National Center for Sustainable Transportation

Freeway and arterial transportation networks in most districts are managed separately without any coordination. This lack of coordination increases the severity of traffic congestion when one or both systems reach their capacities. Some field studies have observed reductions in travel time by coordinating freeway ramps with adjacent arterial signals. To advance the investigation, we propose an integrated traffic management strategy that involves variable speed limit, lane change, ramp metering for freeway traffic flow control, and a traffic-responsive signal control scheme for adjacent traffic light intersections.The variable speed limit and lane change control are designed to alleviate congestion at a lane-drop bottleneck in an arbitrary section, and reject potential uncertainties from measurements or model parameters. The ramp metering algorithm takes advantage of the signal plan of neighboring arterial intersection when estimating on-ramp demands. The signal plan for each arterial intersection is determined by a simulation-based cycle length model and estimated demands of all directions, part ofwhich depend on off-ramp flow measurements. The above data sharing mechanism strengthens the connection between thefreeway and arterial networks and enhances the control performance. We demonstrate the effectiveness and quantify the benefits provided by the proposed system in terms of traffic mobility, safety and emission using microscopic traffic simulations.

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