Operational Strategy for Advanced Vehicle Location System–Based Transit Signal Priority

Future deployments of transit signal priority (TSP) in the United States depend largely on improving TSP strategies to better accommodate transit vehicles while at the same time minimizing the negative impacts on the vehicles of the nonprioritized approaches. Advanced vehicle location (AVL) technology holds great potential in this regard. This paper develops a methodology that incorporates the predicted bus arrival time information into an AVL based TSP system to improve its performance. It is demonstrated analytically that the time to trigger the traffic signal for priority operation, especially Early Green, is of particular importance to both transit and passenger vehicles. A theoretical model is developed to identify the optimal time to place a priority call based on the predicted bus arrival time information. A simulation analysis is conducted to verify the theoretical approach and further identify the optimal call-time points for general cases. The research is focused on operation of TSP under moderately congested and congested traffic conditions wherein the concern about the adverse impact of TSP exists. It shows that in general, starting the priority operation when the bus is about $20–30\mathrm{s}$ away from the intersection produces good results for both bus and general traffic. The findings of the research can be easily integrated into an AVL based TSP system and may potentially enhance the performance of such a system.