When we visited Ireland many years ago, Pepper Mill and I got stuck on a road going into some town in southeast Ireland. We turned around and simply avoided the town. It turned out that a bus had blocked traffic (I don’t think it got stuck, as in the OP. It’s just that traffic coming after it blocked its way when the going got too narrow, and nobody could back up because everyone would have to back up.)
So evidently what happens is that traffic slows to zero and everyone’s stuck until cars peel out one by one. If there are few or no alternate roads, this can take forever.