An Adaptive Transit Signal Priority Strategy Using GPS/AVL and Wireless Communication Systems

This paper reports on a study undertaken to integrate the already-equipped GPS/AVL system on buses with an adaptive signal priority strategy using wireless communications. These communications can consider the bus schedule adherence, number of passengers, vehicle location and speed. The authors describe how the City of Minneapolis recently deployed wireless technology to provide residents, businesses and visitors with wireless broadband access anywhere in the city. They note that traditional presence detection systems, ideally designed for emergency vehicles preemption (EVP), usually send signal priority requests, after a preprogrammed time offset, as soon as transit vehicles were detected, without the consideration of bus readiness. Communication with the roadside controller for signal priority may be established using the readily available 802.11x WLAN (Wireless LAN) or the DSRC (Dedicated Short Range Communication) 802.11p protocol currently under development for wireless access in vehicular environment. The authors describe their proposed priority strategy, its evaluation using microscopic traffic simulation, and the embedded prototype systems. A traffic model of Franklin Avenue in Minneapolis, Minnesota, consisting of 22 signalized intersections, was developed, calibrated, and simulated in order to compare the measures of effectiveness before and after applying the signal priority strategy. Vehicle travel time, delay, speed and number of stops were measured to evaluate the effectiveness of the transit priority strategy. Simulation results indicate that a 12-15% reduction in bus travel time during AM peak hours (7AM-9AM) and 4-11% reduction in PM peak hours (4PM-6PM) could be achieved by providing signal priority for buses.