Louisiana currently has 30 roundabouts in operation and hundreds of roundabouts in the planning and design stage. The Louisiana Department of Transportation and Development (DOTD) is very interested in knowing 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 layout of intersection, and nighttime 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 changes in the number of conflicting points and traffic control method, it is understandable why the most significant and consistent safety improvement was associated with the roundabouts previously controlled by stop signs on minor streets. 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 its safety benefit alone based on the benefit-cost ratio analysis for this group of roundabouts.
The study did identify a few compounding factors at the individual intersections, such as questionable geometric design elements, increased number of conflicting points, unpredictable human behavior, and lack of lighting at night.
|Commitee:||Gang, Daniel, Khattak, Mohammad Jamal, McManis, Kenneth|
|School:||University of Louisiana at Lafayette|
|School Location:||United States -- Louisiana|
|Source:||MAI 57/05M(E), Masters Abstracts International|
|Subjects:||Civil engineering, Transportation|
|Keywords:||Crash modification factor, Design details, Empirical bayes, Highway safety, Roundabout|
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