Study Details

Study Title: Safety Effectiveness of Converting Signalized Intersections to Roundabouts

Authors: Gross et al.

Publication Date:JAN, 2012

Abstract: Roundabouts may be new builds but often are conversions from existing intersections. When contemplating the later, there is a need to estimate the safety effects of conversions. Several studies have estimated large reductions in crashes and severity; however, these results pertain mainly to conversions from unsignalized intersections. Results for conversions from signalized intersections have been less conclusive. The objective of this study was to estimate the safety effectiveness of converting signalized intersections to roundabouts. Several States helped to identify signalized intersections that were converted to roundabouts in the recent past. In total, 28 conversions were identified in the United States. The empirical Bayes (EB) method was employed in an observational before-after study to estimate the safety effects. Data from select States were also used in a cross-sectional analysis to investigate the compatibility of results from cross-sectional and before-after studies. The EB results indicated a safety benefit for converting signalized intersections to roundabouts. There were reductions in both total and injury crashes, with a larger benefit for injury crashes. Further analysis indicated that the safety benefit of roundabouts for total crashes decreased as traffic volumes increase, a result that suggests the need for the development of a crash modification function, a task for which more data would be required. The safety benefit for injury crashes was sustained across all traffic volumes. Both trends were supported by the cross-sectional analysis. Based on the analysis, it appears that roundabouts have the potential to significantly reduce crashes and severity at signalized intersections.

Study Citation: Gross, F., Lyon, C., Persaud, B., Srinivasan, R., "Safety Effectiveness of Converting Signalized Intersections to Roundabouts." Presented at the 91st Annual Meeting of the Transportation Research Board, Paper No. 12-1658, Washington, D.C., (2012) Results also published in Accident Analysis and Prevention, Volume 50, January 2013, pages 234-241.

CMFs Associated With This Study

Category: Intersection geometry

Countermeasure: Conversion of signalized intersection into single- or multi-lane roundabout

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.81194 StarsAllAllNot SpecifiedUrban and suburban
0.29713 StarsAllA,B,CNot SpecifiedUrban and suburban
0.74263 StarsAllAllNot SpecifiedUrban and suburban
0.45553 StarsAllA,B,CNot SpecifiedUrban and suburban

Countermeasure: Convert signalized intersection to modern roundabout

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.79214 StarsAllAllNot SpecifiedUrban and suburban
0.34664 StarsAllA,B,CNot SpecifiedUrban and suburban
0.58424 StarsAllAllNot SpecifiedSuburban
0.26743 StarsAllA,B,CNot SpecifiedSuburban
1.15-153 StarsAllAllNot SpecifiedUrban
0.45553 StarsAllA,B,CNot SpecifiedUrban
1.07-73 StarsAllAllNot SpecifiedUrban and suburban
0.37633 StarsAllA,B,CNot SpecifiedUrban and suburban
0.76244 StarsAllAllNot SpecifiedUrban and suburban
0.34663 StarsAllA,B,CNot SpecifiedUrban and suburban