Or just an e-plate
RFID tag in an e-plate with a tamper proof design (plate shatters on removal) RFID readers from 100m up to 300mph and ANPR gives a system that can see any car without an e-plate amongst those who do, work out the very simple equation of time/distance for speeding offences, provide all data in an accident investigation, track untaxed vehicles, uninsured vehicles, stolen vehicles. Perhaps a charge for insurance agencies asking for data, tracking for company cars all kinds of data. Real time traffic flow monitoring by every single vehicle and average speed, accidents maybe even diversion/road closure/accident info sent to all vehicles in range?
Around £60 ? for the plate and less £ for readers in already expensive street furniture such as streetlamps say 1% of cost. Calw back money from insurance agencies and firms wanting to monitor their fleet, traffic info down to each induvidual vehicle and t's speed (algorythum (sic) to work out where jams are based over empty road trials and a simple comparison bult over months of 24hr data including rush hours).
Charging for road usage, alerts for the police over any vehicle without a number plate (obvious) any vehicle trying to hide in a flock through ANPR is spotted as a flase read, or simple induction loops to check number of vehicles vs number of eplates and send out a car to to count and remove those who are legal (as in all legal with tax, insurance, mot, no warrents, tickets or speeding).
Wow, a rant and a half, i should say e-plates with RFID readers built into every lampost at manufacture and the existing ANPR system extended to catch the low percentage who are breaking the law would cover itself through fines, data sales, and road tax alone. Also traffic modelling could reduce the UK carbon footprint with that much data.