Here is a profile of the N-154 to Spain.
Stop signs don't seem like something any reasonable person would consider to be an impediment to travel. There are plenty in the town - it took me less than 5 seconds to plop peg man and pan the street view image to a point where two were within view! Were they also prepared to argue that travel was not possible within their own town because of stop signs?
I don't think this stretch is actually numbered as N-154 in France. It is signed as French D68, the signs and road markings are all French. You can see the change at the (unsigned) border at LlÃvia.