gribley, I was touring in Normandy with a friend a few months ago. We actively sought out little roads. The narrowest ones were the best ones because they were devoid of traffic. It really wasn't the slightest bit scary. I can imagine that if we had been driving a car, it might have felt different. One of the things that make France so great for touring is that outside of the mountains, there is a superb network of small secondary roads with very little traffic.
We spent a couple of days biking on the Channel Islands. The roads there were much narrower than in Normandy. It was often unpleasant on Guernsey because many of the narrow one-lane roads had lots of traffic. I think that was because other roads were being worked on, so traffic was diverted to the country lanes we happen to have selected.