PI: Yao-Jan Wu, Ph.D., P.E.
Co-PI: Tom Cooper
Sponsor: City of Phoenix
May 2022 - May 2026
The Center for Applied Transportation Sciences (CATS) has partnered with the City of Phoenix Street Transportation Department since May 2022 to investigate road users' compliance with yellow and red clearance time intervals at signalized intersections and to inform signal timing design.
Through this multi-phase effort, the research team examined whether implementing updated ITE 2020 yellow and red clearance intervals could help reduce red-light-running (RLR) violations. In the first two phases, the team developed a before-and-after experimental design across 12 signalized intersections in the City of Phoenix, focusing on the relationship between interval changes and RLR frequency, including left-turn phase violations. The success of these early phases led to the continuation and expansion of the partnership through Phase 3, reflecting the City's continued confidence in CATS as a trusted technical partner.
Phase 3 expanded the evaluation to fifteen additional signalized intersections equipped with NoTraffic intelligent traffic detection sensors, over a sixteen-month data collection period. The study was conducted in two parts, comparing yellow change interval calculations based on the ITE 2020 Guidelines and the NCHRP Report 731 Guidelines, and evaluating red clearance interval modifications both independently and in conjunction with the updated yellow change intervals.
Through this multi-phase effort, CATS works closely with City staff to develop practical, data-driven solutions that enhance intersection safety and support Phoenix's long-term traffic signal design goals.