Reliability‐Based Design of Intergreen Interval at Traffic Signals

Abstract

The current method of computing the intergreen (yellow plus all‐red) interval at signalized intersections assumes that the component variables are deterministic. This paper presents a probabilistic method in which the approach speed, reaction time, deceleration rate, and vehicle length are random variables. The intergreen interval is estimated so that the dilemma zone occurs with a specified probability. A safety margin is defined as the difference between the clearing and stopping distances, which are random variables. Relationships for the mean and standard deviation of the safety margin are developed based on the first‐order second‐moment analysis. A closed‐form solution of the intergreen interval is then derived. The safety margin is assumed to be normal, and this assumption is confirmed. The probabilistic method should be valuable in designing the intergreen interval for any desired reliability level.