Study Details

Study Title: A Statistical Analysis and Development of a Crash Prediction Model for Roundabouts on High-Speed Rural Roadways

Authors: Isebrands

Publication Date: JAN, 2012

Abstract: Roundabouts have proven to be effective in urban and suburban environments in the United States, but little has been reported on their effectiveness in rural environments with high-speed roadways. There is no question that roundabouts reduce 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 (19) in a rural environment with high speed approaches. The findings validated the hypothesis and descriptive statistics that roundabouts in a rural environment out perform other intersection safety improvements as well as roundabouts in urban and suburban environments. A before and after crash analysis was conducted for the nineteen intersections using a negative binomial regression model. Results showed statistically significant reductions for both 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 67% reduction in total crashes and a 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 planning level crash prediction models for both total and injury crashes at rural roundabouts on high-speed roadways which supplement the models produced in NCHRP Report 572 Roundabouts in the United States and will be considered for inclusion in the next edition of the AASHTO Highway Safety Manual.

Study Citation: Isebrand, H. "A Statistical Analysis and Development of a Crash Prediction Model for Roundabouts on High-Speed Rural Roadways." Presented at the 91st Annual Meeting of the Transportation Research Board Paper No. 12-4191, Washington, D.C., (2012). Earlier study: Isebrands, H. "Crash Analysis of Roundabouts at High-speed Rural Intersections." TRB 88th Annual Meeting Compendium of Papers CD-ROM. Washington, D.C., (2009).


CMFs Associated With This Study

Category: Intersection geometry

Countermeasure: Convert high-speed rural intersection (3 leg) to roundabout

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.74 26 3 Stars All All Not specified Rural
0.28 72 3 Stars All A,B,C Not specified Rural

Countermeasure: Convert high-speed rural intersection (4 leg) to roundabout

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.32 68 4 Stars All All Not specified Rural
0.12 88 4 Stars All A,B,C Not specified Rural
0.26 74 4 Stars All All Not specified Rural
0.11 89 4 Stars All A,B,C Not specified Rural
1.41 -41 3 Stars All All Not specified Rural
0.4 60 3 Stars All A,B,C Not specified Rural

Countermeasure: Convert high-speed rural intersection to roundabout

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.33 67 4 Stars All All Not specified Rural
0.13 87 4 Stars All A,B,C Not specified Rural
0.17 83 3 Stars Angle All Not specified Rural
0.85 15 3 Stars Rear end All Not specified Rural
0.09 91 3 Stars Angle A,B,C Not specified Rural
0.54 46 2 Stars Rear end A,B,C Not specified Rural
2.79 -179 3 Stars Sideswipe All Not specified Rural
4.66 -366 3 Stars Fixed object All Not specified Rural