About 70,000 tonnes of existing material will be re-used

Resurfacing work near Buckfastleigh will last for six months and reduce the road to one lane in both directions.

Experts have warned that at the busiest times traffic could be queuing for five miles at the start of the roadworks.

Cones have been laid on part of the carriageway between Peartree and Drybridge, ready for work to begin.

The work will cost about £8m. In the largest project of its kind, the old surface will be recycled at the scene before being re-laid.

About 70,000 tons of material will be taken from the road, then reconstituted and relayed, potentially saving thousands of lorry journeys.

The Highways Agency said junction closures and contra flows are also going to be necessary.

The roadworks are expected to last until Easter.