The number of crashes at two-lane roundabouts decreased on average 9% per year of their existence in the roadway, according to a new study conducted by the Insurance Institute for Highway Safety.

In another finding, the odds that a collision at a two-lane roundabout involved an evident or incapacitating injury decreased by nearly one-third annually.

Failing to yield the right-of-way is a common problem at roundabouts in general. However, the study showed that the odds that a crash at a two-lane roundabout involved that type of error dropped 11% annually.

These latest findings indicate that as drivers get familiar with two-lane roundabouts, safety tends to increase.

Conducted in Washington state, which features more than 300 roundabouts, the study involved 98 single-lane and 29 two-lane roundabouts built between 2009 and 2015.

For each roundabout, IIHS looked at crashes beginning with the first full calendar year after completion and ending with 2016. Clearly, older roundabouts had more years of data. To account for the effects of the economy and traffic volumes on crashes, the analysis included the unemployment rate and annual vehicle miles traveled in the area where each roundabout was located.

The longest period analyzed for any of the roundabouts was seven years.

While the safety findings for two-lane roundabouts, which are often considered challenging to navigate, were encouraging. The single-lane roundabout findings were less significant.

The number of crashes increased an average of 7% at single-lane roundabouts, and the odds of an injury fell 19% annually, but those changes weren’t statistically significant, according to IIHS. It is not clear how long the crash reductions would be expected to continue.