But industry observers feel that major problems remain to be ironed out in the technology, which would have to correctly read thousands of number plates every hour before they would be accepted by the driving public.
They also feel that the UK is far behind many other countries such as Norway, Canada and Singapore, which have successfully introduced "road pricing" schemes and then added electronic systems to them.
"It isn't really necessary to have electronic technology to do road pricing," said Stephen Joseph, director of the pressure group Transport 2000. "You can do it with paper permits or toll booths, which is how it was done in Singapore and Norway's bigger cities." Both countries have since made the toll system more or less fully automatic.
The Government will start the latest trial schemes by the end of the year, as part of its continuing attempts to reduce traffic levels and increase use of public transport. The eastern side of the M8 into Edinburgh and the western M62 into Leeds are expected to be chosen as the sites for the tests.
Volunteers taking part in the tests will have "smart cards" with their own chips mounted in the windscreen. These will communicate with roadside and overhead sensors. Drivers will buy electronic tokens which will be loaded onto the smart cards: as they pass the sensors on the way into the city, an amount will automatically be deducted from each card.
If a car's smart card has no remaining tokens, its number plate will be photographed and a bill sent to the owner's address. The amounts charged could vary from pounds 1 to pounds 5, to see how that affected drivers' behaviour.Reuse content