Optimize the Settings of Variable Speed Limit System to Improve the Performance of Freeway Traffic

This paper investigates variable speed limit (VSL) systems, trying to optimize the system designs when the variable message signs (VMSs) are movable. The optimization problem is formulated as a large mixed-integer nonlinear programming problem, whose decision variables include the number of VMSs to be deployed, the locations of the VMSs, and the speed limits posted on the VMSs. Two objectives are considered, one is to smooth the flow propagation, and the other is to minimize the environmental impact of freeway traffic. Moreover, a genetic algorithm is proposed to solve the complex problem. Numerical examples performed on a real freeway segment show that VSL can effectively achieve smooth flow and reduce the environmental impact of freeway traffic.