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STUDY: 2-lane roundabouts cause increase in crashes

Posted: 11:22 PM, Jul 10, 2017
Updated: 2017-07-10 23:22:08-04
STUDY: 2-lane roundabouts cause increase in crashes

They’re designed to reduce crashes and delays but an Arizona State University study found some roundabouts, or traffic circles, have had the opposite effect.

The study found single-lane roundabouts cut accidents by 18 percent and decrease injuries by 44 percent.

But two-lane roundabouts yielded different results: While injuries also dropped, the crash rate increased by more than 60 percent, though the crashes were less severe.

The Arizona State professor who ran the study, Michael Mamlouk, looked at data from 17 of Arizona’s approximately 80 roundabout sites before and after they were constructed.

He said the results were surprising, and he thinks he knows why.

“People are not familiar with how to use [roundabouts]. That’s the main thing – they don’t know which lane to use,” he said.

While the study was commissioned in Arizona, the results could apply to some of Indiana's roundabouts, namely several of the two-lane roundabouts among the 100 in Carmel. 

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While a traditional intersection has 32 vehicle-to-vehicle contact points, a roundabout has eight. In the right circumstance, they can be extremely effective, Mamlouk said.

So, how should you drive in a roundabout? Here are some guidelines:

1.     Never merge. The right of way is observed at the yield sign. Motorists already in the roundabout have the right of way. You must slow down or stop to yield to traffic approaching from the left. Wait for a gap in traffic, then carefully proceed into the roundabout.

2. Go SLOW:
Slow down to 15-25 mph when entering.
Let vehicles already circulating go ahead.
Obey all one-way signs.
Watch for pedestrians, bicyclists, emergency vehicles and large vehicles.

For multiple-lane usage, follow these guidelines depending on traffic patterns:

For right-hand turns, travel in the right-hand lane and use your turn signal.
For left-hand turns, travel in the left-hand lane and use your turn signal.
For continuing forward, remain in the same lane you entered.
For missed exits, circle around the roundabout again.