Ring around the roadway: When to use a roundabout

Posted in: Highways


Roundabout-1_bodyConventional intersections are not always the best solution to meet the increasingly complex traffic problems we face today. When solving challenges associated with limited sight and irregular traffic patterns, a roundabout is oftentimes a viable intersection option.

We’ve already discussed how roundabouts can benefit your community in “The many benefits of roundabouts,” but there are many factors that go into determining if a roundabout is right for your intersection. Crucial safety and operational concerns are frequently remedied by this type of intersection as compared to other conventional intersections.

Roundabouts may not exceed in performance for all factors that are considered, but neither will the conventional option. Each intersection has its own unique set of needs and priorities. During the preliminary engineering phase of a project, all of the factors of the intersection should be explored to understand how each alternative performs relative to its unique needs. The key to determining whether a roundabout will work for your intersection is to identify which needs are the most important and then compare the benefits that a roundabout may or may not provide.

For example, an intersection with heavy flows during only a few hours of the day may afford lower daily delay because of the continuous flow of traffic that a roundabout provides. And we say “why stop when you can go?” – compared with full stops incurred at signalized intersections during off-peak hours, drivers may be pleased that roundabouts eliminate unnecessary pauses in their travel.

Roundabout-2_bodyIntersections with limited sight distance are strong candidates for roundabouts. Sight distance is intentionally limited to assist with controlling speeds. Access to adjacent businesses may need to be removed or relocated to provide space for signal queues, but shorter vehicle stacking at a roundabout gives better access and visibility for those access points.

Public acceptance takes time and effort, this is an important component of the project that deserves considerable attention. Having analytical data that supports the benefits of roundabouts helps the public accurately understand the alternative’s performance and impacts. Public opinion can make or break a project, so having comparison data for alternatives can prove to be invaluable when demonstrating the pros and cons of a roundabout. Chances are that a roundabout has solved a similar problem elsewhere. Being able to demonstrate the key details of the solution with graphics and video is a convincing rationale to demonstrate that roundabouts are not “experimental”.

Roundabouts are an excellent solution for many intersection concerns. They provide safety for both motorists and pedestrians alike, and their visual appeal will create an intersection that the public will be proud to have in their community.  But what if roundabouts are not the best option, and how do you decide? We’ll dive deeper into the comparison data used to choose intersection types in the weeks to come.


Troy Pankratz, PE

About the Author

Troy Pankratz, P.E., has designed hundreds of roundabouts across the country using his expertise in intersection geometry to produce designs that elevate his clients’ investment. He absorbs the details of a project’s objectives, so he can work to develop ideal solutions. Troy finds educating and informing project stakeholders about innovative intersections particularly rewarding.

Read more posts by Troy Pankratz, PE