RHODES-ITMS CORRIDOR CONTROL PROJECT

The RHODES-ITMS Corridor Control project addresses real-time control of ramp meters of a freeway segment, with consideration of the traffic volumes entering and leaving the freeway from/to arterials, and the regulation of these volumes via real-time setting of ramp metering rates. Current approaches to traffic responsive control of ramp meters include (a) time-of-day control, (b) locally responsive strategies and (c) area-wide linear programming based approaches (currently implemented in parts of Europe). None of these approaches are both real-time responsive to traffic conditions and consider the multiple objectives of minimizing freeway travel times and decreasing congestion/queues at the interchanges. A control system, MILOS (Multi-objective Integrated Large-scale Optimized ramp metering System), was developed that determines ramp metering rates based on observed traffic on the freeway and its interchange arterials. MILOS temporally and spatially decomposes the ramp-metering control problem into three hierarchical subproblems: (1) monitoring and detection of traffic anomalies (to schedule optimizations at the lower levels of the control hierarchy), (2) optimization to obtain area-wide coordinated metering rates, and (3) real-time regulation of metering rates to adjust for local conditions. Simulation experiments were performed to evaluate the MILOS hierarchical system against (a) "no control" (i.e., when no ramp metering is in effect), (b) a locally traffic-responsive metering policy, and (c) an area-wide LP optimization problem re-solved in 5-minute intervals. Three test scenarios were simulated (1) a short "burst" of heavy-volume flows to all ramps, (2) a three-hour commuting peak, and (3) a three-hour commuting peak with a 30-minute incident occurring somewhere in the middle of the corridor. The performance results indicate that MILOS is able to reduce freeway travel time, increase freeway average speed, and improve recovery performance of the system when flow conditions become congested due to an incident.