Impact of Extended Red Clearance Intervals on Left-Turn Red-Light Violations: A Time Series Analysis

Abstract

Red-light running (RLR) incidents at signalized intersections contribute substantially to intersection-related crashes. They are increasing in number, posing a significant safety challenge. This study examines the impact of signal timing parameters, specifically red clearance intervals, on left-turn RLR violations and assesses effective countermeasures. Adjustments to red clearance and yellow intervals, in line with the ITE 2020 guidelines, were made at signalized intersections in major urban areas within the City of Phoenix. The measurements for left-turn widths at the selected study sites ranged from 60 to 125 ft, with ITE calculations resulting in red clearance intervals between 3 and 5 s. Smart sensors were deployed to collect comprehensive data on signal timings, traffic counts, and RLR violations before and after implementing the updated intervals. Analysis of the pre-and post-intervention data revealed a striking 112% increase in the frequency of RLR violations for left-turn movements following the extension of red clearance intervals. Additionally, the synergistic impact of red clearance and yellow intervals showed that the negative impact of the increased red clearance intervals had offset the positive effect of the extended yellow interval. Further analysis using the interrupted time series method confirmed a significant rise in RLR violations associated with extended red clearance intervals. These findings suggest that increasing the duration of red clearance intervals significantly increases the frequency of RLR violations for left-turn movements. While the study is focused on the City of Phoenix, its implications are relevant to urban areas with similar traffic characteristics. This underscores the importance of thoughtful consideration when modifying signal timings to address RLR behavior effectively.