Optimizing Coordinated Ramp Metering: A Preemptive Hierarchical Control Approach: Fid-Bau Portal

Optimizing Coordinated Ramp Metering: A Preemptive Hierarchical Control Approach

Zhang, Guohui / Wang, Yinhai

Abstract: This article describes a coordinated ramp metering algorithm for systematically mitigating freeway congestion. A preemptive hierarchical control scheme with a three‐priority‐layer structure is employed in this algorithm. Ramp metering is formulated as a multiobjective optimization problem to enhance system performance. These optimization objectives include promptly tackling freeway congestion, sufficiently utilizing on‐ramp storage capacities, and preventing on‐ramp vehicles from overflowing to local streets, balancing on‐ramp vehicle equity, and maximizing traffic throughputs for the entire system. Instead of relying heavily on accurate estimates of freeway traffic flow evolvement, this new approach models ramp meter control as a linear program and uses real‐time traffic sensor measurements for minimizing the indeterminate impacts from the mainstream flow capacities. VISSIM‐based simulation experiments are performed to examine its practicality and effectiveness using geometric and traffic demand data from one real‐world freeway segment. The simulation test results show that the proposed ramp metering approach performed well in optimizing overall freeway system operations under various traffic conditions. The system‐wide optimal control performance can be achieved to quickly mitigate freeway congestion, prevent traffic from overflowing to local streets, and maximize overall traffic throughputs. The proposed ramp metering approach can dynamically assemble relevant ramp meters to work together and effectively coordinate the individual meter rates to leverage their response strengths for minimizing time to clear the congestion. This study demonstrates that utilization of existing freeway infrastructure can be optimized through the proposed algorithm.