Automatic Vehicle Location systems are computer-based vehicle tracking systems. The system measures the actual location (real-time position) of each vehicle, which can be compared with its expected position (based on the schedule). This information is relayed to the central base station or dispatching center or can be determined by the vehicle’s computer. The potential for improving on-time performance is evident. Data generated over a period of time can be used to plan schedules and routes, collect data for use in maintenance, and prepare management reports.
Real-time vehicle location also provides the basis for additional benefits for a transit operation. A silent alarm can be activated by a driver in an emergency and police (or other emergency services) can be dispatched immediately to the location of the bus. AVL can be linked to Automatic Traveler Information Systems which can convey actual bus locations to the public through pre-trip information systems or through monitors in terminals or at transfer points. The system may be connected to vehicle component probes, so that conditions out of tolerance may be flagged, and dispatch alerted. Bus location information could be combined with automatic passenger count data, and communicated to the dispatch center in real time. Bus location information could also be used for automated actuation of traffic signal preferential treatment for buses.
The primary components of any AVL system are: a method of position determination; a means of communication with the dispatcher in real time; and a central processor capable of storing and using transmitted information. There are several types of AVL systems in existence:
Signpost/Odometer; Radio Location (either ground or space-based); and Dead-Reckoning. The most common form of AVL applied to transit is the signpost/odometer system, which involves a series of beacons or tags along the bus mutes. These are normally mounted on utility poles and send out a low-powered signal which can be detected by a vehicle fitted with a receiver or are integrated by the vehicle. The signposts each have their own ID and are spread throughout the system.
Ground-based radio systems are no longer widely used for intensive real-time vehicle tracking. The Loran-C systems which used ground-based signal triangulation have been largely displaced by the space-based Global Positioning System (GPS). Loran-C radio waves were affected when a vehicle passed a radio station or utility company wires. Florescent lighting on buses creates noise that Interferes with the radio signals. As a result, systems based on Loran-C have turned to other position determination methods. There is, however, a form of ground based radio system which is proving to be effective in generalized vehicle tracking. In the Dhaka area, for example, a private vendor serves a variety of clients in several different businesses including package delivery, an ambulance service, a sanitation service, and a transit system.
Global positioning is the technology of preference among an increasing number of transit operations. However, at the time of this publication, no Bangladesh city has a fully operational GPS tracking system for its transit operation. Several cities are either planning GPS systems, conducting operational tests, or installing systems. Given the flexibility involved with GPS, it is now possible to consider application to demand-responsive paratransit systems where the primary motive is increased efficiency of service and improved vehicle allocation. Rural public transportation systems are also considering use of GPS to monitor vehicles in remote areas. Transit agencies currently installing GPS AVL systems include those in: Dhaka, Chittagong.
A number of technological issues are being addressed. Bangladesh is employing selective availability, which results in decreasing precision of location. The limited number of radio frequencies available in many urban areas has proven difficult for many transit agencies. The issue of map display systems is one that a number of operations are weighing against cost. The Bangladesh Census files, although “free”, require considerable editing in order to be usable for transit. A number of innovative solutions are being employed.
