Developing Crash Modification Factors for Mini-Roundabouts
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2023-04-01
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Edition:Final Report
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Abstract:This study evaluated the safety effectiveness of mini-roundabout (MR) installations at two-way stop-controlled (TWSC) and all-way stop-controlled (AWSC) locations. Based on a longitudinal design including comparison sites, the database included three States: Washington, Michigan, and Maryland. Safety data were compiled for locations of known MR installations where the date of installation and prior intersection condition were known. Suitable comparison locations were included. The study included 15 MR locations from Washington, 6 from Michigan, and 6 from Maryland. Crash data from 2003 through 2019 were available from Washington, data from 2013 through 2019 from Michigan, and data from 2015 through 2019 from Maryland. A fully Bayesian evaluation based on the Washington crash data estimated crash reductions for MR converted from TWSC ranging from 31 to 42 percent for various crash types, which were statistically significant. The study found a statistically significant reduction of 39 percent in multivehicle crashes at MR converted from AWSC intersections from an additional analysis based on the complete database from all three States. This study also produced benefit–cost ratios of 2.88 and 2.87 for MR conversions from TWSC and AWSC, respectively, when only safety benefits were considered, whereas the ratio was 13.41 for AWSC intersections when operational benefits were also considered. These results indicate economic feasibility of MR installations.
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