Study Details

Study Title: Safety Evaluation of Roundabouts in Georgia

Authors: Gbologah et al.

Publication Date:JAN, 2019

Abstract: U.S. Roundabout growth have been significant in recent years and many published studies have documented significant safety benefits of roundabouts. However, the safety benefits for a roundabout may vary from region to region depending many local factors. Therefore, transportation agencies can make more informed implementation decisions with local safety evaluations rather than published national findings. However, roundabouts are relatively new in the United States and most DOTs, including Georgia, are often hindered by the data availability requirements of the state-of-the-art empirical Bayes analysis evaluation procedure. This current study provides a safety evaluation of 23 Georgia roundabouts. It adopts a time-dependent form of the Highway Safety Manual predictive (empirical Bayes) method to estimate potential crash reductions across all crashes and all injury/fatal crashes. The method extends the empirical Bayes procedure towards a full Bayesian analysis. The findings indicate a 37-48 percent reduction in average crash frequency for all crashes and a 51-60 percent reduction in average crash frequency for injury/fatal crashes at four-leg roundabouts that were converted from stop-controlled and conventional intersections. In addition, when analyzed as a group, three-leg and four-leg roundabouts converted from stop-controlled and conventional intersections collectively experienced 56 percent reduction in average crash frequency for all crashes and 69 percent reduction in injury/fatal crashes. The study did not consider five-leg roundabouts due to small sample size and concerns about the form of the SPF. The adopted methodology offers DOTs with data availability challenges an alternative evaluation framework that retains the positive attributes of empirical Bayes analysis.

Study Citation: Gbologah, F. E., A. Guin, and M.O. Rodgers. "Safety Evaluation of Roundabouts in Georgia". Presented at the 98th Annual Meeting of the Transportation Research Board, Paper No. 19-02900, Washington, D.C., (2019).

CMFs Associated With This Study

Category: Intersection geometry

Countermeasure: Conversion of intersection to roundabout

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.62337.73 StarsAllAllNot specifiedAll
0.61338.73 StarsAllAllNot specifiedAll
0.64235.83 StarsAllAllNot specifiedAll
0.50949.13 StarsAllK,A,B,CNot specifiedAll
0.51248.83 StarsAllK,A,B,CNot specifiedAll
0.46753.33 StarsAllK,A,B,CNot specifiedAll
0.50349.73 StarsAllAllNot specifiedAll
0.49550.53 StarsAllAllNot specifiedAll
0.54945.13 StarsAllAllNot specifiedAll
0.40359.73 StarsAllK,A,B,CNot specifiedAll
0.40559.53 StarsAllK,A,B,CNot specifiedAll
0.39160.93 StarsAllK,A,B,CNot specifiedAll
0.43956.13 StarsAllAllNot specifiedAll
0.43356.73 StarsAllAllNot specifiedAll
0.31368.73 StarsAllK,A,BNot specifiedAll
0.30969.13 StarsAllK,A,B,CNot specifiedAll