Safety Evaluation for Intergreen Intervals at Signalized Intersections Based on Probabilistic Method

This study presents a probabilistic safety estimation approach based on traffic conflict technique. The study aims to investigate the impacts of the German signal control policy and intergreen design method on safety during intergreen intervals at signalized intersections in Japan. To facilitate application of the policy, the uncertainty of input variables and of safety itself, indicated by the postencroachment time, was analyzed first by means of field data collected at 12 typical intersections in Japan and Germany. A few case studies were then examined with Monte Carlo simulation. The results indicated that safety during the intergreen interval and its reliability might significantly drop if inter-green times were simply changed from the values based on the Japanese method to the values based on the German method without supplementary countermeasures. However, safety as well as reliability can be maintained if the Japanese control policy is completely replaced with the German one.