Efficiency Assessment of Extended Change and Clearance Intervals on Signalized Intersections and Corridors

Alfawzan, Mohammed S.; Radwan, Essam; Elbany, Marwa; Almoshaogeh, Meshal; Dahish, Hany A. · 2025 · Crossref

DOI: 10.18280/ijtdi.090211

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Summary

This study evaluates the operational and safety impacts of extending change and clearance intervals at signalized intersections, motivated by the Florida Department of Transportation’s (FDOT) initiative to reduce red-light running and mitigate "dilemma zones." The dilemma zone is defined as the area where drivers face uncertainty about whether to stop or proceed during a yellow signal. The research specifically assesses how FDOT’s signal retiming efforts, which lengthen these intervals, affect intersection performance and corridor efficiency in Central Florida. The methodology involved a comparative analysis of three signal timing patterns across twenty signalized intersections along three major corridors (SR 50, SR 535, and SR 536). Pattern 1 represented the baseline timing with a 1-second perception-reaction time (PRT). Pattern 2 reflected the current FDOT implementation, increasing the PRT to 1.4 seconds and adjusting clearance intervals. Pattern 3 was a proposed alternative utilizing a 2.0-second PRT. Data collection included field observations of traffic volumes, queue lengths, and signal timing during peak hours. The study employed microsimulation analysis using the SimTraffic component of Synchro 8 software. The model was calibrated using field data to minimize the mean absolute percentage error between simulated and observed metrics. Key performance indicators measured included intersection delay, volume-to-capacity (V/C) ratios, and 95th percentile queue lengths for critical left-turn movements. The results indicate that extending change and clearance intervals significantly degraded operational performance. Both Pattern 2 (FDOT implementation) and Pattern 3 (proposed alternative) led to substantial increases in intersection delay and V/C ratios compared to the baseline Pattern 1. The increase in delay was more pronounced when moving from Pattern 1 to Patterns 2 and 3, while the difference between Patterns 2 and 3 was marginal. Furthermore, these extended intervals caused noticeable increases in overall travel time and delay along the studied corridors. The study found that while longer intervals were intended to enhance safety by reducing red-light running, they resulted in inefficient traffic flow, with some intersections experiencing higher delays due to the additional time allocated to non-green phases. The significance of this research lies in highlighting the trade-offs between safety and operational efficiency in signal timing design. The findings suggest that while extending change and clearance intervals may address dilemma zones and reduce red-light violations, it comes at the cost of increased congestion and delay. This provides critical evidence for traffic engineers and policymakers, indicating that static extensions of timing intervals may not be optimal for all contexts. The study underscores the need for balanced approaches that consider both safety metrics and operational performance, potentially favoring adaptive or context-aware timing strategies over uniform static increases in interval durations.

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