Britain's road-building programme will cost the taxpayer billions of pounds more than expected, with some major projects more than doubling in price in five years, research indicates.
Figures compiled by the Campaign for Better Transport (CBT) pressure group showed that 41 road projects which had been calculated to cost £4.45bn will now cost taxpayers £8.12bn – a rise of almost 83 per cent.
Critics blame the Highways Agency, maintaining that at the time the projects were approved it made major errors in its calculation of inflation and the likely costs of materials, labour and compensation for homeowners. The study revealed that improvements to one stretch of the A14 between Ellington and Fen Ditton in Cambridgeshire had risen from an estimated £490m in 2003 to £1.2bn.
Even the most conservative costing predicts that improvements to a stretch of the A46 between Newark and Widmerpool, in Nottinghamshire, will run to more than three times the original costing of £82m.
The Highways Agency is criticised for basing its inflation predictions on the retail price index, which tracks the prices of household items, at a time when high global demand for building materials means inflation in the construction industry is much higher.
The CBT said the agency had also been "wildly optimistic" in its predictions of the level of opposition to road schemes, which has delayed several projects.
A spokeswoman for the Highways Agency said: "Inflation in the construction industry has approximately doubled in recent years. This is the main reason for the change in cost estimates," and added: "We have made significant improvements to the way we estimate the costs of planned road schemes."
Green campaigners said the rising costs have undermined the argument that roads are a cost-effective way of meeting transport needs. Richard George, the CBT's roads and climate campaigner, said the argument given for building roads was that they are the "cheap option", but added: "It would be much harder to make a case for these road projects using the bill they have left us with now."
Norman Baker, the transport spokesman for the Liberal Democrats, said: "If the estimates had been anywhere near the latest revised figure it is questionable whether the schemes would have got the go-ahead." Headded: "It is very convenient for the Government that these wildly inaccurate cost estimates happened to be low enough to get the road schemes to pass the benefit-cost analysis."
He called for greater investment in the rail network "before even more taxpayers' money is thrown down the drain".