Optimization of traffic flows in congested metropolitan areas

A control methodology, whose objective is the optimal distribution of vehicle flows to alternate paths when the main path to reach a certain destination is congested, is proposed in this paper. The control is actuated by means of variable message signs (VMSs) which are located in some (suburban) links of the traffic network. The displayed messages (control variables) "induce" drivers to follow alternate paths, with the consequence of decongesting links in the main path. The optimization of traffic flows is accomplished over a network model which explicitly considers queues in the links, in order to take into account congestion phenomena which usually characterize urban traffic networks (spillbacks, bottlenecks, etc.). The optimization problem, which is described in the paper, is constrained by the discrete-time state equations of the network model, which provide the dynamics of the number of vehicles (both running and queued) in the links.