Evaluating traffic safety and performance effects of countdown timers on signalized intersections: a driving simulator study

During the last few years application of numerical countdown timers on traffic lights has become more popular. However, there are only a handful of scientific studies that explored the performance of such system. These studies often report contradicting results, most probably due to different driving cultures. Within the context of this study, a comparative analysis was conducted between three different configurations, namely “without countdown timers”, “with entire phase countdown timers” and “with final-stage countdown timers”, in which both traffic safety and traffic performance aspects were analyzed. Since no countdown timers have yet been implemented in Belgium, the driving simulator approach was selected to simulate individuals’ behavior and different conditions’ implications. The sample population consisted of individuals who were in possession of a valid driver's license and that were accustomed to the Belgian driving culture. In total, 49 test subjects participated in the experiment. The simulation experiment comprised of six unique conditions, in which the different traffic light configurations were combined with a dilemma zone and a red-on-approach scenario. The results showed that the amount of stopping decisions increased when countdown timers were installed, indicating that improper early-stop ratios increased. No aggressive accelerations were measured for either one of the configurations, but the deceleration behavior showed that stopped drivers for the “entire phase countdown” already decreased their speed up to 150 meters in advance of the intersection. Furthermore, both countdown timers were able to more than halve the maximum applied braking force of the no timer conditions. With regard to the red phase scenarios, the results showed a statistical significant decrease of reaction times and start-up lost times of around 1.40 and 1.25 seconds compared to no timing conditions. No significant difference between the types of countdown timing was found.