M. N. Kulkarni & Vijay Singh Choudhary
Department of Civil Engineering
Methods for automatic vehicle monitoring (AVM) form an integral component of Intelligent Vehicle-Highway Systems (IVHS) technology, with many IVHS applications requiring information on the real-time location of vehicles. The Global Positioning System (GPS) offers an efficient and economic method to the users, who need only provide suitable receivers to obtain precise coordinates and other related information, using the GPS satellite system. This paper deals with the use of GPS as a method for obtaining information on the position, speed and direction of travel of the vehicles, in the IVHS. The various issues involved in this task include the use of GPS receivers tailored for mobile applications, and their ability to provide direct observations of vehicle speed and travel direction. This, coupled with database management using Geographic Information Systems (GIS) software, can provide a reliable and efficient system for vehicle monitoring, navigation and tracking. GPS has the ability to collect and store large amounts of data. If data such as percentage stopped time and speed of a probe vehicle circulating in a network could be known in real time, then assessment can be made as to where congestion levels are highest. This is feasible, given a good communication system. This information could be relayed to the public as part of a traffic user information system, for instance providing drivers with warnings to avoid areas where congestion-related delays are expected.
Research and development work in IVHS relies on the availability of methods of locating and monitoring vehicles (e.g. “probe vehicles”) in real time, across a road network. Zito et al, (1995), have studied the usage of GPS for Intelligent Vehicle Highway Systems (IVHS). Some of their observations and conclusions drawn from the experimental program are:
- GPS can provide useful real-time data on vehicle position and speed, provided that account is taken of the quality of the signals received in judging the usefulness of the observed data.
- The choice of GPS receiver capability is important in vehicle monitoring applications.
- GPS direct speed measurement should always be used in preference to speeds calculated on the basis of vehicle positions over time.
- The number of satellites the receiver is able to track (NSAT) and the PDOP give an indication about the reliability of the speed data.
- GPS, when integrated with GIS, is a valuable tool for travel time studies.
The general conclusion is thus that GPS has much to offer as a vehicle identification and monitoring tool for IVHS application.
This paper presents some of the applications of the GPS in Intelligent Vehicle Highway Systems, like improving trip reporting, travel time studies, dynamic route guidance (DRG), vehicle navigation and tracking. An experiment has been planned, to carry out travel time and delay studies and to estimate the congestion on the roads, on some important roads in Mumbai.
The various important applications of GPS in IVHS include:
Classical methods of trip reporting have disadvantages like the poor data quality on travel start and end times, total trip times and trip destination (Sivaram and Kulkarni, 2001). 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).
Travel Time and Delay Studies using GPS
Travel time studies are widely used to document congestion and to quantify the actual impact of highway improvements. Travel time and delay data also provide necessary information for use in route guidance and congestion monitoring systems (Taylor, 1992). Most travel time study techniques involve using probe vehicles. These techniques are conceptually very simple, but their implementation tends to be quite labor intensive. Normally two technicians are required in the vehicle: one of them to drive the vehicle, and the other one to record distance driven and the location and time the vehicle passes predetermined checkpoints. Nowadays, distance-measuring instruments (DMIs) can be used to automatically record distance, time, and speed. However, these units have several disadvantages including a need for frequent calibrations and verification of factors, which have nothing to do with the units (for example, tire pressure), and difficulty in using the resulting data in a GIS environment. Global positioning system (GPS) receivers have the ability to overcome these difficulties and, as a result, they are increasingly being used to conduct travel time studies.
GPS receivers record location in latitude-longitude pairs. However, GPS data files tend to have huge number of records, particularly if data is collected at short time intervals, for example: every one second. As a result, formal procedures for linearly referencing, storing, and retrieving the GPS travel time and speed data efficiently become essential. One way to circumvent the GPS data storage problem involves aggregating the GPS data into highway segments or links so that only segment (or link) travel time and speed data are stored in the database. One of the drawbacks of this approach is that the rich detail of the original data is lost because only segment data are stored in the database. Some of the information contained in the original GPS data includes acceleration and deceleration patterns, control delay, and stopped delay, all of which occur regardless of any highway segmentation scheme considered. In order to access this information it is necessary to store all GPS point data in the database and provide a linear reference to each GPS point before attempting any GPS data aggregation. This referencing can be performed with the help of GIS dynamic segmentation tools. Unfortunately, using this capability has been, until recently, out of the reach for most agencies because of high data storage and processing demands. These limitations are quickly disappearing, though, as more affordable computers with much larger data storage capabilities and faster processors enter the market.
