[votingprawn]

I reckon an RPi type camera would be perfectly sufficient to estimate speeds, probably to a higher accuracy than you ask.

Edit: a quick search led me to this https://gregtinkers.wordpress.com/2016/03/25/car-speed-detec...

and this https://github.com/pageauc/speed-camera

[criddell]

Wow! That's perfect. Thanks for the links.