Real-Time Crash Risk Reduction on Freeways Using Coordinated and Uncoordinated Ramp Metering Approaches

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This study was conducted to examine the ability of two ramp metering strategies at reducing the real-time crash risk along a typical urban freeway. The strategies were tested using a simulated freeway network of Interstate-4 in Orlando, Fla. created in PARAMICS microsimulation. Measurements of the crash risk along the freeway were estimated using models created by the first writer which calculate rear-end and lane-change risks along the freeway using offline geometric characteristics and real-time loop detector data. The ramp metering strategies tested were the uncoordinated ALINEA algorithm and the coordinated Zone ramp metering algorithm. Additionally, two implementation methods of these algorithms were examined: the traffic-cycle realization which allows vehicles to enter the network in platoons and the one-car-per-cycle (OCPC) realization which allows a single vehicle to enter the freeway per traffic cycle. This study shows that the ALINEA and Zone algorithms both successfully reduce the real-time cra...