The Highways Agency is building a new retaining wall and improving safety barriers and drainage on a stretch of the A66 between Appleby-in-Westmorland and Warcop.
The A66 links the A1 at Scotch Corner with the M6 at Penrith and the section near Appleby is used by almost 13,000 vehicles every day.
Engineers will build a new 280-metre-long retaining wall on the southern side on the road, near Sandford, to replace the existing wall and support a section of road which runs alongside farmland.
They will use gabion baskets – wire boxes filled with rock – to build the wall.
Improvements will also be made to the drainage on a 150-metre section of the embankment on the southern side of the A66 near Appleby.
The work is due to be completed by mid-November.
Peter Gee, the Highways Agency’s Service Delivery Manager, said: “This is an important piece of work which will help to make the section of the A66 near Penrith safe to use for years to come.
“The new retaining wall will ensure the stability of the road, and we’ll also be making improvements to the safety barriers and drainage.”