The roundabout at Radio Drive and Bailey Road in Woodbury opened to traffic in November 2007.
At the end of August 2013, as part of a push to reduce crashes at the intersection, Washington County changed the east-west lane configuration.
Patch asked Joe Gustafson, Washington County transportation engineer, about the history of crashes at the site.
In addition to recording state-reported crashes at the roundabout, county officials also keep a running tally of Woodbury police responses, helping account for minor incidents in which officers arrive and there is little damage or no evidence of a crash.
Gustafson compiled the following information:
In the first five calendar years (2008-12) the roundabout was open to traffic, 82 crashes were reported to the state.
By comparison, the intersection at Radio Drive and Valley Creek Road saw 74 crashes during that timeframe, though that intersection has more traffic.
To adjust for volume, traffic officials usually talk about “crash rates” rather than total number of crashes, and by that measure, the Radio-Bailey roundabout had a crash rate of 2.72 per million entering vehicles (MEV), while Radio and Valley Creek had a crash rate of 0.91.
Gustafson noted that the numbers are not typical of roundabouts in general—roundabouts typically reduce crashes, especially injury crashes.
Including crashes that resulted in a police call but were not reported to the state because they were very minor, the roundabout averaged about 3.1 crashes per month (190 were reported over the five-year period).
Only six crashes from 2008-12 involved injuries, none of which were classified as serious. Many of those involved motorcycles.
Meanwhile, no crashes were reported when the roundabout’s south leg was closed this summer.
How They Happen
Of the police-reported crashes, about half were caused by a driver trying to merge into the roundabout instead of yielding to cross traffic.
Drivers usually saw each other and the yield sign, but misunderstood the roundabout’s design and treated their entry as a merge or a right turn instead of yielding to traffic from the left.
County officials have learned that two-by-two roundabouts have a higher crash potential, and thus made the change to a one-by-two configuration for Radio and Bailey. The new layout is meant to reduce violations that cause crashes.
The single-lane roundabouts in the county have operated well with regard to traffic flow and safety, according to Gustafson.
Included on this post is a PDF of a study the Woodbury City Council saw in 2011.
More information can be found on Washington County’s award-winning Roundabout U page.
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