Construction has begun on the first section of the £3 billion A9 dualling programme.
Nearly 750,000 tonnes of excavation work will be carried out on the five-mile stretch from Kincraig to Dalraddy in the Highlands.
Estimated for completion in 2017, it is the first stage of the ambitious project to upgrade 80 miles of the key route between Perth and Inverness by 2025.
The A9 is often dubbed Scotland's most dangerous road due to the number of fatal accidents and average speed cameras have been installed in a bid to improve safety.
Keith Brown, Cabinet Secretary for Infrastructure, Investment and Cities, said: "It is no understatement to say that we are marking an important milestone in what will be one of the largest and most challenging infrastructure projects in Scotland's history.
"I am very proud that the Scottish Government is delivering this major upgrade and, in the weeks and months ahead, people will now see work on the ground as the road progresses.
"When this ambitious programme is complete, enormous economic and social benefits will be felt by communities along the length of the road, and beyond.
"Shorter term safety improvements for the A9 are already delivering positive benefits for the safety of the route, with preparation work on further dualling work also now starting to bear real fruit.
"With nearly three quarters of a million tonnes of excavation work to be carried out on this section here at Kincraig alone, we are at the start of a long journey to deliver the entire programme."
The £35 million Kincraig-Dalraddy contract will be carried out by a joint venture of Wills Bros Civil Engineering and John Paul Construction.
It will see the laying of more than 18 hectares of new road carriageway - the equivalent of 25 full size football pitches.
From September 21, a 40mph speed restriction will operate on the stretch as work is carried out.
A contractor spokesman said: "We are delighted to see construction get under way on the A9 Kincraig to Dalraddy project.
"Whilst some disruption to road users is unavoidable we would like to thank in advance the driving public and local communities for their patience and co-operation while we deliver this first leg of the A9 dualling programme."
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