Freeway congestion occurs when the number of vehicles on the freeway exceeds its capacity, which often the case during morning and evening commute periods. One strategy to combat this problem is ramp metering. Ramp metering systems consist of traffic signals and controllers that moderate the flow of vehicles from on-ramps to the freeway mainline. Sonoma County began to activate metering systems in 2014 and expanded their use in the two to three subsequent years. This independent study evaluated the change in flow and occupancy along a US-101 corrridor through Sonoma County using freeway detector data. We found that the overall volume of traffic increased after ramp metering was implemented, and also that the freeway was able to accomodate a higer density of vehicles at free-flow conditions after the change. Ongoing assessment of the ramp metering implementation will allow the systems' calibrations to adjust to changing demand over time.
