Safety Effect of Roundabout Conversions in the United States: Empirical Bayes Observational Before-After Study

Abstract

Modern roundabouts are designed to control traffic flow at intersections without the use of stop signs or traffic signals. U.S. experience with modern roundabouts is rather limited to date, but in recent years there has been growing interest in their potential benefits and a relatively large increase in roundabout construction. This interest has created a need for data regarding the safety effect of roundabouts. Changes in motor vehicle crashes following conversion of 23 intersections from stop sign and traffic signal control to modern roundabouts are evaluated. The settings, located in seven states, are a mix of urban, suburban, and rural environments with the urban sample consisting of both single-lane and multilane designs and the rural sample consisting of only single-lane designs. A before-after study was conducted using the empirical Bayes procedure, which accounts for regression to the mean and traffic volume changes that usually accompany conversion of intersections to roundabouts. For the 23 intersections combined, this procedure estimated highly significant reductions of 40 percent for all crash severities combined and 80 percent for all injury crashes. Reductions in the numbers of fatal and incapacitating injury crashes were estimated to be about 90 percent. In general, the results are consistent with numerous international studies and suggest that roundabout installation should be strongly promoted as an effective safety treatment for intersections. Because the empirical Bayes approach is relatively new in safety analysis, the potential of this methodology in the evaluation of safety measures is demonstrated.

Externality of risk and crash severity at roundabouts

“…Generally, it was found that roundabouts are able to reduce injury crashes considerably, although not for all user groups (Daniels et al, 2008;2009;Elvik, 2003;Persaud et al, 2001). In a previous analysis by the same authors, crash prediction models were fit for all injury crashes at roundabouts (Daniels et al, 2010.).…”

Thermal behaviour of arsenic trioxide adsorbed on activated carbon

“…The value of roundabouts as an effective measure to reduce injury crashes for the full range of road users has been well established (De Brabander, Nuyts, & Vereeck, 2005;Elvik, 2003;Persaud, Retting, Garder, & Lord, 2001). However, the contrast with the effects on the subgroup of crashes with bicyclists is remarkable and may cause a dilemma in policy making.…”

Understanding Safety-Related Issues for Pedestrians at Modern Roundabouts

“…Crash and injury statistics indicate a significant reduction in all and injury crashes as a result of the installation of roundabouts due to the elimination of some vehicular conflict points and to lower entry speeds of vehicles by the features of the design both for urban and for rural settings (Maycock & Hall, 1984;Alphand et al, 1991;Arndt, 1998;Flannery & Datta, 1996;Guichet, 1997;Persaud et al, 2001;Retting et al, 2001;De Brabander et al, 2005;Rodegerdts et al, 2007;Isebrands, 2009). Where roundabouts replaced intersections under stop or traffic signal control, large reductions were found in injury crashes (76 percent), especially those involving fatal injuries (90 per cent); however, crash reductions are most pronounced for cars, less pronounced for other modes .…”