Rest and Be Thankful faces four days of diversions

Traffic will be diverted onto the Old Military Road

Four days of diversions are planned for the A83 Rest and Be Thankful in Argyll because of hillside investigations.

Transport Scotland said the work would inform the construction of a mile-long tunnel to protect vehicles from landslips.

The Rest and Be Thankful has regularly been closed by falling rocks and debris.

Drivers will be diverted onto the Old Military Road between 08:00 and 18:00 on 28 and 29 July, and on 11 and 12 August.

An artist's impression of the tunnel to protect vehicles from falling rocks

Transport Scotland said the work would involve specialist equipment, with diversions in place for safety reasons.

The A83 is an almost 100-mile (161km) major trunk road connecting the Mull of Kintyre and southern Argyll to the shores of Loch Lomond.

More than a million vehicles travel the route every year and it acts as an important transport link for mainland Argyll as well as the Inner Hebrides.

However, the Rest and Be Thankful section - a steep climb out of Glen Croe near Arrochar - is vulnerable to landslides and was closed for a total of 200 days in 2020.

When the road is closed, an old military road beneath is opened to traffic.

In 2023, the national transport agency unveiled plans for an open-sided shelter costing up to £470m as its preferred solution to landslip disruption.

Gordon Ramsay, Transport Scotland's project manager, said: "The works are essential ground investigations. These are necessary to inform the ongoing design development.

"The works will focus on the strength and depth of rockhead and the conditions below the surface of the ground."

Mr Ramsay said a crane would take up the width of the main road: "It will lift specialist drilling equipment up onto the hillside.

"It's essential for the workforce, and road users, that traffic is diverted during that period."