What are the speed limits, and are they checked?
Motorways (in French they are called Autoroutes) are normally 130 kph, except when it rains, then they go down to 110 kph. Secondary roads, country roads and national highways are limited at 90 kph. Some dual carriage roads (2 x 2 lanes) are limited to 110 kph.
Cities are limited to 50 kph, but more and more are lowering portions of the city to 30 kph.
As for the policing of the speed limits, rest assured: they are checked almost everywhere! France’s government has fallen for the speed radar, an autonomous, digital and highly sophisticated unit that often checks not only several lanes, but also checks traffic in the opposite lanes. Photos are made and immediately sent wirelessly to a computer where it is analysed. License plates are read and the fine and license points (in France you start with 12 points and every time you get caught being naughty, they subtract points until you forfeit your license) are mailed to your house days after the speeding. There are also several unmarked cars patrolling the roads equipped with these sophisticated radars.
They have also started placing radars before road works. These radars are mobile, so can be placed in many different areas where there is work in progress.
Officially, international license plates can be ticketed by these smart machines, but in practise this would require the police in your country to come and get the fine and send it to France: That’s not going to happen! But if you are driving a rental car, expect to have to pay when returning the car.
The only plus point is that most fixed radars are marked with sign signalling a radar within the next 5 kilometres.