Hi, if you're using the old N roads, then various places have narrow areas (or did last time we were down that way) and increasing amounts of traffic calming to encourage traffic out of the villages and on to the autoroute. The best way to see these for yourself (rather than rely on my description) is start from Vienne on Google maps, and follow the N7 route down the Rhone Valley. Vienne is the end of the free section of autoroute which takes you through Lyon.
Le Peage de Rousillon is one town where there is a quite narrow section, with traffic calming and one way streets with bollards separating two lanes of traffic as is Saint-Rambert-de-Albon. If you want to see more details, then use Street View to see the details. You can follow the road down and see each village, and examine the details for yourself using Street View, then decide whether it's worth paying for that section and using the autoroute. I think it's probably easier to see these things for yourself, rather than listing everywhere you might find a hold-up.
My OH has nerves of steel, but I always refused to tow on that section and we sometimes used to break our budget and spend some money on tolls if we got fed up.
Having discovered an alternative, and easier route, to the Med at the western end, that's now our route of choice - down the free A75 which is autoroute, but doesn't cost a penny!