Evaluation of safety effects of roundabouts in the Region of Waterloo: inclement weather and conversion

Abstract

Roundabouts, as a form of intersection traffic control, significantly improve safety and efficiency. In Canada, the benefits of roundabouts have drawn growing interest, and roundabouts are being constructed increasingly in recent years. However, compared with the popularity of roundabouts in other western countries, the Canadian experience with roundabouts is limited. To enhance the understanding of the safety of roundabouts both overall and during inclement weather, this research first provides risk estimates of collision occurrence at roundabouts and signalized intersections under inclement weather conditions relative to clear weather condition by using the matched-pair approach. This method reasonably controls for the effect of time-dependent variables by assuming that travel patterns are similar from one week to the next. Secondly, the empirical Bayes approach is used to analyze the safety effect of converting signal-controlled intersections to roundabouts. This method is able to estimate the safety impact of the conversion without the disadvantage of the regression-to-mean bias. There is no evidence of a statistically significant increase in crashes on days with rainfall relative to ‘good’ weather conditions for roundabouts, whereas there is evidence of such an increase in crash risk estimated to be 7 to 36 percent for signalized intersections. In addition, roundabout installation is shown as an effective safety prevention for severe collisions in the Region of Waterloo. However, roundabouts experience increases in total collisions both overall and during days with precipitation. The results of this study offer explanations regarding the effect of inclement weather on roundabout safety and the safety implications of the conversion from conventional signalized intersections to modern roundabouts in the Region of Waterloo.