Safety effectiveness of converting signalized intersections to roundabouts

Area of Science:

• Traffic Engineering
• Road Safety
• Transportation Planning

Background:

• Roundabouts are increasingly used as alternatives to traditional intersections.
• Existing safety research primarily focuses on conversions from unsignalized intersections.
• Data on the safety effectiveness of converting signalized intersections to roundabouts is limited and dated.

Purpose of the Study:

• To estimate the safety effectiveness of converting signalized intersections to roundabouts.
• To address the knowledge gap regarding roundabout conversions from signalized intersections.
• To analyze safety effects across varying traffic volumes.

Main Methods:

• Observational before-after study using the empirical Bayes (EB) method.
• Analysis of 28 signalized intersection conversions to roundabouts in the United States.
• Cross-sectional analysis to compare with before-after study results.

Main Results:

• Significant reductions in total and injury crashes were observed after conversion.
• Injury crash reductions were more pronounced and consistent across traffic volumes.
• Total crash reduction benefit decreased with increasing traffic volume, suggesting a need for crash modification functions.

Conclusions:

• Converting signalized intersections to roundabouts offers substantial safety benefits, particularly for injury crashes.
• Roundabouts are a viable strategy for improving safety at complex intersections.
• Variability in treatment effects across sites highlights the need for further research and data collection.