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

Where a roundabout is simple, these are complicated

By Rain Noe - August 9, 2016

in Cars | Urbanism

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:

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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:

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

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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?

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Johan De Man

8 years ago

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I think they forgot the busses, bycicles and pedestrians ... maybe make it even bigger in area :-)

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Mark Thomas

8 years ago

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I think it worth noting that the two scenarios differ by more than just the CFI. For example, there are more lanes in the "with proposed improvements" video, and other differences like larger radius onramps, metering upstream from the CFI, et. al.

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Carl Burdick

8 years ago

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How suburban. I would hate to be a pedestrian or cyclist anywhere near this thing.

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G H

8 years ago

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This seems like a much more complicated and expensive version of a jughandle.
https://en.wikipedia.org/wiki/Jughandle

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- O Studio
  
  G H
  
  8 years ago
  
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  On first glance I agree - it's like a jug handle except it makes the road much wider and adds more traffic lights, making this one intersection that really breaks up the landscape. I would have to better understand the rates of traffic flow through here to appreciate this. Maybe I'll go watch the video on repeat...
  
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