Analysis of Cooperative Bus Priority at Traffic Signals

Transit signal priority (TSP) is an effective strategy to control bus schedule adherence, increase ride comfort, and, in turn, reduce fuel consumption. However, its provision may cause negative externalities on general traffic. In this paper, we demonstrate how coordinated in-vehicle driver advisory systems (DASs) can partly reduce the signal priority control requests. Such cooperative solution, enabled by the connectivity between vehicles and the signal control system, allows combining signal adjustments with dwelling and speed advisories. We show that combining in-vehicle advisory with signal priority can reduce stops at signals, decrease trip time when compared with TSP used alone and, in some case, achieve the same performance without resorting to TSP. In addition, we demonstrate that DASs used alone have marginal impact on trip times, hence can be applied unconditionally. A simulation-based analysis indicates that the effectiveness of a control strategy-or a combination of different strategies-depends on the bus stop placement. When it comes to reduction of stop frequency at traffic signals, speed and dwell time advisories used together deliver similar performance to an unconditional TSP with green signal extensions and recalls lasting up to 10 s.