Expected to cost around £470m to build the protectect tunnel is now the preferred option to protect vehicles from falling rocks on the Rest and Be Thankful section of the A83 in Argyll.
The selection of the preferred option follows design and assessment work on five options through the Glen Croe valley.
Debris flow shelters have been successfully used across Europe and beyond for many years.
Minister for Transport Kevin Stewart MSP said: “The Scottish Government has been working tirelessly to find a long-term solution to the landslip risks at the A83 Rest and Be Thankful.
“The identification of the preferred route option through the Glen Croe valley is a very important milestone in finding a solution to this long-standing problem.
“The proposed new debris flow shelter will help protect the road and road users from future landslides.