Mr MacGregor has asked officials in his department to accelerate a study next month into the feasibility of road pricing with a survey of commuters who drive their cars into London.
His predecessors, including Cecil Parkinson, considered road pricing but avoided making any commitments before the general election, because it was too controversial.
But Mr MacGregor has privately told colleagues that congestion in London and other main cities will have to be tackled and road pricing appears inevitable.
Commuters will be asked how much they would have to be charged before they would be prepared to alter their travelling times, or leave the car at home and travel by train.
Although the Government has been looking into the feasibility of road pricing for some time, the study marks a clear shift of policy by giving it a higher priority. Mr MacGregor has asked for the report by the end of the year.
The Government, under Margaret (now Baroness) Thatcher was wary of road pricing because it was feared it would penalise Tory voters in the London suburbs and the Home Counties.
Mr MacGregor, one of the Conservative Party's key political strategists in the run-up to the election, believes that there may be more votes to be gained from easing the road congestion, than to be lost from road pricing.
Traffic speeds in peak hours in London have fallen to little more than 10 miles an hour and ministers believe that, having prepared the ground for toll roads, commuters may now be more prepared to accept road pricing at peak hours.
Some key members of John Smith's Shadow Cabinet have opposed road pricing because it would act as a regressive tax, penalising hardest those on low incomes. It was also argued that firms would pay the charges for their top employees, creating another perk for executives and leaving other members of the public at a disadvantage.
But John Prescott, Labour's transport spokesman, has been more sympathetic, seeing road pricing as part of an integrated transport policy, provided it was coupled with improved rail travel.
Unless Mr MacGregor was able to couple road pricing with firm promises of improvements in rail services into the capital, it could backfire.
The technology exists for metering cars entering cities. This could avoid further delays at toll booths on main commuter routes, but, according to some estimates, it could cost pounds 100m to implement. It may prove impossible to stop road users dodging the charges by using side roads into the city.
Mr MacGregor has shown he is willing to take unpopular decisions, such as the widening of the M25 into a multi-lane highway to ease the most congested sections. And he is prepared to face up to the wrath of local environmental groups to see the scheme launched.