Ramp metering control for two vehicle classes to reduce traffic emissions in freeway systems

In the paper a two-class ramp metering control strategy is proposed in order to minimize the traffic emissions in a freeway system. Two vehicle categories, i.e. cars and trucks, are explicitly represented in the dynamic model and separate control actions are devised for the two classes. The traffic emissions of vehicles are represented according to an average-speed model, assuming that the emission factor for a given pollutant depends only on the average speed during a trip. The considered control strategy is PI-ALINEA, suitably adapted to the two-class case, in which the occupancy set-point is set in order to reduce both the traffic emissions and the congestion level. The simulation tests have been realized in order to evaluate, for the one-class and for the two-class cases, how the total emissions and the total time spent by vehicles in the freeway system vary depending on the occupancy set-point, in different traffic scenarios.