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, where the busiest intersections see almost four buses per signal cycle. Using traffic microsimulation tomodel a succession of signal priority tactics, a reduction in bus delay by 22 s per intersection was obtained, along with a small delay reduction to general traffic. The general strategy was to provide buses with green waves so that they are stopped at most once, while also minimizing initial delay. The greatest delay reduction came from passive priority treatments, changing phase sequence, splits, and offsets to favor bus movements. Greenextension and green insertion were found to be effective in 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. The authors emphasize 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.
Abstract