Intelligent Vehicle-Highway systems?, Transportation Research-C, 6C: 193-209
Introduction Current methods of assessing routes taken during active transport rely on subjective recall of trip length and barriers encountered enroute or the utilization of objective measures (Geographic Information Systems –[GIS]) that may not represent actual travel patterns. This study examined the utility of Global Positioning Systems (GPS) to measure actual routes taken compared with GISestimated travel distance and barriers encountered. Methods Comparisons between GPS and GIS routes were performed for 59 of 75 children who wore a GPS during the journey to school on a single occasion. Home and school addresses were reported by parents and geocoded in GIS. Children were provided with a GPS and were instructed to travel their normal route to and from school. Data were collected between March and November 2005 and exported to the GIS to determine travel distance, number of busy streets crossed, and the ratio of busy streets to the total streets traveled on. Data analysis was performed in August 2006. Results No differences were observed between GPS-measured journeys to and from school on any of the examined variables. No differences were observed between GIS and GPS measures of travel distance (p>0.05). GIS-estimated travel routes crossed a significantly (p<0.05) higher number of busy streets (GIS: 1.68±0.12 vs GPS: 1.19±0.11) and traveled on a higher ratio of busy streets to total streets traveled on (GIS: 0.46±0.03 vs GPS: 0.35±0.04) (p<0.05) compared with GPSmeasured actual travel routes. Conclusions Geographic Information Systems provides estimates of travel distance similar to GPS-measured actual travel distances. Travel routes estimated by GIS are not representative of actual routes measured by GPS, which indicates that GIS may not provide an accurate estimate of barriers encountered. The continued use of GPS in active transport research in encouraged.
Road Transportation Management using GIS - vehicle routing and tracking
Roads are main arteries of modern society’s infrastructure, contributing heavily to the distribution of goods and persons. GIS provides many helpful applications for ensuring a smooth flow, by aiding design, routing, traffic control and real-time navigation. In essence, a GIS application in transportation is maybe no longer a GIS, but a merger of GIS with Intelligent Transportation Systems or Transport Telematics, where GIS no longer exists as a stand-alone product. Husdal, J. (1999) Road Transportation Management using GIS – vehicle routing and tracking. Unpublished working paper. University of Leicester, UK. Available online at http://husdal.com/1999/11/14/road-transportation-management-using-gis-vehiclerouting-and-tracking/ (Last accessed on [date]). Introduction Using GIS in the field of transportation opens up a wide range of possible applications, as diverse as the field of transportation itself. Whether these are cars and trucks along a road, trains along a track, ships across the sea or airplanes in the sky, all applications have one thing in common: They are objects that move along a path in space. A GIS can provide a valuable tool for managing these objects in a spatially referenced context, viewing the paths as a transportation network. This essay will attempt to display the extent of existing GIS applications within road transportation, and critically assess their appropriateness and potential. Planning and design GIS provides a valuable tool in the process of planning and designing roads. This is closely related to the term Computer Aided Design (CAD), but it is hard to tell at what level of detail CAD stops and where GIS actually begins. Modern software (e.g. Bentley’s Microstation) tends to bridge this gap between discipline-specific applications and GIS in a way that they are fully integrated. A GIS can help visualise and communicate the effects of roads on their environment. Engineering drawings and maps may evoke a vivid landscape in minds of engineers familiar with them, but to decision makers or the public in general these drawings can be quite incomprehensible. Traditionally, displaying different route options and proposals has been done in the form of 2D maps, assisted by section drawings, maybe together with an aerial photo, where the road network was overlaid in the form of lines. It is simple and straightforward, but it is not conveying much information on the actual impact.
