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Alternative Designs to Alleviate Freeway Bottlenecks at Merging, Diverging, and Weaving Areas

Monday, June 8, 2020 - 14:15

Alternative intersections and interchanges brought major benefits to the United States during the 2008–2018 time period. Given the positive impacts, it stands to reason that similar breakthroughs might be possible at freeway merge and diverge locations. This report describes the outcomes of a project that examined this possibility. The primary tool of evaluation was sensitivity analysis via microscopic traffic simulation, also known as microsimulation. The split merge design, and the positioning of managed lanes on the right side of the freeway, are two unrelated designs that showed excellent promise (in terms of benefit—cost ratio). Coordinated ramp metering did not show significant additional benefits beyond conventional asservissement lin’eaire d'entr’ee autorouti‘ere, also known as ALINEA, metering. Speed optimization showed excellent benefits but only during narrow ranges of traffic congestion. Mainline metering also showed reasonably good benefits but could be challenging to implement. It is conceivable that speed optimization and mainline metering could produce more favorable benefit—cost ratios if they could be implemented via connected and automated vehicle (CAV) technologies. However, the split merge and right-side managed lane designs produced excellent benefits without the need for CAV technologies. This report is available from the US FHWA at https://www.fhwa.dot.gov/publications/research/operations/20008/20008.pdf