Investigation on the Effects of Countdown Timers on Safety and Performance of Traffic at Signal Controlled Intersections

This article reflects the findings of a study on the impacts of countdown timers on safety and performance of traffic at signal controlled intersections. Parameters such as late-stopping ratio, early start ratio, number of red light violations and number of accidents were examined to consider safety impacts of these timers. Additionally, saturation flow rate, saturation headway and start-up delay parameters examined to compare capacity and traffic performance at 6 signalized intersections located in the Yazd and Sirjan cities where the countdown timers where left on and then switched off. Data required for this purpose was provided from the video recordings of video surveillance cameras. Comparison between the timer on and off situations indicated that the number of red light violations reduced by about 1.16%, when the timer was on, the number of accidents showed no clear variation and early start ratio increased by about 1.7% when the timer was on. However, Mann-Whitney test based on a 95% Confidence interval showed that there was no significant difference between these two situations. Late-stopping ratio on average reduced by about 2.34% when the timer was on and Mann-Whitney test results showed that there was a significant difference between the two situations. . Investigation on start-up delay parameter indicated that there was a significant difference between the two situations. In this regard, start-up delay of all the intersections increased by about 22.8% when the timers were off. The t test for analyzing saturation headway and saturation flow rates indicated that there was no significant difference between the two situations.