Excavation work has started on the £371m tunnel taking the A3 under the Devil's Punchbowl in Surrey.
The government says the tunnel will ease congestion
Transport Secretary Ruth Kelly watched as the first sections of earth were dug from what will be the longest road tunnel under land in the UK.
The twin-bore Hindhead tunnel, which completes the dual carriageway between Portsmouth and London, is scheduled to open to traffic in summer 2011.
Ms Kelly said the scheme would protect the landscape and ease congestion.
She added: "This scheme will bring real benefits to local people, whether they are drivers, horse riders, cyclists or pedestrians, as well as create a better habitat for local wildlife and preserve the beauty of the landscape.
"I congratulate the Highways Agency and its contractors for taking such special care during the site clearance to minimise the impact on the protected species of the local wildlife."
In October 2007 a viewing platform and visitor centre was opened to keep people up-to-date with progress.
The platform is just off Footpath 95 near the northern tunnel entrance.
The Devil's Punchbowl is a Site of Special Scientific Interest and also part of an international special protection area designated under the EU Directive on the Conservation of Wild Birds.
The government has said the twin-bore tunnel will remove 30,000 vehicles a day from the heathland site.