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

Document Type : Research Article


1 Associate Professor, School of Civil Engineering, Iran University of Science and Technology, Tehran, Iran.

2 Road Safety Research Centre, Iran University of Science and Technology, Tehran, Iran.

3 School of Civil Engineering, Iran University of Science and Technology, Tehran 13114-16846, Iran.

4 Cambridge Systematic, Inc., 25 Beaver St, Ste 201, New York NY 10004.


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 and to reduce conflicts between vehicles moving in different approaches. Countdown devices as one of these measures have been evaluated in this study. Green Signal Countdown Devices (GSCD) and Red Signal Countdown Devices (RSCD) have been used to increase intersection safety by giving drivers information about the remaining time of each signal phase, especially at the end of the green phase, to better decide between stopping or crossing the intersection. But lately, it has been illustrated that these devices may even reduce safety in some cases. To access the safety impacts of these devices, four scenarios were designed and separately implemented in one intersection of Arak urban network, Iran. Data was collected by reviewing videos recorded by a traffic control camera that was installed at the intersection. This study demonstrated that it is necessary to evaluate each countdown timer when operating alone, as well as in combination state. A T-test analysis has been applied and the results show that GSCD has a positive effect on intersection safety indexes, most effectively when RSCD is disabled.


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