A HIDDEN trap that detects how fast vehicles are going just by listening to them as they pass could catch speeding drivers unawares.
The system, being developed by the University of Tennessee and the Battelle Institute in Oak Ridge, uses microphones hidden by the roadside to measure the speed of passing vehicles. It does not emit telltale radiation, unlike radar or laser-based devices, so it cannot be picked up by dashboard detectors.
Once the microphones have detected and recorded the sound of a passing vehicle, digital filtering removes background noise to leave only the sound of the engine. Software then calculates the vehicle's speed by measuring the engine sound's Doppler shift - the change in a sound's pitch as its source moves past an observer.
The system, revealed by recently filed patents, has been developed with funding from the US Department of Energy. The microphones could easily be hidden in ...
20:00 03 July 2008
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