Incorporating bus delay minimization in design of signal progression for arterials accommodating heavy mixed-traffic flows

Design of signal progression for arterials accommodating significant transit and passenger car flows is a challenging task, as its effectiveness with state-of-the-art methodologies often degrades with the increasing percentage of bus flows due to the inevitable mutual impedance in the mixed traffic. Conceivably, bus flows, prior to reaching a link's downstream intersection, may first experience excessive delays incurred by passenger-car queues before arriving or dwelling at a roadside stop. Those dwelling bus flows will in turn constitute a temporary lane-blockage, causing passenger cars, especially those in the rightmost lane, either to perform lane changes to interfere with neighboring traffic or to endure the excessive delay. The recently-emerged innovative design methodologies producing a bus-based signal progression system or dual-modal progression band, despite their effectiveness at the experimental level, are difficult to be supported by responsible agencies in practice unless with the policy mandate of promoting transit usage. Hence, this study proposes an alternative to facilitate bus flows by incorporating the bus delay minimization in the progression design for passenger-car flows, using the optimized offsets, phase sequences, and link progression speed. The proposed model explicitly accounts for all types of bus delays under various traffic scenarios constituting the bus entry time, bus stop location, and the patterns of passenger-car queues. The results from the extensive numerical experiments confirm that the proposed model can generate a bus-friendly signal progression plan for a wide range of mixed bus and passenger car traffic scenarios.