Abstract
Roundabouts have proved to be effective in urban and suburban environments in the United States, but little has been reported on the effectiveness of roundabouts in rural environments on high-speed roadways. There is no question that roundabouts reduce the speeds of all vehicles at intersections and reduce the frequency of fatal and injury-related crashes. This research is the first comprehensive look at roundabouts in a rural environment with high-speed approaches. Nineteen intersections had ample comprehensive crash data to be evaluated and analyzed for safety performance. The findings validated the hypothesis that roundabouts in a rural environment as well as roundabouts in urban and suburban environments outperformed other intersection safety improvements. A before-and-after crash analysis was conducted for the 19 intersections by using a negative binomial regression model. Results showed statistically significant reductions for the total number of crashes (63%) and injury crashes (88%) when roundabouts were implemented. A before-and-after empirical Bayes estimation was also conducted, and the results were consistent, indicating a 62% to 67% reduction in total crashes and an 85% to 87% reduction in injury crashes at these rural intersections. Furthermore, results showed that injury-producing crash types, such as the angle crash, were reduced by 91%, and were statistically significant. Finally, this research produced crash prediction models at planning level for total and injury crashes at rural roundabouts on high-speed roadways. This supplements the models produced in NCHRP Report 572: Roundabouts in the United States and reported in the AASHTO Highway Safety Manual.
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