The experiment, backed by the Department of Transport and the European Community, involves a system of roadside beacons, with 'smart cards' and a reader being fitted into the car. As the car enters the central area, its meter is turned on by a roadside beacon. If its speed falls below a certain level, units are automatically deducted from the smart card.
Professor Peter Hills, head of the development team, said: 'You would charge up the smart card at a service station . . . there would be a machine to do it.'
The system is being tested in Cambridge as part of a Europe-wide initiative to assess and develop the equipment that would be needed for a variety of road-pricing methods. However, Mike Sharpe, Cambridgeshire's director of transportation, said it was unlikely that any full-scale scheme would be operating before the end of the century: 'The hurdles to overcome are not technological but political. There has to be a full public debate and acceptance and it would need new legislation.'
The point was underlined yesterday morning on the local radio station when the owner of McKay's ironmongers in the middle of town warned that he would have to move his business out of town if the scheme was introduced.
Professor Hills thought that several European cities might be operating the scheme before the end of the century.
The experiment is part of a wider, three-year government study into road pricing and transport ministers have recently been more bullish about the possibility of some form being introduced in Britain. The equipment being tested in Cambridge was developed by a team from Newcastle upon Tyne University, and involves only three cars and two beacons.
Yesterday, the pitfalls were all too apparent. A red Ford Escort fitted with the onboard equipment, which included a keypad and electronic display plugged into the car's cigarette lighter, failed to function. A Cavalier was called up but again there was trouble. The machine interpreted efforts to operate the equipment as an attempt to defraud it. 'Violation - card misused. Vehicle Enforced,' the machine responded.