Control Strategies for Transit Signal Priority Systems
Investigators:	Dr. Francois Dion, Dr. Ghassan Abu-Lebdeh and Mohammad Ghanim, Department of Civil and Environmental Engineering

Transit signal priority measures attempt to facilitate the movements of buses across signalized intersections through temporary traffic signal timing adjustments. The two main adjustments considered include extension of a green phase, to avoid a bus being stopped by a red signal, and early green recall, to reduce the delays incurred by a bus that is already stopped. Signal timing adjustments can be sought to reduce overall travel times, improve schedule adherence or provide more regular vehicle arrivals at bus stops.

While the concept of transit signal priority has been around since the 1970s, significant changes have occurred in traffic signal control over the past 30 years. As an example, traffic signal control has evolved from simple 2-phase control to multi-phase actuated and real-time control in which the traffic signal operation is directly affected by sensed traffic conditions around controlled intersections. These changes were essentially enabled by advances in traffic monitoring and computerized traffic control algorithms. Despite these changes, most transit signal priority systems still require that traffic engineers specify which phase from which the green signal can be taken away to allow green signal extensions and early recalls to be offered on another phase. However, current traffic monitoring technologies and computer-based traffic signal may allow more flexibility in deciding from which phase the required green time should be taken away.

The objective of this research is investigate how current traffic monitoring capabilities and optimization algorithms such as genetic algorithms and neural networks can be used to determine the best operational strategies for transit signal priority along coordinated urban arterials. This means evaluating whether priority should be awarded, and if so, what would be the best signal timing strategies to attain the desired objective (reduce delay, control schedule adherence, control bus interarrival times) given the need to maintain adequate traffic signal coordination and respect various operational constraints.