Caught by the sound of your speeding engine!

[William]

New Scientist article I came across today.

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.

New Scientist Article Link

 

[William]

just pull it out of gear once your satisfied your going fast enough

I believe doppler shift would negate this also, it is looking for a change in pitch of any sound so I guess tyre noise would be the best thing to look for.



Doppler shift for retards:

Spitfire goes past at an airshow, you get the sound:

MEEEEEEEEEEEEEEOOOOOOOOOOOOOOWWWWW!

You determind speed by measuring the distance of the sound and the time it took to change through a pitch range and somthing to do with the speed of light resulting in a speed estimate.

Using this hideous bunch of maths:

http://en.wikipedia.org/wiki/Doppler_effect

 

[William]

I am guessing whoever is developing it has thought of all this, anyway you are travelling so fast over a unit which is at most about 2 feet square then any variation in pitch you make wont work. I doubt it will be implemented, it would be far cheaper just to camo up the exsisting cameras, I don't know why they havn't already.