Probabilistic Evaluation of Traffic Randomness Effects on Intergreen Time Design Based on a Safety Reliability Model

Conventional methods of intergreen time design are based on deterministic traffic flow theory and are thus difficult to fully account for traffic randomness especially driver’s decision error. The objective of this paper is to develop a probabilistic method to extensively investigate the effects of traffic flow randomness and driver’s decision error on the determination of intergreen times. An analysis framework was firstly proposed based on a safety reliability model earlier developed by the authors. A comprehensive sensitivity analysis was then performed to look into the fluctuation of safety reliability towards critical input variables as well as its variations and correlations. Based on the sensitivity analysis results, two logistic regression models were then developed to quantify the effects of each random component on the probability of risky behavior and the probability of clearance failure respectively, which were used for evaluating the safety reliability during the intergreen intervals in the adopted model. To facilitate easy applications of the proposed approach, a set of scenario analysis covering typical conditions were followed to calculate the required durations of intergreen intervals under different safety reliability levels. Application tables correspondent to those typical conditions were finally provided for design purpose, which are able to recommend more sophisticated intergreen times based on given safety reliability levels, and thus aid the practitioners to select proper intergreen times according to local conditions without any complicated calculation.