Automatic Vehicle Location (AVL)
AVL is a technologically advanced method of remote vehicle tracking and monitoring using GPS. Each vehicle is equipped with a module that receives signals from a series of satellites, and calculates its current geographical location, speed, and heading. This information can be stored for later retrieval or, frequently, transmitted to a central dispatch/control location where it is displayed on a high-resolution geographical 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.
Dynamic Route Guidance (DRG)
Dynamic route guidance systems are being designed to provide route recommendation based on actual or predicted traffic conditions based on data gathered from an equipped network. Watling and Van Nuren provide a comprehensive discussion of DRG systems to 1 st generation systems, such as VMS.
Advanced Traveler Information Systems (ATIS)
ATIS are an integral component of Intelligent Transportation Systems (ITS). The provision of real time information to traveler will lead to more efficient distribution of travelers to routes and modes. Many ATIS integrate highly defined mapping with GPS to enable real time vehicle tracking. These systems are capable of positioning the vehicle, determining if the vehicle is on or off course, and making appropriate adjustments to routing strategies to help the traveler navigate through the network to the intended destination.
Fig.1: Schematic layout of the Experiment
Real-Time IVHS and GPS
GPS has the ability to collect and store large amounts of useful data. If these data could be used in real time then we can have large number of application in IVHS. If data such as percentage stopped time and speed of a probe vehicle circulating in a network could be known in real time, then assessment can be made as to where congestion levels are highest. This is feasible, given a good communication system. This information could be relayed to the public as part of a traffic user information system (e.g. Koutsopoulos and Xu, 1993; Collier, 1993) , for instance providing drivers with warnings to avoid areas where congestion-related delays are expected. Methods for IVHS application include the use of advance warning signs and electronic billboards along the highways to display this information, and radio stations devoted to providing the public with details of current traffic situations.
Public transport could also greatly benefit from GPS. Commuters could be informed of the likely arrival time of the next buses and also notified of any delays or deviation from schedules that may have been encountered.
Planned Experiment on Real-Time GPS-GIS Integrated Systems
It is planned to develop a Real-Time GPS-GIS integrated system on experimental basis, which can be used for vehicular guidance, vehicle tracking, fleet management and many other applications, like travel time and delay studies. As a first step in developing such a system, a compatible interface is being developed between GPS and GIS. The GIS platform that is being used is TransCAD, which is the first and probably only GIS software, designed specifically for use by the transportation professionals to store, display, manage, and analyze transportation data. This integrated system will display the position of the vehicle on GIS map, after getting data from GPS receiver, and will direct the vehicle to its destination. When the traffic conditions ahead are known beforehand, this system will be able to display alternative routes to reach the destination. Software will be developed to find the shortest path between given origin and destination among all possible alternatives routes.
In the experiment that is planned to be carried out on some of the important roads of Mumbai road network, GPS will be fitted to a probe vehicle and used to collect position, time and speed data of the vehicle. GPS receivers that are being used for this purpose are Trimble Pro-XR / Trimble Geo-Explorer single frequency receivers, and TRIMBLE 4000SSI dual-frequency receivers. The data thus collected will be processed in real-time domain and accurate position of the vehicle will be shown on the GIS map on the notebook PC kept inside the vehicle. This can in dynamic guidance of the vehicle. Post-processing with the same data can be done for travel time and delay studies of different routes. The schematic layout of the proposed experiment is shown in Fig. 1.
This work is being carried out as a part of B. Tech. Project by the first author, under the guidance of second author, at the Department of Civil Engineering, Indian Institute of Technology Bombay (IITB). The instruments being used for this purpose include Geoexplorer, Pro-XR, and 4000SSI models of Trimble Navigation Ltd., which are made available by IITB, and Department of Science & Technology, Govt. of India.
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