Signal Priority near Major Bus Terminal

Abstract

Near major bus terminals, multiple bus arrivals per signal cycle and a convergence of buses from conflicting directions can make it impractical to apply signal priority logic that attempts to interrupt the signal cycle for each bus. This research explores signal control logic for reducing bus delay around a major bus terminal in Boston, Massachusetts, where the busiest intersections see almost four buses per signal cycle. With a traffic microsimulation to model a succession of signal priority tactics, a reduction in bus delay of 22 s per intersection was obtained, with no significant impact on general traffic. The general strategy was to provide buses with green waves, so that they are stopped at most once, coupled with strategies to minimize initial delay. The greatest delay reduction came from passive priority treatments: changing phase sequence, splits, and offsets to favor bus movements. Green extension and green insertion were found to be effective for reducing initial delay and for providing dynamic coordination. Dynamic phase rotation, from lagging to leading left, proved less effective. Cycle-constrained free actuation, in which an intersection has a fixed cycle length within which two phases can alternate freely, provided flexibility for effective application of early green and green extension at one intersection with excess capacity. Emphasis is given to the approach of providing aggressive priority with compensation for interrupted phases, highlighting the compensation mechanism afforded by actuated control with snappy settings and long maximum greens.