Variance of Vehicle Change Intervals

Abstract

A statistical analysis is presented of the length in time of the vehicle change interval, i.e., the sum of the yellow and all red times, for an approach to a signalized intersection. The analysis is based on a widely utilized equation for computing the required length of time of the vehicle change interval. Vehicle speed on the approach to the intersection is found, surprisingly, to make a negligible contribution to the variance of this time, while vehicle deceleration is found to be very important. The results of the statistical analysis reveal that the application of the standard equation for the length of the vehicle change interval by the traffic engineer is misleading in terms of the traffic situation it truly represents.