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Pedestrian Crossing Caused Signal Transition Study
Civil and Environmental Engineering
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Traffic signal coordination is generally applied to improve traffic efficiency on arterial roads. In traditionally coordinated signal systems, signal transition may reduce traffic operational efficiency, causing extra number of stops on the main-street and extra delay for both the main-street and side-street. One of the most common events that cause signal transition is a signal timing plan without accommodating pedestrian crossing. When a traffic signal timing strategy does not accommodate pedestrian crossing, it allows shorter phase splits than the minimum green time for pedestrians crossing the main street. The crossing street green time is extended to meet the requirement of minimum green for pedestrian when a pedestrian pushes the crossing button. In this case, the signal coordination will be interrupted. It generally takes 1-3 cycles for the signal to go back to coordination after the pedestrian interruption. Previous studies have been focusing on the fundamentals of transition algorithms associated with time-of-day transition and emergency vehicle preemption. However, the transition impact due to un-accommodated pedestrian crossing, which can be minimized by using appropriate transition algorithms, has not been explored thoroughly.This research first reviews the transition algorithms and summarizes them into three categories. Qualitative analyses are then conducted on how coordination bandwidth and main-street delay are affected by pedestrians under three categories of transition algorithms. The analyses are conducted using the HILS tool based on a real-world arterial. Two types of controllers – Eagle EPAC300 controller and Naztec 981 TS2 controller – are tested in the analyses. The study compares the main-street number of stops and delay under various scenarios, with a wide range of affecting factors, including pedestrian call frequency, V/C ratio, transition algorithm, and phase split difference. The results indicate that the Subtract and Add algorithms perform most efficiently for under-saturated and over-saturated conditions, respectively. The benefit of Subtract transition algorithm is more significant with lower degree of saturation. However, when split difference increased, it was necessary to consider more factors such as traffic volume when choosing an appropriate transition algorithm.