Transport for Scotland said that construction of a debris flow shelter – a tunnel with one open side – is the preferred option to address the challenges for the stretch of road known as Rest and Be Thankful between Argyll and Bute.
An online consultation process has now opened following design and assessment work on five options through the Glen Croe valley.
The debris flow shelters, to protect the road and its users from falling rock and debris, has been reportedly costed at £470m.
An online exhibition gives the public the opportunity to view and comment on the preferred route option.
Scotland’s minister for transport, Kevin Stewart, 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.
“Work will now be taken forward at pace to further develop our proposals, including the detailed development and assessment of the preferred option along with the preparation of an environmental impact assessment, draft road orders and draft compulsory purchase orders.
“At the same time as progressing the long-term solution, we are looking to increase the resilience of the temporary diversion route along the existing Old Military Road, having identified the preferred route solution for it late last year.
“The first phase of implementing the medium-term solution will begin later this year with realignment of the southern end of the route. This will increase resilience of the temporary diversion route by reducing the likelihood of closures due to flooding, meaning more certainty for locals and road users if the A83 has to shut due to adverse weather conditions.”