Ground works are set to begin on the £3 billion upgrading of the A9 to dual carriageway all the way from Perth to Inverness.
The work on the 5.59-mile Luncarty to Pass of Birnam section north of Perth will represent the first spade in the ground for the Scottish Government's target of completing the whole project by 2025.
A £1.3 million ground investigation contract is expected to be awarded early next month to Environmental Scientifics Group Ltd, and work should begin next month and last for four months.
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Transport Minister Keith Brown said: "These important ground investigations will give us the detailed information needed to progress the draft orders for Luncarty to Pass of Birnam section next year.
"They underpin the careful in-depth planning and design required for one of the biggest infrastructure projects in Scotland's history.
"Progress is also being made elsewhere on the A9 on the Kincraig to Dalraddy section (Inverness-shire). Tenders for ground investigation work will be sought early next month and these works are expected to start later this year, paving the way for construction to start in 2015/16."
Mr Brown added: "It is further good news that we are starting the tender process for the ground investigation work on the Kincraig to Dalraddy section.
"When completed, the A9 dualling programme will bring benefits to road users, communities and businesses who live along, or use, this important route which links central Scotland and the Highlands and Islands."