PI: Yao-Jan Wu, Ph.D., P.E.
Co-PI: Tom Cooper
Sponsor: City of Phoenix
Oct. 2023 - May 2026
This project represents the third phase of an ongoing research effort conducted in partnership with the City of Phoenix Street Transportation Department to evaluate the effects of traffic signal timing modifications on driver compliance behavior and red-light running (RLR) violations at signalized intersections. Building on the findings of the previous two phases, Phase 3 expanded the evaluation to fifteen additional signalized intersections within the City of Phoenix, each equipped with NoTraffic© intelligent traffic detection sensors, over a sixteen-month data collection period. The study was conducted in two parts. Part 1 aimed to evaluate the effects of modifying yellow change intervals on driver compliance behavior and RLR violations, comparing interval calculations based on two guidelines: the ITE 2020 Guidelines for Determining Traffic Signal Change and Clearance Intervals and the NCHRP Report 731 Guidelines for Timing Yellow and All-Red Intervals at Signalized Intersections. This comparison was particularly focused on left-turn movements, where the two guidelines differ in both the kinematic equation applied and the assumed approach speed, resulting in different interval values. Part 2 aimed to evaluate the effects of modifying red clearance intervals based on the ITE 2020 guidelines on driver compliance behavior and RLR violations, both independently and in conjunction with the longer yellow change intervals implemented during Part 1. The study utilized a rigorous before-and-after experimental design incorporating control and treatment sites across multiple study periods to enable statistically reliable evaluation of the implemented signal timing modifications.