The number of crashes at two-lane roundabouts reduces as drivers become more familiar with them, a new study has suggested.

The Insurance Institute for Highway Safety (IIHS) looked a crash trends at both single and two-lane roundabouts in Washington built between 2009 and 2015.

Researchers found the number of crashes at two-lane roundabouts decreased on average nine percent per year, while the odds that a crash involved a serious injury decreased by nearly one-third annually.

The number of crashes increased on average seven percent at single-lane roundabouts, and the odds of an injury fell 19 percent annually.

“Two-lane roundabouts are inherently more complex than the single-lane type,” said Wen Hu, IIHS Senior Research Transportation Engineer. “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.”

The study said traffic engineers “shouldn’t rely on drivers to learn how to navigate roundabouts on their own,” and said better design could help people drive through a roundabout safely the first time they encounter it.