GOT SAT-NAV? Even if you never received last year’s “must-have Christmas present”, you’ve probably seen them around. They’re the cute little gadgets for your car that talk to military satellites 12,600 miles up, then say things like “Turn left . . . now!” in a calm, friendly voice. But while you see a speaking A-Z with a suction pad, Transport for London has other ideas. It is testing the use of sat-navs for the ultimate congestion charge: in which every journey will be logged and paid for by the mile.

Generally, people don’t like paying for something — road use — that until now has been, with a few exceptions, completely free. Ninety-five per cent of Britons oppose road pricing, suggesting that a commuter is as protective of his right to travel along the A61 unimpeded as an Orangeman marching down the Garvaghy Road. But that’s a mistake. Road pricing has the potential to end traffic jams on our roads, permanently; to make driving a pleasure again. And here’ s why.

First, a thought experiment. What would happen if you tried to buy the street on which you live? Bear with me on this one: a peculiar idea it may be, but the results are interesting. Let’s say that you live on a busy, congested route. Once you had bought your road, you would probably try to reduce the noise of the traffic grinding past by setting up toll booths at either end and charging a hefty fee for any car that wanted to use it.

Now if you simply kept on charging sky-high tolls, the system would not work out so well for you; drivers would get wise and take a different route through the back streets to avoid the charges. Your revenue would dry up. On the other hand, if your toll was low, too many drivers would try to use the road, leading to congestion and not a lot of cash. The best strategy would be to work out a price at which as many drivers as possible passed through your gates without the traffic slowing down. On top of that, you would set a higher price at peak hours, to spread commuting through different times of the day. To keep the punters coming, you’d use most of the money for repairs to stop the road deteriorating.

Of course, all the other roads in the country would be run by capitalist tycoons as well, and they too would be playing the game of trying to charge the optimal amount. No road, therefore, would stay clogged up for long; it would simply raise its prices, diverting enough drivers to other streets or other times of day until traffic started flowing again. And something extraordinary would happen: congestion as we know it would cease to exist.

There are a few problems with this system. First, users need a way to weigh up myriad road prices and adjust their journeys accordingly. Secondly, setting up a toll gate on every tiny road in the country has always seemed fanciful.

Until now, that is. Properly programmed, the sat-nav on your dashboard can handle both problems: simply tell it where you want to go and then compare the prices of different routes. The North Circular, for ten minutes, for a charge of £5, or a 30-minute detour for £1.50: the choice is yours. If the price is too high, you might even use public transport. And once you’ve made your journey, the device in your car can beam its cost up to the satellites, down to a central computer somewhere and send you a monthly bill. The money would go towards the upkeep of the network.

This is not science fiction. In fact, it is almost Government policy, with good reason. Since the mid-1960s, the number of cars on the road has tripled but the size of the network has only grown by 23 per cent, leaving Britain with the most congested roads in Europe. Over the next 30 years, as the number of households doubles, arterial roads are set to fur up completely. Alistair Darling, the Transport Secretary, has called for road pricing nationwide, having commissioned a study that estimated that the system could cut congestion by 40 per cent with only 4 per cent fewer cars on the road.

Unfortunately, Mr Darling’s pace is glacial. A pilot version of the project for lorries has been mothballed. Meanwhile, he wants a cross-party consensus, which could take a while. The Tories are sceptical: the sort of people who drive into London each morning are exactly the swing voters they’re trying to woo, and a commitment to charging them extra isn’t going to help. Mr Darling’s only real action has been to bribe city councils to start their own road-pricing schemes, using whatever technology they like. The likely outcome is a mess of different charges, which will set a national system back years.

Mr Darling tells us that the technology for a national scheme will not be available until 2015. But attitudes are changing faster than that. Once insurance companies start offering cheaper rates for drivers who install satellite navigation, last year’s novelty item will become standard in-car kit. Bernard Grush, who runs a road pricing software company in Toronto, reckons that a fully reliable sat-nav charging system could be only four years away. He even suggests that the gizmos could be used to charge people for parking spaces, doing away with pay-and-display forever.

A bit of oomph is needed. The Government should make its plans concrete by introducing legislation; once political will is there, technology will follow. Sadly, Mr Darling is stuck on amber, and he’s holding the rest of us up. It’s time he listened to that calm, friendly voice inside his head that says: “Move forward . . . now!”

gabriel.rozenberg@thetimes.co.uk

Times Recommends

• It’s the beginning of the affair
• Afghanistan: still a price worth paying
• Heroes of the downtrodden