A vision of the future for Britain's drivers: you get into your car, set off on your journey, and the charging meter on your dashboard flashes up the price of the trip.
It's rush-hour so you're paying more, and you want to use the motorway, so that's extra too.
The total racks up as you drive - and when you arrive at your destination, with a bleep your credit card is charged.
It sounds like science fiction. But it's more likely than not this system will be introduced one day.
Charging could cut congestion by 50%
Despite the worries of some newspapers and motoring organisations, the government still hasn't adopted Road User Charging as its policy for tackling growing levels of congestion.
But the Transport Secretary Alistair Darling is now starting to say there's probably no other option.
The first concrete proposal for a national congestion charge came in February last year when the BBC revealed detailed blueprints for a satellite-based system, drawn up by government think-tank, the Commission for Integrated Transport.
Its report suggested every car should be fitted with a Global Positioning System (GPS), which measures its distance from three or more satellites, and using triangulation, can pinpoint the position of a car within five or 10 metres.
Each vehicle would transmit its location back to a central computer, probably via the mobile phone network.
Different charges would be set, depending on which roads the driver uses and the time of day.
The bit the government likes is that it could cost more to use congested routes, during the rush-hour.
Congestion could be cut
The Commission for Integrated Transport said introducing the system could lead to a 50% cut in congestion, as drivers avoid busier times of the day, choose quieter routes, or, most importantly, switch to public transport.
London's congestion charge has cut journey times
But crucially the commission said overall, drivers should not have to pay more to use the roads.
The report suggested fuel tax should be reduced, along with the price of the tax disc, to be replaced by the congestion charge.
Since that report, Ken Livingstone's London congestion charge has been launched - and there are now 15-20% fewer cars on central London's streets.
Mr Livingstone is still in office, and hoping to win the next election for London Mayor because of the charge - rather than despite it.
So now the government is more willing to talk positively about the proposal.
Alistair Darling isn't going as far as saying yes to road charges, but he does believe it should be seriously considered.
If you turn your mind against [road charges] from the start then you are extremely foolish
"If you turn your mind against it from the start," he said, "then you are extremely foolish."
The government is to get a trial run at the proposal. In 2006 a satellite-based charging system for lorries will be introduced.
British hauliers will get a reduction on their tax disc, and shouldn't have to pay too much more, but foreign lorries will foot the bill.
As for the rest of us, the government has ruled out introducing charges this decade.
In the meantime, ministers are talking about new measures such as staggering school opening times, to ease the pressure on the roads.
One in five cars during the morning rush-hour are thought to be driven by parents taking their children to school.
Even if the government did decide to go ahead with charges, it would probably take longer than a decade to come up with a system that works, pass the legislation, and fit every car in Britain with GPS.
There would be a lot of opposition to the scheme, not least from civil liberties groups, worried that a government computer could contain details of millions of car journeys.
In the end, any government that introduces charging will have to convince motorists of one thing: that the hassle and expense of road charges are more than outweighed by the benefits of quicker journeys.