Transport Scotland has said that ground investigation for the upgrade of the A82 between Tarbet and Inverarnan is set to start on 26 March.
The ground investigation next to the shores of Loch Lomond, which is set to be undertaken by Soil Engineering Geoservices, is set to last for around 18 weeks.
The work has been valued at £3.4M.
The route is located within the Loch Lomond and The Trossachs National Park and is a complex site, which is physically constrained, with the loch on one side, and the hillside and railway on the other.
A Transport Scotland spokesperson said: “This ground investigation contract will help inform the design work for the vital upgrade to the stretch of the A82 between Tarbet and Inverarnan.
“We apologise for any inconvenience these works will cause and would thank road users and local people in advance for their patience during the works. The contractor will closely monitor the operation of the traffic management measures to ensure that any delays are kept to a minimum.