Optimization of Coordinated Multi-Ramp Metering Control with Simultaneous Perturbation Stochastic Approximation (SPSA)

 Ramp metering has been recognized as one of viable strategies of freeway traffic management, which may improve travel speed as well as reduce delay. In this study, a dynamic model is developed to optimize metering rates of a series of on-ramps which maximize the total throughput subject to vehicle density, roadway capacity, and queue length constraints with simultaneous perturbation stochastic approximation (SPSA). A calibrated microscopic traffic simulation model is used to evaluate the performance of the developed model. Results show that the total throughput of the studied freeway can be increased without increasing the total delay after implementing optimal metering rates. The developed SPSA has demonstrated itself as an efficient algorithm to search for the optimal solution of a dynamic, multivariate, and non-linear problem. Keywords Ramp metering, traffic management, freeway, delay, optimization, simulation