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.
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.
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:
- 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.
- 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.
- GPS, when integrated with GIS, is a valuable tool for travel time studies.
- 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.