A dedicated motorway lane for drivers with passengers is to be launched in the UK - despite warnings from America that such schemes are often under-used and can worsen traffic jams.

The transport secretary, Alistair Darling, yesterday announced that a one-mile stretch of road in Yorkshire joining the M606 and the M62 will be widened to include a £2.5m car sharing lane to open by the end of next year.

The pilot will be followed in 2008 by a similar lane on the M1 between Watford and Luton. If successful the scheme will be extended to many other motorways across the country.

Cars carrying two or more people will be allowed to use the lanes, which will be enforced by police patrols. Any lone drivers caught on them will face a fine.

Councils in Leeds and Bristol have already tested the idea on local roads. On one road in Leeds it raised the average car occupancy from 1.35 to 1.5 passengers.

However, motoring organisations are sceptical about whether motorway drivers can be persuaded to allow an extra person to share their space - a reluctance dubbed "nimf-ism" or "not in my front seat".

Americans have developed elaborate ways to get around restrictions - including using blow-up dolls to fool enforcement cameras and hiring university undergraduates to occupy passenger seats. Some states allow lone drivers to use them if they pay a toll - a possibility being considered by ministers for the M6 between Birmingham and Manchester.

The RAC Foundation believes many drivers value lone control of their stereo systems and air conditioning so much that the prospect of dodging traffic jams will not motivate many to carry a passenger.

Edmund King, the foundation's executive director, pointed to a study by the University of California which found that high occupancy lanes were counter-productive. "Let's have a pilot, let's look at it, let's see if it works - but one has to question whether a one-mile stretch is enough of an incentive for people to change their commuting practices," said Mr King.

The American study found that relatively few people used high occupancy lanes - and those who did were often held up by slow moving "snail" drivers.

In Britain the Highways Agency hopes that car sharing will lead to a 5% to 10% reduction in vehicles on roads.

But the AA Motoring Trust's head of traffic policy, Paul Watters, said pooling would only work if car parks were provided where commuters could swap vehicles. "We do need to start looking at proper infrastructure to encourage car sharing," he said. "There's a risk that these new lanes will stay fairly idle and won't be properly used."