How to enforce 3-foot passing safety laws to protect bicyclists

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Twenty-six states and the District of Columbia require that motorists give bicyclists at least 3 feet of space when they pass.

It’s the law.

Device measures distance to passing cars

Device measures distance to passing cars

But one of the big hurdles bike advocates face in pushing for passage of such legislation is enforcement. In state after state, police and legislators say that the 3-foot law is unenforceable.

Now, the Chattanooga Police Department is proving the law is enforceable. A police officer is using ultrasonic technology to detect motorists who violate Tennessee’s 3-foot passing law enacted in 2007.

According to, Officer Rob Simmons can measure the distance of passing cars by using an ultrasonic detector mounted on the handlebars.

Created by Codaxus of Austin, Texas, the device is called the C3FT. It displays the distance of a passing car and sounds an alarm or flashes a light if the vehicle is closer than the pre-set distance. A camera set up next to the unit can create an image of the passing vehicle and the distance displayed on the monitor in the same frame.

As of mid-June, Simmons says that he’s pulled over 17 motorists for passing within 3 feet of his bicycle. He has not issued any citations, but gives the motorists a good talking to. He said most are unaware of the 3-foot law, and his main job right now is public education about the law.

The public education project was undertaken with funding from Friends of Outdoor Chattanooga.

More information about the C3FT distance detector can be found at the company website.

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