Hybrid Signal Priority and Full Actuation for Isolated Large Four-Leg Circular Intersections

Abstract

In cities with bus rapid transit (BRT) systems, median bus-only lanes (MBLs) may extend to a circular intersection of two arterials. Making the MBLs traverse the central island is advantageous to BRT vehicles with less damage to the aesthetic advantage of the circular intersection. Hybrid signal priority and full actuation (HySOFA) is developed for isolated large four-leg circular intersections with MBLs. The objective of HySOFA is to expedite the operating speed of BRT vehicles with little negative impact on general vehicles. With appropriate application of transit and traffic facilities, the central island is traversable to BRT vehicles and the right-of-way is assigned in an upgraded version of the concurrent entering mode. Traffic detectors are placed at specific positions to detect BRT vehicle arrivals and sense general vehicle demand. Signals for general vehicles are fully actuated. Green extension, early green, and phase insertion are incorporated into the fully actuated logic. According to the simulation results during peak periods, HySOFA was quite effective in reducing the delay and number of stops for BRT vehicles at the circular intersection. The resulting cost to general vehicles was not large. After implementation of HySOFA, the circular intersection outperformed its conventional intersection alternative in serving general vehicles and pedestrians with less delay. BRT vehicles would not perceive substantially less delay and number of stops at the conventional intersection than at the circular intersection. When the MBLs extended to a large four-leg circular intersection, it would be a sensible decision for traffic engineers to make traffic improvements on the circular intersection instead of converting it to a conventional intersection.