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How Do Roundabouts Impact Crash Rates and Road Safety?
In transportation departments throughout the United States, civil engineers and planners look at crash data to find the most dangerous sections of the road and adjust their designs to save lives.
You might not know it, but you drive through quite a few of those dangerous road features every day: intersections. In fact, about 2,300 people die every year at signalized intersections according to the U.S. Department of Transportation.
Because intersections are the site of so many deaths, state legislators and transportation experts have been investigating new approaches to road design, including the intersection's intriguing cousin, the roundabout.
Roundabouts popularity in Europe
European areas have a reputation for loving roundabouts. In the United Kingdom, there's even an official British Roundabout Appreciation Society.
It's taken longer for American cities to embrace them.
Although commentators speculate why roundabouts have only sporadically caught on in the United States, one reason may be widespread misinformation about what roundabouts are and their effectiveness at preventing car crashes.
Circular road features
Roundabouts are often confused with circular intersections, rotaries and neighborhood traffic circles.
"The rotary is usually larger and serves a wider geographic function, with parking or other features occupying the center island," according to a National Cooperative Highway Research Program report. "The large traffic circle likewise functions as more of a circular confluence of streets, often allowing and encouraging pedestrians to access the center of the circle."
In contrast to rotaries, roundabouts do not include pedestrian access or parking. Another type of circular traffic feature, the neighborhood traffic circle, is small and slows traffic by narrowing available travel lanes.
Characteristics of roundabouts
The unique features of roundabouts are what make them effective at preventing collisions. The defining features are counterclockwise flow, entry yield control and low speed limits. They can be single-lane or multilane.
The goal is to force drivers to pay attention and slow down. They cannot speed through so have to enter slowly and yield to other drivers already in the roundabout. This goal can be met by multiple shapes of roundabouts, too.
"Roundabouts don't even need to be perfectly circular!" the Washington State Department of Transportation says. "Successful roundabouts come in all shapes and sizes. Some are oval-, teardrop-, peanut- and dogbone-shaped. Some have as few as three legs and others as many as six."
Data about roundabout safety
The reason so many traffic safety leaders and civil engineers tout the roundabout as America's solution to intersection carnage is in the data.
"Significantly, roundabouts reduce the types of crashes where people are seriously hurt or killed by 78-82 percent when compared to conventional stop-controlled and signalized intersections," the AASHTO Highway Safety Manual says.
That means, when cities and counties construct roundabouts when updating or building intersections, fewer people could die in collisions. A roundabout forces drivers to slow down, as they usually cannot go faster than 20-25 miles per hour.
"This is an effective design that moderates travel speeds at all times," according to the NCHRP. "This can proactively support a goal to slow vehicles traveling through the community, which also benefits pedestrians and cyclists."
Many federal and state agencies have been recommending roundabouts.
"Roundabouts should be considered as an alternative for intersections on federally funded highway projects that involve new construction or reconstruction," according to the Proven Safety Countermeasures findings by the U.S. Department of Transportation.
"Roundabouts should also be considered when rehabilitating existing intersections that have been identified as needing major safety or operational improvements. Roundabouts have also proven to be effective at freeway interchange ramp terminals and at rural high-speed intersections."