It seems Arizona is waking up to a new radar that detects tailgating. This is apparently already popular in Canada, Australia and Hong Kong and is gaining popularity in the US.

I've not heard of these being implemented in the UK just yet (but there are plans), but give it time, and we'll see these babies in full time use in the UK along with all the other cameras (speed, surveillance and number plate recognition) we have already. What's more, the UK will probably automate it, and stick it on top of a pole to save money.