We have to act today or it's jam tomorrow

ROAD pricing is very much back in the public debate. So what is road pricing and crucially, what's the problem it's trying to resolve?

First, what's the problem? Put simply, it's congestion on our roads. In the last nine years alone over six million more cars have appeared on our roads. That's partly because as a country we're better off and partly because people are travelling more for work, to do the shopping or for pleasure.

Today congestion is just about bearable. Edinburgh streets don't snarl up very often, but when they do it's exasperating. But we don't have to imagine what our roads might look like in 20-30 years time. Go to any major US or Asian city and you'll find gridlock 24 hours a day, seven days a week. Travelling by car is a nightmare and it's not just the frustration and costs, but also the huge pollution problems that are caused. Cities like Los Angeles or Beijing have a constant cloud hanging over them.

If things carry on like they are, our streets and motorways will become more and more congested, if we don't do anything about it.

So what's the answer? The truth is that there are many different things that need to be done. First, putting more money into public transport, buses and trains. We've done that.

The amount of money spent on trains has doubled in the last ten years with the result that Britain's trains are carrying more passengers than at any time in the last 60 years. Bus use too is increasing.

But most journeys we undertake are less than five miles from our front door. Trains don't help there. And people do take their cars to the supermarket, to the cinema and so on.

So public transport is essential, but we need to look at road use too. Here, we do need improvements to many roads, for example by-passes, managing the roads better, clearing up after accidents to keep traffic moving. But we can't build our way out of the problems we face. It would be hugely expensive in both financial and environmental terms. And in Edinburgh we fought off plans to build urban motorways into the city centre.

So new technology can help - and this is where road pricing comes in. Motorists are using sat nav equipment more and more - I guess it will be a standard fitting like a CD player in a few years time.

And there is something else. Some of the big car insurers are now looking at pay-as-you-drive insurance. You pay less if you drive during the day, and far more if you drive late at night, when it's more likely you'll be involved in an accident. Drivers stand to make big savings on their insurance bills and I suspect that it'll prove to be popular if the technicalities can be overcome.

It doesn't take a leap in the imagination to see that this approach could be used to encourage people to think about when they travel as well.

Road pricing means moving away from the present system of paying for road use and paying on the basis of distance travelled varied according to how busy a road is.

It is not the same as the congestion charge, which was firmly rejected by the people of Edinburgh two years ago. That was a charge deliberately designed to stop people travelling into the city.

Road pricing is a different way of paying for road use.

Can it work? There isn't any large-scale example of road pricing, though there are small scale examples in many parts of the world. That's why such a scheme would need to be trialled and that's why the Department for Transport is discussing options with a number of councils.

Of course it's easy to just say no and, of course, there are problems still to be resolved. But the growing problem of congestion is not going to go away.

So we do need better public transport - more buses, reliable services providing a real alternative. But it's also necessary to recognise the car is a fact of life. No one is saying don't use your car, but a system that meant that the cost of driving was more when the roads were congested might make people think about how they choose to travel and if we could persuade even a small number of people to change the time of day when they drove, congestion could be cut almost by half.

And this fits into the wider question of enabling people to work more flexibly - some people do work from home on certain days of the week or travel to work earlier or later in the day. As a government we've introduced the right to request flexible working for parents of younger children and carers. And not only is that good for families, but it also can cut down on rush-hour traffic.

And it's also good for employers and business. Lorries held up in traffic jams mean that shops don't get their deliveries when they need them. And many businesses need to make sure their employees can travel as efficiently as possible.

It's tempting to hope the problem will just go away, but it won't. Introducing a new system of paying for road use is probably ten years away, but we should be prepared to enter into debate now and think imaginatively about how we might use modern technology to resolve what is a growing problem. And it is important to win the public argument on the basis of the facts.

None of these problems is easily resolved, but future generations will never forgive us if we don't sit down and put in place something that's fair to motorists, makes its contribution to protecting the environment and, above all, avoids grid-lock. Sitting in a traffic jam going nowhere is no answer at all.

• Alistair Darling is MP for Edinburgh South West and former Transport Secretary