Most radar zones are posted with a sign.
I would say the some radar zones are posted, many are not, and there are a few mobile units that are used by police to surprise the locals who generally have all of the camera positions memorized.
One thing I have unscientifically surmised is that WAZE efficiency in finding the fastest route is dependent on the number of people using the app in a given area.
It is my understanding that Waze uses mobile phone signals located on roadways to analyze traffic and does not limit its data to just those phones which may be using their app.
Autoroute speed limits, among other roadways, drop when it rains and I'll agree that no network will be able to make a determination when you speed should be lowered. Speed limits in France used to be relatively easy to follow: 50 kmh in towns, 90 kmh outside of city limits. However, now there is 30, 50, 70, 80, 110 and the autoroute speeds (130). It's sometimes difficult for the non resident to really know what the speed limit should be.
Speed limits are not the only rule one needs to know. There is the priorité a droite, and when on mulit-lane roads: no passing on the right and always maintaining yourself in the far right lane.