Understanding Drivers' Compliance Behavior: Data-Driven Assessment of Longer Yellow Intervals

Red-light running (RLR) behavior poses significant risks at signalized intersections and has emerged as a leading cause of intersection-related crashes. The Phoenix metropolitan area had 113 RLR-related fatalities and 9,320 injuries from 2014 to 2020. To effectively mitigate RLR violations and uphold the safety of all road users, it is crucial to investigate RLR behavior at local intersections, evaluate the impact of different signal timing parameters—such as the yellow interval—on the frequency of RLR violations, and, finally, identify effective countermeasures. This study investigated the effect of updating the yellow interval on the frequency of red-light violations. Twelve intersections within the City of Phoenix were carefully selected as study sites. Then, smart sensors were installed to collect various data types, such as signal timing parameters, the vehicle count, and RLR violation data. Based on the ITE 2020 guidelines, yellow intervals were adjusted at each intersection. The effects of increased yellow intervals on RLR violations were examined by utilizing a comprehensive experimental before-and-after design. The before-and-after study results indicated that increasing the yellow intervals significantly reduced the average frequency of RLR violations for both through and left-turn movements by 83% and 72%, respectively. The results of this research are instrumental in informing transportation agencies, enabling them to adopt evidence-based approaches to signal timing strategies that enhance intersection safety and effectively reduce RLR violations.