The twisty bit was called the Devil's Elbow [1], I remember going over it as a child before the modern road bypassed it. My parent's first car was a Hillman Imp too, I used to sleep on the shelf over the rear engine for part of trips up to Aberdeen.
I have had to fit chains to my car to get over the Cairnwell Pass, nothing passed me while I was fitting them and I could see people turning around lower down the hill, didn't see any gritters.
[1] https://en.wikipedia.org/wiki/Cairnwell_Pass