Motorists will be offered incentives to take part in road-pricing experiments, under government plans to rescue its policy of reducing congestion by charging vehicles by the mile.

Rather than forcing drivers to install a black box, to track their cars’ movements, ministers hope to encourage volunteers by making the system financially attractive.

The Government was taken by surprise by the strength of feeling against road pricing in the petition opposing the idea on the Downing Street website. It attracted 1.8 million signatures, compared with 5,000 for a petition supporting road pricing.

The Department for Transport is developing an approach where drivers will be offered a choice: carry on paying motoring taxes or switch to a road-pricing meter in the car that could save money.

Drivers could be offered a discount on fuel duty in return for agreeing to pay a distance-based charge, which would vary according to the level of congestion. DfT officials are studying an American trial in Oregon in which drivers who agree to pay a mileage charge have duty deducted from fuel bills.

The department hopes to test the voluntary approach in regional pilot schemes due to be announced this year. Manchester, Birmingham and Cambridge are being considered for the experiments.

The hope is that positive reports from volunteers will help to silence suspicions about the concept, including concerns that the black box will be used to spy on drivers’ movements and to raise the overall amount paid in motoring taxes.

Ministers have promised repeatedly that neither of these things will happen but the size of the petition suggests that many drivers do not believe them.

Under the new approach, drivers would be encouraged to see the black box as a useful tool, not an intrusive tracking device. The box, which would use satellite positioning and a digital map to record the vehicle’s movements, would act like a taxi meter. Drivers would be able to see the true cost of their journey mounting up as they sat behind the wheel and might decide to travel at a cheaper time, by a cheaper route or even on public transport. At present, motoring taxes are almost invisible to drivers because road tax is paid annually and fuel tax is collected automatically at the filling station.

The RAC Foundation supports the voluntary approach but believes that the Government should offer participants a whole package of benefits. It has developed a concept called “UK Drive Time”, which would involve installing a black box capable not just of calculating the distance charge but also of giving advice to the driver about congestion and offering faster alternative routes.

The system could also allow the driver to pay less for insurance. Norwich Union already offers a “pay-as-you-drive” policy under which drivers pay less if they avoid driving late at night and in the morning peak, when most crashes occur.

Edmund King, the foundation’s director, said: “It would be political suicide to force road pricing on drivers. They need to be tempted to opt in.” David Begg, the Government’s former transport adviser, said that ministers should learn from the introduction of the Oyster travel card in London. “No one was forced to get an Oyster card but the incentives were gradually increased and now more than ten million people have one,” he said.

An American road pricing experiment in Seattle found that almost 80 per cent of volunteers made fewer car journeys on congested roads when offered a financial reward.

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