A lane reserved for vehicles carrying two or more passengers will be tried out on the motorway between junction 7 at St Albans and junction 10 at Luton during peak times.
Work to widen the motorway from three lanes of dual carriageway to four has already been programmed and will start next autumn. The car pool lane should then be operational by 2008.
The DfT hopes the scheme will be relatively self-enforcing. If the trial proves to be successful, it will consider extending the lane to junction 13.
Transport 2000 spokesman Steve Hounsham applauded the scheme as forward thinking.
"This move rewards those who do their bit to reduce the problems brought by traffic," he said.
But Hounsham added that he would not like to see the promise of car-share lanes used as an excuse to widen motorways further. "The ideal solution is to take a lane from an existing motorway and turn it into a car pool lane," he said.
Atholl Noon, director of transport planning at Colin Buchanan and Partners, warned that shared lanes do not see great benefits unless the number of people in each vehicle is increased, which would entail a change in travel behaviour. "The real benefits come when bus companies add more services," said Noon.