Design of intergreen times based on safety reliability

This study proposes a stochastic approach for the design of intergreen times, that is, signal change and clearance intervals, at signalized intersections based on safety reliability. Unlike the conventional deterministic methods, the proposed method accounts for the uncertainty of input variables deriving intergreen times as well as driver decision randomness at the onset of yellow. The probability of risky behavior, including abrupt stop and red light running, was selected as the safety reliability measure for determining yellow time, and the probability of the occurrence of clearance failure was used as the measure for determining all-red time. A theoretical model of estimating safety reliability and deriving intergreen times was developed and was validated by the use of the Monte Carlo simulation technique. Comparisons with the current methods used in Japan, the United States, and Germany indicated that the proposed method captured the probabilistic nature of traffic and driving decision and thus provided a more rational design of intergreen times.