United States Department of Transportation
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Evaluation of Adaptive Ramp Metering on I-80 in the San Francisco Bay Area
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2018-09-01
[PDF-4.55 MB]
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Edition:Final
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Abstract:Adaptive ramp metering (ARM) is a critical component of smart freeway corridors under an active traffic management portfolio. While improving capacity through smart corridors and application of proactive traffic management solutions is less costly and easier to deploy than freeway widening, conversion to smart corridors still represents a sizable investment for public agencies. However, in the U.S. there have been limited evaluations, of smart corridors in general and ARM in particular, based on real operational data. This project examined recent Smart Corridor implementation on I-80 in the Bay area based on travel time reliability measures, efficiency measures, and based on user opinion survey. As such, the evaluation represents the most complete before/after evaluation of such systems. The study section is 19 miles long and extends between the Carquinez Bridge at Crockett at its east end and the San Francisco-Oakland Bay Bridge at its west end. The reliability measures include buffer index, planning time, and measures from the literature that account for both skew and width of the travel time distribution. For efficiency, the ratio between vehicle miles traveled/vehicle hours traveled (VMT/VHT) is estimated for the I-80 corridor. All before-after comparisons are contextualized through similar measures from another Bay area corridor I-680, which did not go through a Smart Corridor Implementation. The measures are estimated for the entire corridor as well as corridor segments upstream of a bottleneck that historically have the worst measures of reliability. User-opinion survey conducted as part of the project involved 626 completed and usable survey responses covering a wide yet representative demographic of users. The representative survey was ensured using an induced exposure approach adopted from traffic safety literature. The results show that the marginal improvements in freeway operations based on reliability and efficiency are underappreciated by the users.
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