Future governments must accept that a growing economy will produce increases in traffic volume, according to a report by the British Roads Federation.
The pro-roads pressure group said that, between 1963 and 1993, for every 1 per cent growth in gross domestic product there was a 2.5 per cent increase in traffic volume.
The organisation said that the link between economic performance and traffic growth could not be ignored. "The main political parties are pledged to increase living standards and reduce unemployment," said Richard Diment, director of the federation.
"If that is achieved, then it will mean more traffic on our roads than today. We need to plan ahead to cater for this increased demand."
The federation claims that Britain may have more than 31 million cars on the road by 2020 as opposed to the current total of 21 million. They said motorway traffic had tripled since 1975 and household expenditure on motoring had increased by 32 per cent in real terms since 1979-80.
Alarm UK, a pressure group monitoring the Government's road building programme, dismissed the federation's claims as "the last gasp of a dying dinosaur".
"These are extraordinary assertions. They're living in a bygone age. This report is a rapid reaction because they are losing the transport debate - the Government is no longer trying to build enough roads to cater for traffic growth," John Stewart, of Alarm UK, said.
He added that the Government was looking at other ways of meeting the expected growth in transport needs, and the recent moves to increase provision for cyclists and walkers in cities proved an integrated transport policy was on the agenda.