Application of PSO algorithm to coordinated ramp control

A multilayer control structure and PSO (Particle Swarm Optimization) algorithm are used for coordinated ramp control on freeways. The macroscopic model to describe the evolution of freeway traffic flow is built and the PSO algorithm is formulated. The control system is vertically decomposed into three layers: The adaptation layer to specify the values of disturbances and to adjust the parameters of traffic models, the coordination layer to determine the desired traffic density in each freeway section according to the current traffic state, and the direct control layer to keep the actual values of the traffic density in the vicinity of the nominal trajectories via PI control. PSO algorithm is used to find the optimal PI parameters of the direct control layer. Simulation results show that the control system is of good performance. It can eliminate traffic jams, maintain traffic flow stability, and make vehicles travel more efficiently and safely.