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

A series of ramps could be metered to avoid flow breakdown or to lessen the extent of congestion at freeway downstream bottleneck locations. Although ramp metering might improve the traffic flow on the freeway but it increases the delays to 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 depend on factors including freeway demand flow rate immediately upstream of 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 above factors affect the operational benefits of metering ramps. In a simple transport network, various cases are designed and simulated using 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 suggest that 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 likely to propagates onto freeway.