Comparison of local feedback controllers for the mainstream traffic flow on freeways using variable speed limits

Two simple controllers for local feedback mainstream traffic flow control (MTFC) on freeways, enabled via Variable Speed Limits (VSL), are proposed. Both controllers are evaluated and compared to a previously developed local MTFC feedback cascade controller and to a sophisticated optimal control approach. All feedback controllers rely on readily available real-time measurements; are simple and robust; and take into account a number of practical and safety restrictions; therefore being suitable for implementations in the field. The evaluations are conducted for a hypothetical freeway network by use of a validated second-order macroscopic traffic flow model. The results show that the feedback controllers exhibit a satisfactory control behavior and, indeed, approach the optimal control results. Recommendations for the operation of the feedback controllers are given.