3 feet or else: Chattanooga police use ultrasound technology to enforce law for cyclist safety | Local News | Times Free Press

"BSMART (Bicyclist and Safe Monitoring Applied Radar Technology), made by Austin, Texas-based Codaxus, LLC, bounces ultrasonic waves off passing vehicles and calculates for distance.

It's a brand-new technology, developed by friends of Chattanooga Police Chief Fred Fletcher. Chattanooga is the first city in the country, and possibly the world, using it."