Roundabouts in Engineering

In honor of National Roundabout Week, we’re sharing a throwback blog from 2016! A few years have passed since it was last published, but one thing remains the same – roundabouts are a proven safety countermeasure because they can substantially reduce crashes that result in serious injury or death. Roundabouts can improve safety, promote lower speeds and traffic calming, reduce conflict points, lead to improved operational performance, and meet a wide range of traffic conditions because they are versatile in size, shape, and design.

You’ve probably noticed more roundabouts popping up around your community and neighborhood, and we believe this trend is here to stay. Since 2016, our team has considered the feasibility of roundabouts at numerous intersections throughout the state of Alabama. We’ve also been selected to prepare design plans for a dozen roundabouts across the state during that time. Some of these are currently under construction, and others should be arriving soon. As more of those projects are completed, we’ll post pictures and a few lessons learned along the way.

Although Alabama does not have as many roundabouts as some of its neighboring states, such as Florida or Georgia, these intersections are becoming more common throughout the state. This increase is likely connected to the Alabama Department of Transportation’s (ALDOT) 2015 release of a Roundabout Planning, Design, and Operations Manual providing the framework and guidance for bringing more roundabouts to the state.

Unlike traditional signalized or stop-controlled intersections, roundabouts are circulatory intersections in which entering traffic yields to vehicles circulating a central island or exiting the roundabout. Once entering the roundabout, traffic moves in a counterclockwise direction. When driving in a roundabout, it’s important to remember to yield to traffic approaching from your left.

Roundabouts have several significant benefits: they can increase efficiency, have a more pleasing aesthetic appearance, and require less maintenance. In many cases, roundabouts are also less costly to construct. But the greatest benefit of selecting a roundabout for intersection control is safety performance. According to the American Association of State Highway and Transportation Officials (AASHTO) Highway Safety Manual, they reduce the potential for fatal or injury crashes by close to 80 percent, when compared with traditional signal or stop-controlled intersections. This reduction in serious crashes results from their unique design characteristics that remove left-turn movements and keep vehicles traveling at similar low speeds through the intersection.

The Federal Highway Administration (FHWA) and AASHTO have written informational guides about the design and analysis of roundabouts. These are generally recognized as the industry standard. ALDOT’s Roundabout Planning, Design, and Operations Manual provides guidelines and recommended practices for planning and designing roundabouts within Alabama.