Route diversion control in motorway networks via nonlinear optimization

The online application of nonlinear optimization methods to feedback control of motorway networks is presented. The considered control measure is route diversion via variable message signs (VMS). The control task is formulated as a dynamic, nonlinear, discrete-time optimal control problem with constrained control variables and is solved by a gradient based search. An algorithm for the heuristic search of optimal discrete (binary) control sequences is also presented. Feedback control is realized by solving the optimization problem for each control interval over a sufficiently long future time horizon (certainty equivalent open-loop feedback control). As a prerequisite, a state-space description of the network traffic dynamics is derived from a macroscopic model that is also used in the simulation program METANET. Simulation results for route diversion on a hypothetical example network are provided. The required computational effort is assessed and the control benefits are evaluated in terms of global network performance, switching frequency of VMS and user optimality