By Vern Swing, PE
The entire team at Spack Consulting are proponents of roudabouts, and we have written extensively on the topic. But as roundabouts take hold in the US, more design ideas are coming forward on their application to improve traffic flow and improved pedestrian safety. This includes the use of mini roundabouts, which was the topic of a webinar I recently attended. Put on by the Transportation Research Board’s (TRB) subcommittee on roundabouts, the two-hour webinar was fully devoted to mini-roundabouts and if the US was ready to take advantage of their benefits.
The webinar featured four speakers who discussed their application of mini-roundabouts to address existing capacity and safety problems. The take home message repeated by all four presenters could be boiled down to the following:
- Small Footprint. Mini-roundabouts had reduced diameters which allowed them to fit within existing right of ways, typically ranging from 45 feet to 90 feet.
- Cost-Effective. The construction cost for mini-roundabouts was approximately $250,000-$350,000 with basically no right of way acquisition cost. This compares favorably with typical roundabout construction cost north of a $1,000,000.
- Short Development Time. Construction time for the mini’s is generally 2-3 weeks.
- Similar Design to Large Roundabouts. In all cases the geometric layout was like regular roundabouts in terms of deflection islands and left centric approaches.
- Improved Traffic Flow and Pedestrian Safety. The results of the installations did result in improved capacity, improved pedestrian safety and large reduction in injury crashes.
In our opinion this is an intersection control treatment that should be included in the toolbox when evaluating mitigation for congestion and/or safety issues. And yes, according to the webinar, we are ready to start realizing the benefits of mini-roundabouts.
Interested in more information about roundabouts? Check out these great resources:
- Video: Traffic Corner Webinar | Are Roundabouts a Silver Bullet to Traffic Issues?
- Free Traffic Corner Tuesday webinars
- Roundabout Capacity Analysis Spreadsheet