Government plans to reduce traffic congestion are doomed to fail because of a widening gap between motoring costs and public transport fares, according to the government's top transport adviser. The central target of the 10-year transport plan - to get people to switch from cars to buses and trains - will be undermined by a 20% fall in the cost of motoring and an equal rise in public transport fares, said Professor David Begg, chairman of the Commission for Integrated Transport.

Transport secretary Alistair Darling, who will address the House of Commons on Wednesday about the transport plan, said it was expected that as the country becomes more prosperous, car ownership and car usage would rise.

"I have said on a number of occasions that as a country we can't build ourselves out of the problems we face.

"We do need to ask ourselves how we can better manage the use of road space as well as putting more money into the railways and buses so that public transport is a reliable alternative," he told BBC's Radio 4 Today show.

Launching a new report which assesses the progress of the 10-year plan, Professor Begg warned: "The government will not be able to achieve a change in the way we travel against these price trends."

Congestion to worsen

The report predicts the government will miss a series of key targets for 2010.

Congestion will continue to worsen, train passenger growth is running at only one tenth of the target rate, and rail punctuality has fallen.

Road charging could be introduced

How ministers defend plan

Mr Darling said existing road space needed to be managed better, new construction was required to deal with bottlenecks and motorways "under severe pressure", and continued investment was needed in public transport.

He also said road pricing, to be introduced for lorries from 2006, "is one of the things I think we need to look at".

"Whether or not it is technically feasible... remains to be seen."

Professor Begg said ministers must show far greater support for a national system of road-user charging, when they publish an update on the 10-year plan next year.

Road charging

The plan assumed 20 English towns and cities would introduce congestion charging or a workplace parking levy by the end of the decade, but only London and Durham have launched schemes, while Nottingham could follow.

Widespread protests against the rising cost of fuel helped blow the government transport plan off course between 2000 and 2002, according to Professor Begg.

Ministers scrapped the 6% escalator on fuel duty, which acted as a fiscal brake on traffic growth.

Cars are becoming cheaper, and road tax has been reduced for less polluting vehicles.

The Strategic Rail Authority announced last month that regulated train fares, such as commuter season tickets in south east England, would rise by 1% above inflation, scrapping a formula which since privatisation has capped increases to less than inflation.

Many unregulated fares - especially long distance tickets at peak times - have risen significantly in real terms.

The government had also become "downright negative" on plans for congestion charging in cities, said Professor Begg.

Even if transport targets look set to be missed, Professor Begg welcomed a big rise in government spending - more than ministers had promised.

He said capital investment in railways had increased from £19 million three years ago, to £1.3 billion this year.

>From the BBC News Service