The Government's roads programme faces a no-win situation, a transport expert has suggested to MPs.
University College London emeritus professor of transport policy Phil Goodwin told the House of Commons Transport Committee that there is a "paradox at the heart" of the plans.
Ministers want to unclog the highways to get the country moving and prevent time and money-costing delays.
The paradox is that the planned roads programme is "not big enough to make an improvement" if traffic rates rise, the transport policy professor warned.
Conversely, if traffic congestion drops then the planned schedule is "too big to justify the cost", Prof Goodwin said.
The Department for Transport forecasts a jump in car traffic levels, and the professor told the committee that there are six vital words missing from the Government's roads White Paper: "This programme will reduce congestion naturally."
Prof Goodwin said other specialists "seriously dispute" the increase in traffic rates.
He said that road pricing on motorways and A roads is the best solution for coping with congestion, but added that this is "unlikely to be politically unacceptable".
Pete Williams, head of external affairs for the RAC, said: "This highlights one of the most problematic issues for those involved with long-term planning of our road infrastructure, however, it is right to commit to the programme of investment suggested in the Action for Roads paper.
"Nine in 10 journeys in this country are made by road and, following decades of projects that have not been handled properly, we are now positioned 24th in the world for our road network.
"It is now a priority that this significant investment is carried out to improve travel in the UK for generations to come."
Copyright © Press Association 2013