By Tom Symonds BBC transport correspondent

The government's new plan for a toll motorway was like a sudden switch of lanes by a driver trying to make a slip road he was in danger of sailing past.

Paying for new roads by charging motorists was something the Conservatives did - until Labour realised it was too handy an opportunity to miss.

The M6 Toll has not provoked a backlash from car drivers

The announcement of a consultation into the idea of a new M6 Expressway between Birmingham and Manchester was certainly a surprise.

When Britain's first toll motorway - the M6 Toll - opened last December the Transport Minister Alistair Darling was happy to cut the ribbon, but he wasn't falling over himself to offer more of the same.

But when the M6 Toll turned out to be relatively successful, that finally convinced the government to plan a second toll road.

It seemed to be popular with car drivers, if not lorry companies, which have to pay much higher charges.

Crucially there doesn't appear to have been a backlash from those drivers stuck on the old M6 and not prepared to stump up the money - they're enjoying a 10% drop in traffic.

Relatively unpopulated

The M6 Expressway, built alongside the current motorway, offers two main advantages to the government.

By not simply widening the existing road, M6 users are spared a decade of road cones.

And by paying for the new road through tolls, the government frees up money for public transport - or possibly more roads.

There is a chance the government will take the same approach on other major motorways.

Politically, charging for brand new roads is easier to sell than asking drivers to pay to use those that are already there Tom Symonds

The problem is that the M6 north of Birmingham runs through a relatively unpopulated part of the country.

Adding lanes to the M1 through Luton, for example, would require a serious battle over planning and large amounts of demolition.

So what does the new enthusiasm for toll booths say about the future of roads?

It does suggest the government believes the idea of paying to drive is starting to be accepted by motorists.

Politically, charging for brand new roads is easier to sell than asking drivers to pay to use those that are already there.

Radical proposals

But the concept that motorists should be charged when they use roads at peak times is gaining ground.

The London Congestion Charge has led to a drop in traffic of around 20% - again, there has been no noticeable rebellion from drivers.

More radical proposals could be on the way.

Not long ago Mr Darling personally chaired a seminar to look at the possibilities of charging drivers, albeit as part of a national scheme on the current road network. A report to be published in the next few weeks will explore the idea further.

Traffic on the old M6 has dropped by 10% since the toll road opened

The problem with toll booths as a way of collecting the money is that they hold up the traffic rather than speeding it up.

Instead the government could use satellite navigation technology to detect which roads a car is using, and bill the driver accordingly.

But this would involve fitting every vehicle in the country with a satellite receiver, not an easy task.

Ministers continue to rule out any nationwide tolling scheme for at least the next eight years.

The government is under pressure from two directions - anti-roads campaigners believe building new roads simply stimulates more people to drive, as well as damaging the environment.

Snails' pace

Pro-roads campaigners believe not building new roads will damage the economy as goods lorries and employees sit in traffic.

Toll motorways are starting to seem like a compromise between the two. The tolls provide the money to build the roads, but it's hoped they also dissuade drivers from making unnecessary journeys.

Expect all these decisions, and the road-building itself, to move at a snail's pace.

The new M6 Toll road won't be finished until the back end of the next decade. National road-charging is probably a decade away.

The problem is that drivers are sitting in jams now, and want to get moving again.