Well, he's hearing how fast you're going, anyway. According to a report in New Scientist, law enforcement agencies may soon have a new tool for catching speeders: hidden roadside microphones.
The speed-sensing system is currently being developed by the University of Tennessee and the Battelle Institute in Oak Ridge, Tenn, according to patent application documents uncovered by New Scientist. The concept is that microphones mounted in road signs, guard rails and other roadside locations can record the sound of passing vehicles, filtering the recording to isolate only the sound of the vehicle's engine. By measuring the Doppled shift (the change in pitch as the vehicle drives by) of the engine noise, proponents claim they can calculate vehicle speed. They also claim they can measure the engine's actual rpm and compare the sound of the reciprocating pistons against a catalogue of known acoustic signatures. Theoretically, this info could be used to determine if a truck is overloaded, by analyzing recordings from microphones on a slope of known incline and comparing the changes in engine speed to road speed.
Get ready for aftermarket sound generators and assorted stealth mufflers.
And the first few court cases should be mighty interesting. "But your Honor, I wasn't driving that fast; I was merely playing some recorded engine noises really loudly on my stereo." —Don Chaikin
The patent application for an acoustic speed sensor.
Patent application image of the system in action.
The bells and whistles of the system, we think.
The circuit schematic of (a piece of?) the device looks strangely similar to the cubicle layout of our soon-to-be-former office.