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What is a roundabout?


A modern roundabout is an unsignalized, circular intersection engineered to maximize safety and minimize traffic delay. Over the last few decades, tens of thousands of roundabouts have been installed in Europe, Australia and other parts of the world. Recently, they have gained support in the United States, including communities in Iowa. From 1999 to 2009, at least 33 modern roundabouts were constructed in Iowa.

Iowa roundabout photo
Iowa roundabout - Photo credit Hillary Isebrands

Drivers in Iowa are becoming more comfortable using roundabouts in the communities that have them. In the cities and counties where roundabouts have been built, even in locations where the public had been hesitant about accepting them initially, roundabouts ultimately have been accepted enthusiastically because of the increased safety they provide, along with traffic calming, and environmental and aesthetic benefits.

Roundabouts differ from the old, larger traffic circles and rotaries in three major areas.

Roundabout graphic
  1. A roundabout is generally smaller in diameter, requiring lower traveling speeds.

  2. At roundabouts, the entering traffic yields the right-of-way to the circulating traffic. This yield-at-entry rule keeps traffic from locking up and allows the free flow movement.

  3. The splitter and center islands of a roundabout deflect entering traffic and reinforce the yielding process.


The majority of modern roundabouts operate very efficiently with single-lane approaches and a single circulating lane. In cases where certain movements need to carry higher traffic volumes, roundabouts can be designed with multiple lanes. Modern designs include signing, pavement markings and design features that can guide multiple lanes through a roundabout without the old problem of becoming “trapped” in the center lane.