[robben1234]

>The trouble is, what speed is wrong?

I don't really agree that this is the "trouble". Any competent transit-related professional knows what type of driving is wrong. Even American cops know [0] that in terms of traffic the key thing is to not impede traffic and target dangerous driving.

However, hunting school zone speeders, left lane hoggers and traffic weavers will never generate as much revenue as using an automatic machine that points at cars going faster than arbitrary number.

[0] - https://www.youtube.com/watch?v=yn6C6ZkBdb0