Cutting roads and such into the sides of hills always carries a risk. Sometimes you can have enough knowledge and design for it. Sometimes not. And sometimes people don’t even know or worry about the hazards until too late.
But at some point even the Grand Teton will end up on the valley floor.
Shift happens!
Not too far from my home the county highway department removed a half?-century old rock wall(and some of the hillside behind) that adjoined the road,claiming the wall “deflected the snow from the plows back onto the road”. Within two weeks the hillside slumped ,bringing utility poles to near 45 degrees ,and the road had to be closed briefly.
Today’s “engineers” act as though all the old knowledge is to be disregarded.
In other cases,that road across the face of a hillside stayed put for the horses and wagons but not once 20 ton trucks began pounding it!
The mountain side is seeking it’s natural angle of repose