Charging will be needed on about 10% of the road network to stop traffic congestion worsening, a report on motoring warned today.

The only alternative to charging would be a huge increase in road building, according to a report from the RAC's campaigning arm, the RAC Foundation, entitled Motoring Towards 2050.

Motoring groups oppose congestion charging, but the foundation said it was convinced by its report's findings "that in the future charging will be required".

More roads, better public transport, longer-term local transport planning and new motoring taxes would all be needed to avoid future gridlock, the foundation found.

In a foreword to the report, the prime minister, Tony Blair, said that while it did not represent government policy, it was "a well-argued and interesting contribution to the debate".

Testing the findings of the report on 500 drivers, a survey showed:

· 76% would find road tolls acceptable if there were equivalent reductions in petrol prices;

· 73% would find tolls acceptable if there were an equivalent reduction in road tax disc fees;

· 71% find tolls acceptable as a package of better roads, public transport and traffic management;

· 65% find tolls acceptable if there are equivalent reductions in public transport fares;

· 51% want the money from tolls spent on better roads and road maintenance.

If there were no constraints, demand for car travel could be 50% higher by 2031, the document warned, and transport noise was likely to worsen unless technical solutions to improve both vehicles and noise were speeded up.

Improvements to public transport were needed but would not solve congestion problems on their own, it said, but advances in vehicle technology would end the environmental case for preferring rail to road.

In his foreword, Mr Blair said meeting the needs of motorists whilst fulfilling the responsibility to protect the environment was "one of the biggest challenges faced by any government".

"The RAC Foundation first suggested an independent inquiry into motoring issues in October 2000," he said. "In replying, I said that we would welcome a report bringing greater clarity and understanding to the issues and choices. Eighteen months on, this report more than meets that challenge."

Hydrogen powered cars by 2050

By 2050, the report predicted, it was likely that a fuel cell, using compressed hydrogen gas, would become the main form of propulsion.

The government must also ensure that road charging was part of a fair deal and must not "rip off" motorists, it advised.

The RAC Foundation's chairman Sir Christopher Foster said: "The report shows that we need a package of measures to get us out of this transport mess.

"Our independent steering committee has consulted with hundreds of individuals, organisations and politicians before coming to our conclusions. The good news is that technology will clean up the car. The bad news is that congestion will get worse without radical action."

He added: "We know what the radical action needs to be. The urgency is to get on with it. Government must decide on the exact balance of measures needed, but we concluded that unless we saw a massive increase in road building, road charging will be needed."

Mr Foster said that charging must be "fair and transparent" and linked to improved transport infrastructure, both road and public transport, and reduced fuel duty.

He added: "Many may be surprised that a motoring group has opted for charging but our report shows that the alternatives are worse."

Without charging there would be increased congestion and possibly unpalatable and probably ineffective efforts to curb car ownership, he warned.

Government: no plans for tolls yet

Transport minister John Spellar said the government was not currently planning to extend the use of tolls. He told BBC Radio 4's Today programme: "We have certainly not made any decisions on that or got any policy on that at the moment. We are looking at the moment, under the 10-year plan, at redressing the very considerable under investment right the way across our transport network."

Environmental organisation Transport 2000 welcomed the RAC Foundation's support for road charging. Director Stephen Joseph said: "Even motoring organisations now believe road charging should happen. The nervousness shown by the government over it is unfounded."