A long, long, time ago, in 1491, when Anne de Bretagne (described in Wikipedia as "un personnage soucieux de défendre le duché face à l'appétit de ses voisins") married Charles VIII, uniting Brittany with the rest of France, one of the conditions of her marriage was that France was not allowed to levy road tolls in her homeland. Elsewhere in France, many of the motorways have been privatised and companies such as Vinci and Cofiroutes charge hefty fees for their use. While the tolls are expensive, they do pay for a high level of improvement and maintenance, meaning that many of them have 6 lanes and speed limits of 130km/h. In Brittany, on the other hand, the motorways are free to use, with no more than 4 lanes and 110km/h speed limits.
While I generally appreciate the fact that the private motorways allow me to get far away from Paris in a relatively short period of time, driving at 70 miles per hour instead of 85 (add ten for the average French driver!) and only having to worry about checking one wing mirror at a time is definitely a de-stress factor in Bretagne for me!