STOCHASTIC TRAFFIC SIGNAL TIMING OPTIMIZATION

Signalized intersections are a critical element of an urban road transportation system and maintaining these control systems at their optimal performance for different demand conditions has been the primary concern of the traffic engineers. Currently, the average control delay is used as a performance measure of a signalized intersection. The control delay is estimated using the delay equation provided by the Highway Capacity Manual (HCM). The HCM delay equation is a function of multiple input parameters arising from geometry, traffic and signal conditions. Variables like volume, green time and saturation flow rate that influence delay computations are stochastic variables, which follow their characteristic distribution. This implies that delay has to be estimated as a distribution as against the point estimate, the average delay. Various simulation programs and optimization techniques have evolved that aid the traffic engineer in the optimization process. None of the optimization programs consider the day-to-day stochastic variability in the delay during the optimization process. The purpose of this research is to estimate variability in delay at signalized intersections and incorporate the variability in the optimization process. An analytical methodology to compute the variance of delay for an isolated intersection and arterial intersections is developed. First, delay variance is computed for an isolated intersection using expectation function method for undersaturated conditions and integration method for oversaturated conditions. The variance computation for an isolated intersection is expanded to arterial intersections using the integration method and the analytically approximated platoon dispersion model. The delay variance estimates are then utilized in the optimization of intersections. A genetic algorithm approach is used in the optimization process using either average delay or the 95th percentile delay as an objective function. The results of the optimization, especially for isolated intersections, have shown considerable improvement over SYNCHRO, a signal optimization program, when evaluated using microscopic simulation programs SIMTRAFFIC and CORSIM. However, the results of arterial optimization did not show any significant improvement over the SYNCHRO.