Optimizing Coordinated Ramp Metering: A Preemptive Hierarchical Control Approach

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.

Capacity of Freeway Merge Areas with Different On-Ramp Traffic Flow

“…Meanwhile, the amount of time gap where a k vehicle platoon could merge onto freeway from the ramp is TP m k m . In this situation, the total volume of vehicles that can merge onto the freeway from the on-ramp could be calculated by Equation (4).…”

“…Interactions are dynamic in freeway merge areas, and so the operating conditions on the freeway can affect the operating conditions on the ramp, and vice versa [2]. Thus, understanding the behaviour of on-ramp flows and estimating the capacity of freeway merge areas are of critical importance in developing effective operational strategies for freeway management [3][4][5].…”

DynaTAM: an online algorithm for performing simultaneously optimized proactive traffic control for freeways

“…Their paper features a hierarchical structure with three layers: (1) the estimation and prediction layer; (2) the optimization layer; and (3) the direct control layer to estimate the optimal RM control plan. Zhang and Wang (2012) proposed another multi-layered control strategy to perform coordinated control with the considerations of both mitigating mainlane congestion and preventing spillback to local streets.…”

Nature Inspired Computing: An Overview and Some Future Directions

“…This optimum seeking can be formulated as an optimisation problem [ 12 – 15 ]. That is, it is reduced to finding the best solution measured by a performance index often known as objective function in many areas of computing and engineering which varies from problem to problem [ 16 – 19 ].…”