ANPR (Automatic number plate recognition) cameras in use in the UK (and probably many other places) already do this using computer text-recognition to scan every plate that goes past the camera, and then records the date and time and a video clip into in a database. The police can go back later, type in a plate number, and it will show them every time that car went past any ANPR-enabled camera.
Computer vision is good enough now (in a limited/uniform context like license plates) that RFID isn't really necessary. All it takes it a radar gun, a camera, and some fancy software.
Also, passive RFID (the kind found in smart cards) only has a range of about 3 feet, so it would have to be a battery-powered or car-powered active RFID tag (300 foot range), but then you get into issues of drivers being able to turn it off at will.