Therefore, the UK Highways Agency has taken on building virtual showrooms, presenting the road by displaying a 3D drive-through along a highway or a bird’s eye view of the landscape from any angle the user wants to hover (Sinclair, 1999). This can be presented to a planning board or the public using ordinary PCs, or it can even be published on the Internet for open access to everybody. The highways agency in the French department de la Loire has been using GIS since 1989 for many purposes: Traffic accident patterns are visualised and safety improvements are made where they are most needed. By collecting significant data for the whole network, repairs and works budgeting have become more reliable and calculated in advance. First creating the optimal route between locations and then using GIS to decide how and where to sign, improved directions and movements in the road network and helped avoiding congestion (Marshall, 1995). Routing
Euler’s famous “Königsberg bridge” question, dating back as far as 1736, is often seen as the starting point of modern route finding – was it possible to find a route through the city crossing each of its seven bridges once and only once and then returning to the origin? His methods formed the basis of what is now known as graph theory, and paved the way for path finding algorithms that are applied in GIS in the solution of routes in transportation networks (Rimsha, 1996). Hence, in GIS route planning is often referred to as network analysis. Route planning is one of the most popular applications within transportation, for obvious reasons. Roads are part of the infrastructure that makes up the spinal cord of modern society, but roads can just as easily turn into bottlenecks. Consequently, any business deploying vehicles is interested in determining which route is the best to follow as means to save time and essentially gain the best cost/benefit ratio. This can be used to distribute goods, deliver newspapers or pizza, respond to emergency calls, or to plan your personal travel. There are many ready-made software products available on the market, ranging from simple A-to-B drive time analyses to full-fledged fleet management systems. There are also many online routing applications available on the Internet, allowing travellers to log in, plan their journey and consider different options. Route planning is also applied as apart of location planning, analysing catchment areas for different sites, calculating overall drive-times to and from site, maximising potential customer inflow and ensuring best possible accessibility. Safeway has successfully implemented GIS for such planning (Fletcher, 1999).
Navigation Route planning in advance of a journey is one way to enhance transportation management. Using an in-car navigation system is another one, and has been on the market for some time. Blaupunkt introduced its Travel Pilot as early as in 1989. In 1997, ETAK, a leading provider of digital map data and pioneer in navigation software, released a map database providing turn-by-turn vehicle navigation throughout mainland Great Britain. Used in conjunction with GPS this system not only is an in-car route finder, but also provides the driver with detailed instructions on where to turn in what direction. It also contains a lot of information on points of interest a driver might want to know. The road data itself derives most in most cases from Ordnance Surveys OSCAR product family, which is then used by different manufacturers in conjunction with their own system. Tracking
Not only is finding the best way from A to B of importance to vehicle drivers or the company who deploys them. To keep track of where the vehicle is at any given moment of time is equally, if not even more crucial, in efficient fleet management. Tracking and monitoring of vehicle movements emerged with the advances in mobile communication (GSM) and satellite navigation (GPS). The position of a vehicle is monitored via onboard GPS, transmitted back to a base via GSM, and loaded into a GIS where it can be displayed on map. Already in 1995, Oslo Taxi of Oslo, Norway, fully automated the monitoring of its entire fleet (Baumann, 1995). The exact location of all vehicles is now known at all times by the taxi dispatchers, improving any needed emergency response to the driver and customer response to incoming orders, ensuring that the nearest available taxi is sent to the pickup location. Around 400,000 vehicles are stolen each year in the UK. With an in-car GPS that continuously relays the car’s position to a control centre, the car can easily be tracked in case it is stolen. In case of an emergency breakdown, help can be dispatched to his or her exact location. (Fitzgibbon, 1999). Traffic control The Highway Agency in the UK and many other countries monitor ongoing traffic at critical points in the road network round-the-clock, using cameras, counting devices or other means of traffic data gathering, and then relaying this information to the public or using it for analytical purposes.
Traffic control systems are among the most demanding of the Intelligent Transportation Systems. They may have to cover large geographical areas and interface with a large number of devices, thus managing data available from a variety of disparate sources, not necessarily in common format. (WS Atkins, 1999) Metronet works is a private UK company that specialises in relaying traffic information, giving up-to-date real-time traffic information to the public, to be broadcasted via radio or to be displayed on the Internet. Southampton has implemented a EU-funded project, ROMANSE. In this project, relevant up-to-date traffic and travel information for public and private transport users is posted electronically on touch screen displays at main transport interchanges, shopping centres, tourist information centres and libraries, and also on the Internet./p> Trafficmaster is a company in the UK that has been going its own way, installing a network of traffic flow sensors along major road arteries, and relaying this information to subscribing motorists via mobile phone or in-car voice device. (Fitzgibbon, 1999) Evaluation Using GIS aiding road design has proved itself as useful, especially when visualising impact on the environment is concerned. Conflicts that arise can be seen directly, and different options can be explored more easily than on a paper map. Using GIS for 3D visualisation may also help solving clashes that often occur when different engineering fields