At last Alistair Darling has found himself on the road to Damascus. The problem is he cannot decide how much he should be paying to use it. The conversion of the transport secretary from congestion-charging sceptic to enthusiast is largely thanks to the success of Ken Livingstone, the mayor of London, in making drivers pay to enter the heart of the capital. Mr Darling now accepts that there is no space, no money and no appetite for much more road-building. He also knows traffic fills new highways almost as quickly as they are built. The choice is stark: either introduce road charging or else accept that traffic jams will get longer.
Knowing what he would like to aim for - nationwide road-pricing - the transport secretary wants to have a debate on how best to get there. This is a mistake. Past occupants of Mr Darling's post have been listening to, rather than leading, debates on congestion charges since a British government report first advocated them in 1964.
To be fair, Mr Darling is clear about what he wants. Cars, in the future, will be fitted with a satellite tracking device to meter journeys at rates which reflect how busy the roads are. Drivers will be billed for their travel. But Mr Darling will have his work cut out in getting from the present to the future. He needs to start getting people used to paying for the scarce resource of road space. But in big urban centres, the transport secretary cannot impose new schemes - only local authorities can. That so few have come forward with innovative traffic-busting schemes is partly because of Mr Darling's reluctance to back Mr Livingstone's plan until it succeeded.
Putting tolls on big trunk roads, where the writ of the secretary of state does run, would, in many cases, simply displace traffic on to local roads. There are also important civil liberty issues at stake. Who will have access to the data stored and how long it is kept are questions that 24 million drivers will want answered before they accept a spy in the cab. Mr Darling should remind people that most of the population can already be tracked through their mobile phones.
To make the new charges acceptable to voters, Mr Darling is considering scrapping vehicle excise duty. Others decry the iniquity of high petrol taxes - which penalise rural drivers with no option but to take to (fairly) empty roads. In both cases the impression is given that congestion charging would be revenue neutral. But, as Professor Phil Goodwin points out, there is an unresolved tension between winning the political argument over road pricing by ensuring it is not seen as an another motoring tax and the benefit of using any extra cash to fund more public transport. Road pricing should also reflect the environmental damage caused by traffic. These points are key to changing the way we move around the country.
If motorists were presented with the true cost of their car journeys, they might decide to use buses or rail. Road use, a free good, should be priced and drivers charged. Mr Darling needs to abandon his cautious approach to charging motorists. The quickening pace of technology means a national scheme could arrive much sooner than the 25 years Mr Darling talks about. Congestion is not due to roadworks or accidents: it occurs when too many vehicles try to squeeze into too small a space. Public transport could help to cut congestion but at present it is more convenient to travel by car. Traffic jams are a case where individuals pursuing their own interests do not add up to the greatest good for the greatest number. The best way of achieving that is by road pricing.
