Impact of Phase Scheme on Development and Performance of a Logic Rule-Based Bus Rapid Transit Signal Priority

Abstract

Focusing on isolated signalized intersections with four approaches along arterial median busway, a logic rule-based bus rapid transit signal priority (BRTSP), aiming to speed up bus rapid transit (BRT) service with less negative impact on general traffic, is developed based on a phase scheme including two BRT phases, eight vehicle phases, and four pedestrian phases. Two attributes for each vehicle phase, i.e., initial phase and terminal phase, are introduced to analyze the principles of potential phase sequences. Check-in and check-out detectors are placed on the busway to detect BRT vehicle arrivals and departures. Inductive loop detector is placed on each lane of the vehicle phase to monitor time headway(s) on a lane-by-lane basis. All the components of BRTSP can accommodate the variety of phase scheme. The minimum green time of the vehicle phase and the walk interval of the pedestrian phase are calculated cycle by cycle. In case of a BRT vehicle arrival or departure, a priority request either for green extension or for early green may be generated or cancelled by rules for priority request generation. Rules for phase transition can manipulate phase transition durations and avoid intergreen time violations. Using a binary choice approach, rules for green duration adjustment and rules for barrier crossing can serve the priority requests and adjust the green duration of each vehicle phase in an acyclic manner. Simulation experiments conducted by a microscopic, behavior-based multipurpose traffic simulation program indicated that (1) for the phase sequences where the through vehicle phases concurrent with the BRT phases were specified as the terminal phases, the left-turn vehicle phases adjacent to the BRT phases were not recommended to serve early green request in heavy load scenarios; (2) the phase sequence with more through vehicle phases being specified as the initial phases had the potential to enable BRTSP to yield better intersection performance.