The concept of mini-roundabout has gained popularity in the United Kingdom and many other European countries over the past decade. Like roundabouts, mini-roundabouts are a type of intersection rather than merely a traffic calming measure, although they may produce some traffic calming effects. They are best suited to environments where speeds are already low and environmental constraints would preclude the use of a larger roundabout with a raised central island. The regular roundabouts are considered to be safer than intersections, better suited for traffic calming, reducing delay, and thereby reducing the emissions. However, the safety benefits associated with mini-roundabouts are not well documented and must be evaluated for engineers to consider for more mini-roundabout installations. The objectives of the proposed research project are: 1) to identify a significant sample of mini-roundabout locations in the United States, 2) to collect before and after crash data at the existing mini-roundabout locations, 3) to conduct a before and after study for determining safety benefits of mini-roundabouts, and, 4) to compute crash modification factors (CMFs) for mini-roundabouts based on before and after crash data and cross-sectional design.
The proposed scope of work involves 1) reviewing past research and current practices on developing CMFs for mini-roundabouts and roundabouts, in general, 2) identifying mini-roundabout installation locations in North Carolina and in the United States, 3) collecting before and after traffic characteristics data, crash data, and network and off-network characteristics data, 4) developing CMFs for selected types intersections that are converted to mini-roundabouts, and, 5) preparing and submitting a final report. The focus will be primarily on mini-roundabout locations with preferred characteristics of interest to North Carolina Department of Transportation, NCDOT (1. single-lane roundabouts without slip lanes, 2. speed limit greater than or equal to 35 mph, and, 3. rural areas or other locations with similar characteristics).