Reserve capacity for a road network under optimized fixed time traffic signal control

In this article, a two-stage approach to the calculation of reserve capacity for a network is presented. The first stage uses a genetic algorithm to find signal timings that optimize network performance taking traffic reassignment into account. The genetic optimizer, referred to as Genetic Algorithm Transyt Path Flow Estimator (GATRANSPFE), combines the Traffic Network Study Tool (TRANSYT) model, used to estimate performance, with the Path Flow Estimator (PFE) logit assignment tool, used to predict traffic reassignment. In the second stage, the largest common multiplier that can be applied to the Origin-Destination (OD) matrix given the optimized signal timings of stage one is found, again taking reassignment into account. This study deals with the spare capacity available to accommodate the inevitable day-to-day fluctuations in demand. The application of the two-stage procedure is illustrated for a small network with two-signal controlled junctions taken from the literature.