What's 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. Since 1999, about a dozen roundabouts have been constructed in Iowa.
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.
- A roundabout is generally smaller in diameter, requiring lower traveling speeds.
- 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.
- The splitter and center islands of a roundabout deflect entering traffic and reinforce the yielding process.
There are various roundabout types designed according to the roadway characteristics and desired traffic movement. Low-capacity roundabouts have one circulating lane. Medium-capacity roundabouts have at least two circulating lanes. High-capacity roundabouts have at least three or four circulating lanes. Frequently, roundabouts are classified as hybrids, meaning that the circulating lane may have a portion that is one lane and a portion that is two lanes.
