Assessing impacts of traffic signal countdown timers on safety and efficiency at signalized intersections

Traffic Signal Countdown Timer (TSCT) displays the remaining times of green, yellow, and red intervals at a traffic signal. While TSCT has widely been implemented in various countries, there is a lack of studies that comprehensively assess the effects of TSCT on traffic safety and efficiency using a simulation based on understanding of changes in driver behavior in different signal phases in the presence of TSCT.

This study investigates the impacts of TSCT on traffic safety and efficiency at signalized intersections with high truck volume along the Huron Church Road in Windsor, Ontario, Canada. Driver behavior and traffic flow were simulated using PTV Vissim for the four scenarios - no-timer, Green Signal Countdown Timer (GSCT), Red Signal Countdown Timer (RSCT), and a combination of GSCT and RSCT (GSCT + RSCT). Based on the observational data from previous field studies, changes in driver behaviors in the presence of TSCT were replicated by dynamically adjusting the simulation parameters in different signal phases using Vissim-COM interface.

The Crash Potential Index (CPI) decreased by 37% while the speed of the road network increased by 6% in the GSCT + RSCT scenario compared to the no-timer scenario. The RSCT reduced the CPI more than the GSCT but did not significantly improve the traffic efficiency. The increase in speed near the intersection during the green phase was observed in the GSCT scenario, whereas smoother deceleration rate of approach vehicles during the red phase was observed in the RSCT scenario. Due to these changes, the average number of vehicles entering the intersection during the green phase in each cycle increased in the GSCT + RSCT scenario. Moreover, the TSCT helped cars avoid rear-end conflicts and increased truck speed.

Both GSCT and RSCT can be implemented to improve traffic safety and efficiency at signalized intersections.