Study Details

Study Title: Evaluating the Performance and Safety Effectiveness of Roundabouts


Publication Date:DEC, 2011

Abstract: This report documents the evaluation of the performance and safety effectiveness of roundabouts within the State of Michigan. The study began with the identification of roundabouts within Michigan. This was followed by collecting data on the geometric features of the roundabouts and crash history for each roundabout site from January 1, 2001 to December 31, 2010. The analysis of the roundabouts within Michigan included a literature review, a best practices review of other municipalities, an evaluation of the crash data (both a simple before and after and an Empirical Bayes (EB) analysis, and a site visit to a select group of roundabouts that was determined by the study team. The site visits included a speed study at several of the locations, a conflict analysis at several of the locations, and an assessment of overall operations of the roundabout, including noting any potential issues that may be observed from the operations of the roundabouts. Another finding of the analysis was an average cost savings that the various types of roundabouts are expected to have based on savings the reduction in delay and crash reduction. Additional findings from the site visits resulted in a rating of issues based on Collision Risk Assessment Method. Based upon the results of the EB analysis, Safety Performance Functions (SPFs) and Crash Modification Factors (CMFs) were established to reflect the roundabouts in Michigan. These are the first SPFs and CMFs that were developed to reflect the behaviors of Michigan roundabouts.

Study Citation: Bagdade, J. B.N. Persaud, K. McIntosh, J. Yassin, C.A. Lyon, C. Redinger, J. Whitten, and W.A. Butch, "Evaluating the Performance and Safety Effectiveness of Roundabouts." Report No. RC-1566, Michigan Department of Transportation, December 2011.

Study Report: Download the Study Report Document

CMFs Associated With This Study

Category: Intersection geometry

Countermeasure: Conversion of intersection to roundabout

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
1.346-34.65 StarsAllAllAllAll
0.58341.74 StarsAllA,B,CAllAll
1.002-0.24 StarsAllAllAllAll
0.48851.24 StarsAllA,B,CAllAll

Countermeasure: Conversion of signal-controlled intersection to roundabout

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.78321.74 StarsAllAllAllAll
0.3704 StarsAllA,B,CAllAll
1.975-97.55 StarsAllAllAllAll
0.80119.93 StarsAllA,B,CAllAll

Countermeasure: Conversion of stop-controlled intersection to roundabout

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
1.117-11.74 StarsAllAllAllAll
0.55844.24 StarsAllA,B,CAllAll
1.247-24.73 StarsAllAllAllAll
0.41958.14 StarsAllA,B,CAllAll
1.095-9.54 StarsAllAllAllAll
0.58141.94 StarsAllA,B,CAllAll
1.026-2.63 StarsAllAllAllAll
0.63636.43 StarsAllA,B,CAllAll