Britain's busiest motorways are to get special lanes for vehicles carrying more than one person under a government trial, although there were warnings yesterday that drivers may be loath to share their cars.
Alistair Darling, the transport secretary, is to announce four possible sites this week for a pilot of a US-style system intended to crack congestion.
Among the proposals is that a new lane soon to be built on the M1 could be reserved for cars carrying two or more people during the morning rush-hour.
A Department for Transport spokesman said: "It's an idea which has been used very widely in the States. It's to stop the motorways being clogged up by cars only used by one driver."
But the RAC Foundation yesterday suggested that Britain's roads may be unsuitable for car sharing because journey patterns are too diverse, with homes and workplaces spread over a broad area and commuters prepared to drive long distances.
Its director, Edmund King, said American schemes worked best on routes between big residential settlements and concentrated commercial zones - which are rare in Britain.
He added that a car-sharing trial sponsored by the RAC in Edinburgh had encountered a "nimf" attitude - "not in my front seat".
"People in Britain are reluctant to share their own space," said Mr King. "They want to play the radio loudly or pick their noses. They don't want somebody else in the car."
Highways around Washington and Los Angeles have had high-occupancy lanes since the 1970s. In some cases, lone drivers without passengers can pay a toll to use them.
In Britain, local authorities in Leeds and Gloucester already have a few miles of high-occupancy lanes on local roads. They are patrolled by the police because cameras are unable to detect accurately how many people are in a car.
There have been a handful of complaints. One elderly woman in Gloucestershire objected to being stopped when she had a child strapped in the back of the car, who had gone unnoticed by traffic police.
Mr Darling is thought to have an open mind on the possibility of charging lone motorists to use the lanes. He is due to publish a feasibility study next week on national road charging, which examines how satellite technology could be used in 10 years' time to charge drivers for every journey they take.
A charging scheme is due to be introduced in 2008 for lorry drivers, which is likely to cost around 20p a mile. Freight leaders expressed doubt yesterday about high-occupancy lanes which could put toll-paying lorries at a disadvantage.
Richard Turner, chief executive of the Freight Transport Association, said: "High-occupancy lanes might become more practical if they could be used by commercial vehicles."
The Confederation of British Industry estimates that congestion costs the economy about £20bn annually.
Police patrolling the new lanes will have to be alert for motorists bending the rules. In California, drivers have placed dummies on their passenger seats and even hired students to enable them to use high-occupancy lanes.
· The government will be urged to do more to encourage bus patronage today in a report by the Commission for Integrated Transport. The study urges the use of congestion charges in towns and cities to pay for improvements to bus services.
