The A683 between Kirkby Stephen and Sedbergh will be closed for four weeks for repairs.
Work will begin on Monday, September 19 to repair a landslip which happened during the storms in November 2020.
Cumbria County Council said: “Due to the complex nature of the slip and the environmentally sensitive location on which it is situated, there has been a lengthy design process to deliver the repair work.”
The full road closure will cause significant disruption, the county said, due to lengthy diversions and lack of any local roads.
The closure point is located just to the north of The Cross Keys Inn, next to the River Rawthey.
The county added: “The full closure of the road between Sedbergh and Kirkby Stephen on A683, is unfortunately necessary for the works to be compliant with current health and safety legislation. There is not sufficient remaining carriageway width available to allow traffic past the excavation once the works begin.”
The county council has planned for a permanent footpath for cyclists and pedestrians. It said it was considering extending the width to allow quadbike access for livestock.
However, a temporary road cannot be constructed due to the slope above the road and the need to undertake drainage work.
There will be a diversion in place, via A685, M6 Junction 38 – Junction 37 and then A684 for HGVs and motorway permitted traffic.
A second diversion via Mallerstang will be signed for light vehicles and motorway prohibited traffic only. This route has an 18 tonne weight restriction and is not suitable for HGVs.
The county council is working with contractor Metcalfes to complete the works as efficiently and as safely as possible, it said. The contractor will be working Monday to Saturday with extended hours to reduce the time of the closure.
The county council has asked people to contact the Highways Hotline on 0300 303 2992, if they have any questions or queries.
Cllr Keith Little, Cumbria County Council cabinet member for highways and transport, said: “We apologise for the relatively short notice on the start date. The environmental consenting process for this type of work is lengthy and involves liaison and approvals from various organisations and interested parties which can be a challenging process.
“We understand that these works will be disruptive and apologise for this; however, they are necessary to prevent the potential loss of a larger section of the A683, this winter. To maintain the safety of the crews working and the safety of the travelling public, it is not possible to allow traffic past the excavation once the works begin due to the width of the road.
“The slope provides support to the carriageway and its condition is deteriorating rapidly. A large section of the northbound carriageway has now been undermined and has collapsed. If we do not intervene and take action to remedy the situation whilst we have the opportunity, there is a real risk that the slope will not survive another winter, which could lead to the long-term full closure of the route.
“The highways team and the contractor will look to remove the closure as soon as possible and will operate under temporary traffic lights, whenever possible, so that the road can be reopened as soon as we can safely do so.
“Our priority is public safety, and I am pleased that we are making these improvements and I would like to thank the residents and businesses for their support and would also like to apologise for the inconvenience these necessary improvements cause.”
