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https://nap.nationalacademies.org/catalog/27432/critical-issues-in-transportation-for-2024-and-beyond

Preparations for Field Testing of Combined Variable Speed Limit and Coordinated Ramp Metering for Freeway Traffic Control

The proposed effort will conduct a limited scale field test of a freeway traffic control strategy combining Variable Speed Limits (VSL) and Coordinated Ramp Metering (CRM) to determine its ability to increase the effective capacity of a recurrent bottleneck. This addresses an urgent problem for California's congested urban freeways, offering a potentially inexpensive way of increasing the achievable capacity of the recurrent bottlenecks that limit traffic flow and speed during busy periods. If successful, it can be deployed in congested freeway corridors throughout the state. The proposed effort will prepare the way for future field testing of Variable Speed Advisory (VSA) and Coordinated Ramp Metering (CRM). The work will include: (1) Refinement of site selection criteria and selection of proper site for field testing; (2) Extensive literature review focusing on the experiences of field testing and practice of VSL/VSA and CRM in the U.S., Europe and world-wide; (3) Preparations for process control computers and single functionality Variable Message Signs (VMS) that will be needed for the subsequent tests; (4) Data collection and microscopic traffic modeling of selected site; and (5) Validation of the previously developed VSL and CRM simulation and algorithm for the selected site. The VSA and CRM strategies are expected to relieve congestion by avoiding or delaying traffic flow breakdowns at recurrent freeway bottleneck locations, based on results of prior research. The new research and testing are needed to determine how well the previous theoretical results and the actual experiences with these strategies in other countries can be extended to real-world operations in California. The deployable outcome of the project will be the detailed plans for field testing of VSA and CRM on a California freeway corridor, developed in close coordination with the local Caltrans District traffic operations personnel. This will provide the basis for a subsequent field test, and assuming success of the field test the strategies could then be deployed by Caltrans. Constraints: The project needs cooperation with the local District traffic operations staff, but interest has already been expressed by both District 4 and 7.