Sustainable ramp metering for freeway traffic control

The chapter focuses on ramp metering control strategies used to regulate traffic in freeway networks. Starting from a detailed survey of the most common scientific works devoted to the development of ramp metering control algorithms, the chapter focuses on recent approaches devoted to sustainable ramp metering. These works are mostly devoted to control freeway traffic systems not only to reduce congestion phenomena and to homogenize traffic conditions, but also to explicitly reduce traffic emissions in the system. Another important feature of modern traffic controllers is that they can be of the multi-class type, i.e., they are able to compute different control actions for different classes of vehicles, which can be cars, trucks, specific vehicles, and so on. The chapter discusses, in the final part, a sustainable ramp metering control scheme, that is a twoclass feedback controller, which could be effectively applied in real freeway systems. The reported simulation results show that this type of controller can be used not only to reduce congestion, but also to reduce traffic emissions.