Mini-roundabouts, while smaller than standard roundabouts, function similarly. Roundabouts are circular, unsignalized intersections where all traffic moves in a counterclockwise direction around a central island. Unlike regular roundabouts, mini-roundabouts have an Inscribed Circle Diameter (ICD) of 90 feet or less. With this smaller ICD, the central island and all splitter islands are of a mountable design that is typically two and a half to three inches in vertical height, making them traversable, or they are painted.
Mike Vaughn of the Kentucky Transportation Cabinet (KYTC) references an old adage when explaining mini-roundabouts. “As the saying goes, ‘There is a time and place for everything.’ Mini-roundabouts are small and the small footprint means a mini-roundabout cannot process as many vehicles per hour as a regular sized roundabout…Mini-roundabouts work best in locations with low overall traffic volumes, low truck traffic, and low speed.”
When designing a standard roundabout, large truck traffic is a priority; conversely, if you’re planning a mini-roundabout, the focus is on the rest of the traffic: smaller, more common vehicles. Both types of roundabouts provide traffic calming benefits, employ pedestrian safety measures, and can be used in various scenarios and circumstances.
FHWA highlights many benefits of mini-roundabouts in their technical study. As Vaugh alluded, mini-roundabouts may not always be the best solution, but there are many circumstances in which mini-roundabouts fit the bill. Overall the popularity of mini-roundabouts is growing due to these compelling factors:
Compact Size – A mini-roundabout is often compact enough to fit into an existing intersection.
Operational Efficiency – Mini-roundabouts keep traffic flowing steadily.
Traffic Safety – Studies show that crash rates are lower in mini-roundabout intersections.
Traffic Calming – As speeds are reduced on roundabouts, they can often produce traffic calming effects.
Access Management – Mini-roundabouts can provide access to up-and-coming residential or commercial developments.
Environmental Benefits – Fuel consumption and vehicle emissions are reduced with utilization of mini-roundabouts.
Mini-Roundabouts in Connecticut
Although Connecticut has been constructing more roundabouts in recent years, mini-roundabouts are still a new tool. Below are two examples of mini-roundabouts found in the state: one with traversable stamped center and splitter islands and one painted.
For more information and assistance with local road safety in your community, contact Melissa Evans, Safety Circuit Rider, at firstname.lastname@example.org.
Portions reprinted with permission from the Fall 2021 issue of the Kentucky Technology Transfer newsletter, The Link, a publication of the Kentucky Local Technical Assistance Program (LTAP) at the University of Kentucky Transportation Center.
Mini-Roundabouts: Technical Summary, FHWA-SA-10-07, https://nacto.org/wp-content/uploads/2015/04/fhwasa10007_MiniRoundabouts.pdf