The cut-price solution to traffic gridlock? Stop building roads and put in more speed cameras

Figures obtained by the Daily Mail reveal that costly road projects are spiralling out of control and costing up to £100million a mile - or £1,500 an inch.

As a result, ministers are set to axe a swathe of controversial road schemes, with those on the M1 and M6 most at risk.

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They face being replaced instead with far cheaper "active traffic management" schemes linked to speed cameras.

These include using motorway hard shoulders as extra lanes, introducing variable speed limits which reduce as traffic gets heavier and siting speed cameras to police and enforce the system.

It means thousands more drivers are likely to be hit with speeding fines. But ministers believe it is a far cheaper option for reducing jams than building new roads.

Fewer than half the Government's major road-building projects are being completed on budget, say critics.

Transport Secretary Ruth Kelly is set to back the switch from tarmac to technology when she publishes two major reports within weeks.

One, from the Highways Agency, was ordered by ministers into the spiralling cost of road projects.

The second highlights how technology such as cameras, road sensors and hard shoulders could prove a cheaper alternative to expensive road building.

The Government is expected to seize on both reports to back the widespread introduction of "active traffic management".

A trial of the variable speed limit system on the M42 showed that more than 95 per cent of drivers comply - fearing the risk of getting a ticket if caught on camera.

The M42 trial, and a similar scheme on a section of the M25, found that reducing the limit resulted in faster average journeys because vehicles were less likely to brake sharply, which causes tailbacks.

Fuel consumption fell by 4 per cent and harmful vehicle emissions by 10 per cent.

The Campaign for Better Transport has calculated from official figures that the most expensive conventional road scheme is the £100million per mile for the M74 near Glasgow, though the Highways Agency says the average cost for constructing a mile of motorway is £29.9million.

Rebecca Lush Blum, of the CBT, said: "Roadbuilding is bad news for the taxpayer as well as the environment.

"By contrast, active traffic management involves opening up the hard shoulder at peak times, with all lanes travelling at 50mph.

"This benefits motorists by smoothing out traffic flows, creating more reliable journeys, and reducing carbon emissions, pollution and accidents."

Figures from the Tories show fewer than half the Government's Highways Agency projects are meeting their budget. In 2006 only three out of ten completed road schemes came in on budget.

The RAC Foundation says 1,000 miles of major highways across Britain face gridlock by 2040 unless more roads are built.