I guess that passing places are something that many drivers never come across.
This sign is on a road that leads from near my house to the nearest motorway junction. It’s not quite a single track road – two cars can pass side by side – but they’re almost always going very, very slowly and taking great care!
The Passing Place, then, is for those parts of the road that are too narrow for two cars to pass. There’s a temporary widening of the road, like a lay-by, where the two vehicles can pass one another.
I certainly don’t know of many single track roads south of the Highlands; the Passing Place sign is surely something of a rarity.
And if the trees aren’t cut back a little, this one will have totally disappeared into the foliage!