Performance assessment of automatic vehicle location (AVL) systems

The Federal Transit Administration (FTA) considers computer aided dispatch and automatic vehicle location (CAD/AVL) systems to be an important element of their advanced public transportation systems (APTS) program. In 1992 the Denver Regional Transportation District contracted with the Westinghouse Company (now TMSI) to equip their fleet of over 800 buses with AVL, using the Global Positioning System (GPS) satellites to provide position data. The system to be installed also included CAD, which enables the dispatchers to see the positions of each bus in the fleet at all times. The FTA, through the Volpe Center, contracted with Sandia National Laboratories to perform a technical assessment of the AVL system. This paper describes both the methodology and some of the results obtained in that evaluation, which was performed in the summer of 1995, just prior to system acceptance. The evaluation looked at position accuracy under a variety of conditions, and in a variety of locations. Reliability of the data communications between the vehicles and dispatch center was measured as well.