Examining the Operational Benefits of Freeway Ramp Metering Control Using CORSIM (CORridor SIMulator)

Abstract

A series of ramps could be metered to avoid flow breakdowns or to lessen the extent of congestion at freeway downstream bottleneck locations. Although ramp metering might improve the traffic flow on the freeway, it may increase the delays of vehicles behind metered ramps and induces ramp vehicles to divert if alternative routes can be found. The benefits to the overall system from metering ramps depends on factors including freeway demand flow rate immediately upstream of the metered ramps, demand flow rates at metered ramps, ramp storage length and metering rate, freeway bottleneck section capacity (both normal and breakdown conditions) and traffic diverting rate around the bottleneck. The focus of this paper is to examine how the above factors affect the operational benefits of metering ramps. In a simple transport network, various cases are designed and simulated using the CORSIM micro-simulation model, while ramp-metering benefits are investigated. It is found that benefits from ramp metering control can be achieved the most if stable operations can be maintained on both freeway and diverting route. Benefits also depend on the demand flow rate that passes through the bottleneck sections under ramp metering control condition and this study suggests that the selection of metering rate to minimize the probability of flow breakdown is important in achieving maximum benefits. It is also found that ramp metering may not be beneficial if diverting route operates poorly and congestion is likely to propagate onto the freeway.