Evaluating the Effects of Countdown Timers on Intersection Safety: A Case Study in Arak, Iran

Roadway Intersections are known as safety bottlenecks in urban traffic networks. According to the national traffic accident fatality statistics of Iran, 27% of all fatal accidents happened in urban areas in 2017. This rate is as low as 8% for provinces with very low population density and as high as 74% for the Tehran province, which is the most populated province of the country. Many measures have been taken to increase intersection safety. But lately, it has been illustrated that some of them may even reduce safety in some case. Countdown devices as one of these measures have been evaluated in this study. Aside with increasing intersection efficiency, one other purpose of using Green Signal Countdown Devices (GSCD) and Red Signal Countdown Devices (RSCD) is to increase intersection safety by giving drivers information about the remaining time of each signal phase. four scenarios were designed and separately implemented at one intersection of Arak urban network, Iran. Data was collected by reviewing videos recorded by a traffic control camera located at the intersection and totally 1888 cycles have been investigated. This study demonstrated that it is necessary to evaluate each countdown timer when operating alone, as well as in combination state. A Ttest analysis has been applied and the results show that GSCD has a positive effect on intersection safety indicators, most effectively when RSCD is disabled. Statistical analyses indicate that the “best scenario” caused enhancement of total safety indicators compared to the average of other three scenarios for about 10%.