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Minimizing Signal Transition Impact at Intersections Caused by Pedestrian Crossings
AuthorMora Campos, Ericka Maria
Civil and Environmental Engineering
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The objective of a signal timing plan is to provide enough green time according to the traffic demands on each approach of the intersection, which includes motorized and non-motorized transportation modes. Pedestrian timing is crucial in the design since this time depends on the length of the crosswalk and typical walking speed of pedestrians, meaning that the minimum pedestrian crossing time is a predetermined value. There are two scenarios when handling pedestrian timing in a timing plan development process: accommodated or not accommodated. Accommodated pedestrian timing implies that the corresponding phase green is equal to or greater than the WALK and Flashing-Don’t-Walk (FDW) intervals of the pedestrian phase. Because pedestrians crossing a major street generally require a longer time, it is not always efficient to accommodate pedestrian timing if the side street vehicular traffic demand is low. However, if pedestrian timing is not accommodated, the signal will go into transition whenever there is a pedestrian call. The major consequence of a signal transition is disruption to signal coordination. The primary objective of this research is to analyze the impact of signal transition on intersection operations and provide recommendations on how to minimize the impact of this transition process. A good signal coordination timing plan should produce the least traffic delay and number of stops through a corridor. When a transition occurs, signal coordination is disrupted, causing an increased number of stops and traffic delays. This research particularly focused on cases where pedestrian time cannot be accommodated due to constraints on further reducing the main street green times. Signal controllers by various manufacturers have implemented different transition methods to minimize the transition impact. The focus of this research was on two transition methods within the 900 ATC Series controller by Cubic/Trafficware: Shortway (from 0 to 24%) and Longway (from 0 to 50%). The research question is which method is better depending on the circumstances of each intersection in a corridor? To answer this question, traffic volumes, cycle length, phasing sequence, and other factors must be analyzed along with their impact on transition time and intersection performance. The intersection in Reno at Oddie Boulevard and Silverada Boulevard was used as a case of study in the research. Virtual controller and hardware-in-the-loop simulation were used for conducting the analysis. The results suggested that the Shortway (Subtract) method had shown shorter transition times compared to the Longway method. Phase sequence had also shown an impact on the transition time, i.e., a shorter transition time occurred when lagging the pedestrian phase. The Longway method resulted in a fewer number of stops than Shortway when the intersection was saturated. Longway also showed to be more effective when there were a high number of pedestrian calls.