Optimal ramp metering and variable speed signs for multiclass freeway traffic

The objective of the present paper is that of defining a modelling and control framework for freeway traffic in which several vehicle classes are explicitly taken into account. To this end, a multiclass model representing the dynamic behaviour of traffic in a freeway stretch is proposed. In such a model, based on a classical macroscopic model, vehicles are divided into two broad categories relevant to slow and fast vehicles. In order to evaluate the interference caused by one vehicle class on the other one, a new definition of the steady-state relation between speed and density is derived. The multiclass model is then used in a Model Predictive Control (or Receding Horizon Control) Scheme, in which traffic is controlled by regulating the vehicle access to the freeway and by limiting the vehicle speed by means of variable message signs. The presence of two vehicle classes in the overall traffic flow makes it necessary to realize dedicated control actions for each vehicle class. This means that, in the overall control scheme, the two types of control actions (ramp metering and variable speed limits) have to be determined for each vehicle class.