Ramp Metering Enhancements for Postponing Freeway-Flow Breakdown

Ramp management is one of several functions performed to optimize traffic operations along a freeway. Existing ramp metering algorithms have been shown to be successful in increasing freeway throughput, and reduce overall travel time. Recent research has shown that there is a correlation between the number of vehicles arriving in clusters from the ramp and the probability of breakdown (i.e., beginning of congestion) at the ramp merge. The objective of this research was to develop enhancements for ramp metering strategies so that they can postpone the breakdown and reduce congestion at freeway facilities with recurring congestion. This research first developed a process for obtaining breakdown probability models for existing critical ramps. Next, it proposed specific enhancements to existing ramp metering algorithms which incorporate probability of breakdown models. Proposed enhancements are presented for two algorithms: the Minnesota Stratified Ramp Metering Algorithm (SZM), and the Ontario COMPASS algorithm. Simulation was used to replicate these algorithms and evaluate the proposed enhancements. The results of these experiments showed that the enhancements are effective in postponing congestion at the two sites evaluated by 17-35 minutes.