Impact of Bus-Only Lane Location on the Development and Performance of the Logic Rule-Based Bus Rapid Transit Signal Priority

Curb bus-only lanes and median bus-only lanes are two commonly used types of the on-street running ways of bus rapid transit (BRT) systems. Transit signal priority (TSP) has proven viable in improving transit schedule adherence and in expediting transit service and is recognized as a key element of BRT systems. From a TSP designer’s point of view, it provides a systematic analysis of the impact of bus-only lanes location on the development and performance of the logic rule-based bus rapid transit signal priority (BRTSP). As an emerging active TSP for use at isolated signalized intersections, BRTSP is centered on five categories of logic rules and can fully accommodate the variety of phase scheme. Green extension, early green, and phase insertion can be provided to prioritized vehicles within specific priority windows. The signal operations on bus-only lanes and general-purpose lanes are influenced by prioritized vehicle arrivals and departures and general traffic demands that are detected. Compared with curb bus-only lanes arrangement, median bus-only lanes arrangement imposes more restrictions on the establishment of phase combinations and phase sequences, resulting in less flexibility in assigning right-of-way at an intersection level. Among the components of BRTSP, the bus-only lanes location influences the first minimum green time calculation for vehicle phases, the walk interval calculation for pedestrian phases, the definition of priority windows, the design of logic rules, and the placement of prioritized vehicle detectors. The results of simulation experiments conducted by VISSIM under heavy load scenarios indicated the following: (1) no matter the bus-only lanes location, the phase sequence with all the through-vehicle phases defined as the initial phase had the potential to better moderate the negative effect of signal priority treatments on general traffic and pedestrians; (2)  insufficient evidence could not prove that median bus-only lanes arrangement had an overwhelming advantage over curb bus-only lanes arrangement in reducing the delays of prioritized vehicles at traffic signals and vice versa; instead, more attention should be paid to general traffic and pedestrians performance when arranging and managing the bus-only lanes; and (3) curb bus-only lanes arrangement appeared to have an advantage over median bus-only lanes arrangement in improving overall intersection performance if green extension and early green were provided to TSP-enabled intersections. To keep general traffic and pedestrians performance from severely deteriorating, phase insertion service, if desired (in addition to green extension and early green), should be provided only to intersections with median bus-only lanes in a conditional manner.