Study Details

Study Title: Safety of Roundabout: The Details Matter

Authors: Sun et al.

Publication Date: 2018

Abstract: Louisiana currently has 30 roundabouts in operation and hundreds of roundabouts in the planning and designing stage. The state Department of Transportation and Development (DOTD) is very interested to know the safety performance of existing roundabouts in the state. As revealed in this paper, the safety effectiveness of a roundabout depends on its prior traffic control type, conformity to the geometric design guidelines, changes in intersection’s layout, and night-time lighting conditions. All 19 roundabouts investigated by this study demonstrated significant reduction in injury crashes because of lower operating speed, reduced right-angle collisions, and elimination of head-on and left-turn crashes. Based on the changes in the number of conflicting points and traffic control method, it is understandable why the biggest and most consistent safety improvement were associated with the roundabouts previously controlled by stop-sign on minor street. The Crash Modification Factor (CMF), as estimated by the Empirical Bayes (EB) method, for this group of roundabouts, is 0.28 with a standard deviation of 0.054. The roundabout is economically justified for the safety benefit alone based on the benefit-cost ratio analysis for this group of roundabouts. Although the other roundabouts, grouped by prior traffic control type and layout change, did not show consistent crash reduction, the study did identify a few compounding factors at the individual intersections, such as the questionable geometric design elements, increased number of conflicting points, human behavior and lack of lighting at night.

Study Citation: Sun, X., Y. He, M.A. Rahman, and K. McManis. "Safety of Roundabout: The Details Matter". Presented at the 97th Annual Meeting of the Transportation Research Board, Paper No. 18-00871, Washington, D.C., (2018).

Study Report: Download the Study Report Document


CMFs Associated With This Study

Category: Intersection geometry

Countermeasure: Convert intersection with minor-road stop control to modern roundabout

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.28 72 3 Stars All All Not specified Urban and suburban