An Indicator for Determining the Control Timing of Ramp Metering on Urban Freeway Corridors

Abstract

Existing ramp metering strategies mainly focus either on local control applications or on the coordination of ramp metering along the corridor. There appears a lack of effective indicators for identifying the control timing and evaluating the effects of ramp metering. Macroscopic Fundamental Diagram (MFD), describing the relationship between productions and vehicle accumulations in a traffic network, is useful in representing the traffic states of a traffic network. Traffic breakdown is a stochastic phenomenon and can be used for analyzing the instability of traffic flows. This paper proposes a novel performance indicator, namely the traffic performance index (TPI), for determining the control timing of ramp metering on urban freeway corridors based on the MFD and traffic breakdowns. It is found that the determination of the control timing of ramp metering on urban freeway corridors should consider the tradeoff between the network accumulations and the stability of traffic flows. It also shows that there exists a critical value of TPI, at which the network production is high and the traffic flows are relatively stable.