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This paper demonstrates the use of a discrete event traffic micro-simulation model to study the safety impacts of the introduction of an incident reduction (IR) function into a vehicle-actuated traffic signal controller. The IR function is based on that used in signal controllers in Sweden. The IR function is designed to reduce the number of stop-or-go decisions by drivers when caught in the dilemma zone at the onset of the amber signal. A correctly adapted IR function was found to greatly enhance the safety performance of signalized intersections. The simulation experiment described in the paper is based on empirical data from a suburban vehicle-actuated signalized intersection. It was conducted specifically to investigate the effects of the standard IR function on three proximal safety indicators: time to collision, red light violations, and required braking rates. The simulation results demonstrate a significant improvement in the time to collision (22%), red light violations (6%), and required braking rate when the IR function was in operation and a small positive influence on traffic movement through the intersection. Importantly, this study has illustrated the potential for using traffic microsimulation modeling for traffic safety evaluation.

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Safety in the traffic system is often measured by the number and severity of traffic crashes. This long-standing approach has established the use of crash data as an accepted measure of the lack of safety. There is, however, a distinct need for faster, more informative, and more resource-effective methods that yield valid and reliable safety measures and a foundation for predictive modelling. This paper is primarily concerned with traffic safety assessment and prediction based on proximal safety indicators and associated measurement techniques. It reviews the concepts and methods related to three different proximal safety indicators: time-to-accident, time-to-collision and post-encroachment-time. It shows how they can be measured using field data. Similar measures can also be obtained from simulation modelling. The use of simulation models for measuring and predicting intersection safety offers considerable potential for proactive safety analysis.