Commuters who share driving duties for their journey to work could be rewarded under new plans to be announced by the government.

Alistair Darling is set to unveil the initiative this week in a bid to tackle congestion and curb pollution.

The idea proposes a dedicated fast lane on motorways for 'high occupancy" vehicles - cars carrying two or more people.

The system is set to be piloted on parts of the M1 and M3.

Initially the scheme will only be run where roads are already being widened or where the hard shoulder is in use. It will only operate at morning rush hour.

The system has been imported from America, where Alistair Darling travelled earlier this year on a fact-finding mission.

Up to three million commuters use the special lanes each day in the United States.

The new system is bound to spark controversy among hard-pressed commuters.

Drivers who use the lanes illegally will be subject to £100 fines.

The government anticipates that commuters may perceive the penalty as another "stealth tax" on motorists.

It has also been noted that some workers, such as nurses on late night shifts, would find it impossible to share their vehicles.

Using cameras to enforce the rules has been deemed impractical, so new police patrols will be employed to do the job.

Stephen Joseph, executive director of Transport 2000, gave a cautious welcome to the proposals, although he was "concerned this isn't just an excuse for road-widening".