work together on a large-scale project. Changes in design can be made before the problem manifests itself on site. A further development of this application could be for use in simulators for training drivers, similar to simulators already in use for planes and ships, something that could turn out to be especially helpful for emergency vehicle drivers when they are still new to an area. In all the mentioned applications GIS is a tool for visualising and analysing data. This is historically speaking the generic way of describing a GIS. The data itself has to be compiled and put together in databases that are linked with or resident within the GIS. Looking at future prospects, the potential range of such applications, combined with 3D visualisation, is virtually unlimited. Route planners are very useful tools in general, but they have limitations. Data that is used in route-planning systems must be extremely accurate. Even though the road network may look fine on screen, it may contain false information that will divert the route from where it should go, such as sending a vehicle the wrong way down a one-way street or using a route that is closed to the public. The data must be kept up-to-date with the latest status of any particular road in the network. Thus, a GIS for route planning will have to contain a large volume of attribute data, depending on the specific application needs. Users may want to enquire about
gradients, height and weight constraints, road works, filling stations, detour options, hotels or other points of interest (Rimscha, 1996). All this has to be updated continuously. This again means cost for the end user. This is not a product you buy once and for all. Route-planning systems typically either calculate the shortest or the fastest journey, leaving the user to make the choice. In doing this, the system uses algorithms for choosing a particular route. However, some experienced drivers may not take the same route as the system calculates. For inexperienced drivers, on the other side, the system provides much help. Route planners will often tend to generalize, because variables such as time of day, weather conditions (e.g. sun, rain, fog, ice or snow), type of car used or driver behaviour are usually not implemented, even though they lay heavy influence on driving. Systems may also lack local knowledge a driver has about a certain stretch of a route. Given the weight that road transport has in distributing goods and personal transport, and given the steadily increasing complexity of road networks, route planners will undoubtedly not cease to exist. As for in-car navigation systems, European legislation on what may be displayed inside a moving vehicle is rather rigid, only allowing a screen showing a single bold arrow (Schofield, 1996). A full map can only be displayed when the vehicle is still. Voice messaging has no such restrictions. Both visual and audio output have a potential for distracting the driver, which is why the newly revised Highway Code includes an admonition against the careless use of route guidance and navigation systems. Bearing in mind the current debate in Europe over banning the use of mobile phones in cars, in-car navigation may face the same argument. Tracking systems depend on GPS for finding the exact location of a vehicle. Modern GPS receivers have an accuracy of between 3 and 30 metres in good conditions. Using so-called differential GPS, the accuracy can be increased to a few centimetres. With a moving object, this is more difficult. Curiously enough, none of the manufacturers advertising their navigation systems on the Internet sites that are listed as reference actually mention the accuracy or possible deviation of the system. On large-scale maps this will seldom generate a visual error, even when roads may be slightly displaced on the map to create a clearer distinction between roads or to highlight certain features along the road. One aspect that needs to be mentioned is the fact that in-car navigation also can serve as a tracking device, leaving behind electronic signals of a vehicle and its whereabouts, adding up just another of the many electronic footprints a person might activate during a day. The range of products and applications in the transportation sector indicates that these are tools that are in high demand. It has been estimated that some 80% of all information that
any business manages has a geographic context (Leslie, 1999). Crucial to any organisation’s success is access to good and valid information. In the field of transportation much of this information is constantly moving, thus increasing the demand for up-to-date information. GIS can help manage this information. Conclusion
The applications listed have been described as applications of GIS, and may in their consecutive order also be read as how GIS in transportation has developed over time. Looking closer, the latter ones are actually more related to the term transport telematics than to GIS. Transport telematics means the large-scale integration and implementation of telecommunication and informatics technology in the field of transportation, penetrating all areas and modes of transport, the vehicles, the infrastructure, the organisation and management of transport (Wähl, unknown). Transport telematics is also often referred to as being part ITS. Consequently, it is hard to distinguish between GIS and ITS. The more sophisticated an application is, the more seamless the merge is between different integrated systems. It has been shown that using GIS in transportation calls for very high accuracy on the attribute data of the road network. With the number of different software brands on the market, a careful examination of the provider’s ability to supply and update correct data is important for the success of the application. It is clear that GIS can be used for a wide range of applications in the transportation sector. Merging GIS with telematics seems to open up a whole new array of possible realtime applications in the transportation sector. What all these applications have in common is that GIS plays a major part, providing the spatial reference, but can the system still be called a GIS application? It may be argued that this system is no longer GIS, but a technology that dissolves GIS into something new. This is probably the largest potential for the future of GIS in transportation: GIS will no longer be a stand-alone product, but fully integrated with other business information systems.