Time series analysis of resampled red-light violations to understand drivers' adaptation to extended yellow intervals.

INTRODUCTION: Red-light running (RLR) poses significant safety risks at signalized intersections, often leading to severe crashes. Increasing yellow intervals has been proposed as a countermeasure for RLR violations. Despite the immediate effectiveness of increasing yellow intervals in reducing RLR violations, concerns remain regarding potential driver adaptation over time. This study aimed to evaluate the long-term effectiveness of increased yellow intervals on driver compliance using RLR events on through and left-turn movements.

METHOD: The data were collected from three intersections in the Phoenix metropolitan area for 81 and 496 days (about one and a half years) before and after increasing the through and left-turn yellow intervals. An Interrupted Time Series Analysis (ITSA) and Block Bootstrap Resampling were applied to determine the significance of the intervention and the impact of the intervention through time.

RESULTS: The results showed that increasing the yellow intervals led to a significant and sustained reduction in RLR violations for both through and left-turn movements across all treatment sites. Importantly, ITSA results indicated no evidence of driver adaptation, reinforcing the long-term effectiveness of increasing yellow intervals on RLR. This research also shows the impact of movement types and site-specific characteristics, including traffic volume and intersection layout, on the effectiveness of signal timing adjustments for safety improvements.

PRACTICAL APPLICATIONS: Understanding the drivers' adaptation to the changes in signal timing could assist agencies when considering using longer yellow intervals to address chronic red light running violations and defining the allowable period before readjustment of signal timing plans for safety purposes.