This week we answer a pretty common CoMo question: what's with all the roundabouts in Columbia?

There are 21 roundabouts in Columbia. For a lot of Columbia drivers, roundabouts are weird and unfamiliar. But is it unusual? We discovered it's not. Columbia is a growing town with a lot of construction, so that's one reason why you'll see a lot of them. But believe it or not, roundabouts are the big new thing in traffic engineering. They're popping up in a lot of other cities, too, and they're poised to become extremely common.

The history of roundabouts is more interesting than you think. It started in the early 1900s--essentially the very beginning of traffic. Automobiles were still sharing the road with horses then, but the need for streets built specifically for cars was a growing concern. One William Phelps Eno designed a lot of our early road infrastructure like the stop sign, the cross walk, the taxi stand and the traffic circle. He built Columbus Circle in New York, a pretty famous intersection as far as intersections go.

The "traffic circle" at this time was a different beast compared to the modern roundabout. The traffic circle was big, fast, and confusing. Sometimes entering traffic had the right of way, meaning cars would zip into the circle without yielding. There were a lot of accidents and eventually we gave it up. By the 1950s, a lot of existing traffic circles got stop signs and lights to reduce crashes. Building new traffic circles was pretty much off the table.

But our friends in the UK continued to build these things and eventually settled on a new and improved design. By 1975, they had designed what we now call the modern roundabout. These had two main differences: First, instead of approaching the circle head on, a divider would steer you to the right before you enter the circle. Second, there's a yield sign instead of a stop sign or a light. These sound like really small changes, but they made all the difference. Research has shown that they almost completely eliminate "t-bone" collisions--the kind where an oncoming car runs directly into your side. That's pretty much the most dangerous way to get hit. Compared to a stop with signals, roundabouts have 78% fewer accidents that involve injuries or death.

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