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Research: Roundabout Safety Improving

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July 12, 2019—IIHS researchers have found that crashes at two-lane roundabouts fall over time as drivers gain familiarity with them.

Roundabouts improve safety over traditional intersections, but the benefits of two-lane roundabouts have been less clear than those of single-lane roundabouts.

Roundabouts force drivers to slow down and all but eliminate the most severe types of intersection crashes — right-angle, left-turn and head-on collisions. Single-lane roundabouts see fewer total crashes of any type.

Adding another lane makes roundabouts more complex, creating more potential conflicts. Some studies have found smaller benefits when intersections with stop signs or traffic signals are converted to two-lane roundabouts than when they are converted to single-lane roundabouts. One 2012 study found that crashes actually increase after such conversions.

According to a study conducted by IIHS researchers on 98 single-lane and 29 two-lane roundabouts built between 2009 and 2015, the number of crashes at two-lane roundabouts decreased on average 9 percent per year.  The number of crashes increased on average 7 percent at single-lane roundabouts,

“Two-lane roundabouts are inherently more complex than the single-lane type,” says IIHS Senior Research Transportation Engineer Wen Hu, the study’s lead author. “Even in a place like Washington, many drivers still aren’t familiar with them, so it makes sense that there would be more crashes when a roundabout is first built than after it has been in place for a while.”

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