New type of speed camera...

[tmov81]

Are you a scientist?

I only ask because I think you'd need to be to make that call... I'm not a scientist myself, so I can't think of a reason why sound-based speed-detection is any less legitimate than radar.

Perhaps the two could be used together to improve the reliability of the readings they provide?

yes i am...

I am currently doing my Ph.D. in the measurement reliability and validity of
piezo-electric transducers where low level force/moments are registered and the extent to which trial protocol, sample rate, filtering protocol and environmental noise cause the recorded signal to vary from the actual performance...

i hope that answers your question

radar/lidar is shooting multiple pulses at a vehicle and calculating the variation in time for the pulse to bounce back. yes it can be inaccurate, but that is mostly down to if the operator does not use it properly.

attempting to pick up the tone/pitch of the exhaust note is a waste of time. it probably could be done, but it will always be less effective than radar/lidar, and it will be subjected to so many more extraneous variables. You cannot simply filter out the exhaust note of other vehicles. for example two stock 1.8L astras cruising side by side. the exhaust note will be fairly similar frequency/amplitude. how do you isolate the exhaust note from one vehicle? more importantly how do you set it up to be automatically operated?
what happens if you have a motorbike coming in the opposite direction... it will sound like you are hammering it as you move away from the sensors... there are just too many uncontrollable factors.

attempting to identify changes in the exhaust note as it drives away is a lot more complicated than shooting a laser beam at the car. it could possibly work, but it is a waste of time... i mean if anyone can come up with suggestions as to where radar/lidar could not be used but sound based analysis could be used... but i for the life of me cannot think of any reason why people would waste time and money doing this other than so they can say they can... i mean its like saying i drove from melbourne to sydney via adelaide... yeah you might be the first person to do it... but who cares... you can drive directly from melb to syd and it is quicker, cheaper and makes your trip less prone to problems.

[pred8r]

I will say yes it would work, but the accuracy could be questionable.
I live on a long straight and someomes late at night ive heard cars(?) go past QUICK (100kmh+ easy) and all you hear is the tyres on the road.

if they measured the sound at say 1m apart then they will know how fast you are going. Given distance and time taken would give them your speed exactly.

The Amphometers were one of the most accurate way of catching speeders, except you could see the straps.
They use something similar on the western ring rd in melbourne (uses 2 cameras and in-ground straps to do it).