Reliability Analysis of Minimum Pedestrian Green Interval for Traffic Signals

The current method of computing the minimum pedestrian green interval for intersection signal timing assumes that the component variables are deterministic. This paper presents a probabilistic method in which the pedestrian start-up time and walking speed are random variables. To establish pedestrian characteristics, data were collected at 14 intersections in downtown, suburban, and tourist areas. The method is based on a safety margin that is defined as the difference between the supplied and demanded green intervals, where the demanded green interval is a random variable. Relationships for the mean and standard deviation of the safety margin of the demanded green interval are developed on the basis of the first-order second-moment analysis. A closed-form solution for the minimum supplied green interval is then derived as a function of the relevant variables, including the vehicular intergreen interval and its component variables. A procedure for establishing the walk and the flashing "don't walk" intervals is presented. Graphical aids for determining the minimum pedestrian green interval were developed, and application of the proposed method is illustrated using numerical examples. The sensitivity analysis shows that the minimum pedestrian green interval is much more sensitive to the walking speed than the start-up time or their correlation. (C) 2013 American Society of Civil Engineers.