Increasingly, roundabouts are the solution of choice for many intersections because they improve safety and traffic flow and reduce pollution due to less vehicle delays. Traditional roundabout design typically requires a larger footprint than a conventional four-way intersection.
Some local agencies are choosing to implement mini-roundabouts, which are characterized by a smaller diameter that fits within the dimension of a standard intersection. To accommodate large trucks and implements of husbandry, they feature fully traversable islands (central island and splitter islands). Currently, there are more than 40 mini roundabouts in Minnesota.
To help local agencies determine the type of roundabout to select for a particular site, the Minnesota Local Road Research Board developed Mini-Roundabouts FAQs, a guidance document that defines how mini and compact roundabouts fit in the toolbox and provides selection criteria for when to use each option.
What Did We Do?
The research team began by conducting a literature review to develop a comprehensive list of technical documents available on mini-roundabouts that could be synthesized into the guidance document. They gathered best practices from local agencies that have constructed mini-roundabouts and held focus groups with technical experts to review and answer FAQ questions and identify linkable resources.
“Mini-roundabouts are similar to traditional roundabouts operationally but there are factors that vary in their design. We looked at what was being done around the state, what worked, what didn’t, and summarized our findings into one best practices document,” said Jon Pratt, city engineer, City of Detroit Lakes. “It’s the kind of resource I wish I had access to when we were working on the roundabouts in Detroit Lakes.”
The team focused on addressing questions local agencies have about mini-roundabouts from understanding the difference between traditional, mini and compact roundabouts, to deciding which type of roundabout to use, to design features including details regarding the center treatment, safety considerations and best practices for winter maintenance.
They also looked at effective use of signage, education and outreach, and additional design resources.
What Was the Result?
Mini-Roundabout FAQs, a guidebook that synthesizes the information about mini-roundabouts into one easy-to-navigate format is now available. It also includes links to additional technical resources, lessons learned from local agencies, and detailed information about mini-roundabouts that have been constructed in Minnesota.
Crossroads 