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Open Access Publications from the University of California

Freeway Traffic Control Using Variable Speed Limits


The work reported here includes the development of the underlying theory for detecting traffic flow breakdown at a bottleneck and for defining the speed profiles that vehicles should be following in order to maximize the flow through the bottleneck region. It also includes a preliminary test of the communication of the variable speed limit values to an instrumented vehicle for display to drivers from the general public, in order to determine their reactions to the variable speed limits. The selection of variable speed limits (VSL) to reduce traffic breakdowns is based on careful modeling of the traffic dynamics and estimation of the probability of breakdown as a function of traffic speed and density. The VSL values chosen by the algorithm developed here were broadcast to a test vehicle driven along the I-80 corridor by 16 drivers from the general public, and their reactions to the VSL information were captured by recording data about their driving behavior and collecting their responses to a questionnaire. These results indicated that although the VSL concept is very promising, the implementation needs to provide for better filtering of noisy and inconsistent data so that drivers receive a display of VSL values that are stable in location and time and appear believable to the drivers.

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