You don't even really need a black box, just a traffic camera that can read your license plate, like a red light camera, maybe combined with a radar gun. Just a

You don't even really need a black box, just a traffic camera that can read your license plate, like a red light camera, maybe combined with a radar gun. Just a camera and some basic physics could probably do it (distance / time = velocity). Once the municipalities start hurting for money even more I bet we'll see this, along with automatic parking citations using cameras.