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Alternative Road Design: Here’s How a Continuous Flow Intersection Works

Driving in Manhattan can be a nightmare, but there’s one thing about it I always appreciated: Because most of the streets are one-way, there are few instances where you need to make a left turn against oncoming traffic.

That type of left turn has traditionally been a pain point for planners and motorists alike. It’s inherently dangerous for incautious motorists, and annoying for those stuck waiting behind overly cautious motorists. Observing this, in the 1980s Francisco Mier, a businessman from Mexico, and Belisario Romo, his engineer partner designed a new type of intersection: The CFI, or Continuous Flow Intersection.

The word “continuous” is a bit misleading, because it’s not like a roundabout, where cars are always in motion. Here’s how a CFI works:

To date, less than two dozen of the intersections have been created in America, though Civil + Structural Engineer Magazine reports that Mexico has had at least 40 CFIs “for decades." 

The U.S. state of Virginia is the latest to take the plunge—that’s their video up above_and they mention that "Federal studies show crash rates are reduced by almost 25% at intersections where a CFI has been installed.”

On top of reducing the accident rate, CFIs provide better traffic flow. Here is the Virginia Department of Transportation’s computer simulation, showing a fixed number of cars at the intersection in question, with a CFI format:

And here’s what happens with the same number of cars at that intersection without adding the CFI modification:

Assuming the simulations are accurate, presumably the improved flow of traffic is worth the added cost (more asphalt, more signals) required to build a CFI. The bill for this one is $59.8 million, and it should be finished by May of 2018. But as you can see by the video, they’re doing this with the future (using 2038 as a benchmark) in mind. You reckon we’ll have flying cars by then?

http://www.core77.com/posts/55299/Alternative-Road-Design-Heres-How-a-Continuous-Flow-Intersection-Works