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Field Evaluation of a Restricted Crossing U-turn Intersection

出版	United States Department of Transportation, Federal Highway Administration, 2012
URL	http://books.google.com.hk/books?id=4WGF0AEACAAJ&hl=&source=gbs_api

註釋Four-lane divided highways are an economical design solution to increase the capacity of rural highways compared to grade-separated limited access facilities. Compared to two-lane undivided rural highways, four-lane divided highways have markedly lower rates of sideswipe, rear-end, and head-on collisions. However, right-angle crash rates are markedly higher on four-lane divided highway intersections than at two-lane undivided highway intersections, largely as a result of left-turn and through movements from minor roads conflicting with far-side vehicles on the divided highway. The restricted crossing U-turn (RCUT) intersection is a promising treatment to mitigate right-angle crashes where two-lane minor roads intersect with rural four-lane divided highways. This report includes a comparison of operations at an RCUT intersection in Maryland with a roughly comparable conventional stop-controlled intersection on the same corridor. It also includes before-after crash analyses for intersections converted from conventional to RCUT designs on two Maryland highway corridors. The operational analysis found that conflicts between vehicles entering or crossing the highway from a minor road were reduced, weaving movements were about the same for the two intersection types, the RCUT design added about 1 min to travel time for vehicles making left-turn or through movements from the minor road. Three approaches were used to estimate the affect of an RCUT conversion on crashes. All three approaches led to the same conclusion: the RCUT design reduces crashes. A simple 3-year before and 3-year after analysis suggested a 30 percent decrease in the average number of crashes per year. An analysis that adjusted the observed crash rate at RCUT locations for the observed crash rate at nearby conventional intersections on the same corridors suggested a 28 percent decrease in the average annual number of crashes. An empirical Bayes analysis that adjusts for, among other things, the expected number of crashes at similar intersections and average annual traffic suggested a 44 percent decrease in crashes. Furthermore, the analyses suggest an overall reduction in crash severity with the RCUT design.