Providing Bus Priority at Signalized Intersections with Single-lane Approaches

Abstract

Signalized intersections often represent a major source of bus delays. One typical strategy to mitigate this problem is to dedicate an existing car lane for bus-use only to minimize the interactions between cars and buses. However, this is physically impossible at approaches where only a single travel lane is available for each direction. To this end, this research explores a novel method to provide priority to buses at signalized intersections with single-lane approaches through the use of additional signals in a way that (nearly) eliminates bus delays while minimizing the negative impacts imparted to cars. Using these signals, the bus can jump a portion of the car queue using the travel lane in the opposite direction.This paper theoretically quantifies the delay savings buses can achieve, and the negative impacts imparted onto cars when this pre-signal strategy is applied. The negative impacts are measured as the additional car delays experienced when the intersection signal is under-saturated, and the reduction in car-discharge capacity when the intersection signal is over-saturated. In the under- saturated case, the results show that moderate average bus delay savings (∼5-7seconds per vehicle) are achieved if the pre-signal is always in operation; and these results decrease the total system-wide delay (measured in person-hours) only if bus occupancies are very high. However, if the pre-signal operation is targeted to only provide priority to the buses that would benefit the most, significant bus delay savings can be achieved (delay benefits to buses which receive priority are about doubled) while also reducing the system-wide delay, even if the ratio of bus to car occupancy is relatively modest (greater than about 20). In the over-saturated case, bus delay savings can be much more significant than under-saturated cases (greater than 30seconds per bus), and this delay saving can increase further for longer block lengths (greater than 100 m). However, the capacity of the intersection decreases by up to 25% during each cycle in which a bus arrives to the intersection. Simulation tests confirmed that the general trends and magnitudes of bus delay savings and negative impacts to cars hold for more realistic behaviors. The overall benefits are slightly smaller in the simulations, but nevertheless the strategy seems promising as a bus priority strategy at intersections with single-lane approaches in the field.