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The Case for More Traffic Roundabouts

Stashed in: Cars!, Math!, Design, Mathy, Freakonomics

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We really don't like roundabouts in America. 

Roundabouts Are Safer

According to data from the International Road Traffic Accident Database, some six million traffic accidents occur each year in the U.S.; of these, 40% happen in intersections.

Statistically speaking, intersections (both 4-way, and t-shaped) are deadly places: Based ondata collected between 1998 and 2007, 21.5% of all traffic-related deaths, and 44.8% of alltraffic-related injuries occur in intersections. On average, 9,000 people die and another 767,000 are injured in intersection collisions every year in the U.S.

Intersections may be convenient and familiar for drivers, but their inherent design allows for a proliferation of high-speed, high-impact crashes. Utilizing simple physics, roundabouts significantly mitigate these risks. Tom Vanderbilt, author of Traffic: Why We Drive the Way We Do, explains why:

“Roundabouts are typically built using what's called ‘negative superelevation,’ meaning that water flows away from the center and also that the road slopes against the direction of a driver's turn. As a result, any crashes in a roundabout take place at lower speeds and are thus less likely to be fatal...They also eliminate the left turn against oncoming traffic — itself one of the main reasons for intersection danger — as well as the prospect of  vehicles running a red light or speeding up as they approach an intersection to ‘beat the light."

Roundabouts reduce crashes by the very nature of their geometry. While traditional four-way intersections have 32 possible collision conflict points, roundabouts have only 8:


Collision conflict points: intersections vs. roundabouts; via The Federal Highway Administration

Interestingly, our fear of roundabouts also plays a role in making them safer: since they are unfamiliar to us, we are weary about entering them and are extra cautious. On the other hand, we’re accustomed to intersections, and more likely to take risks when driving through them.

They may be safer,but they're unenjoyable to drive through. 

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