This practice is only allowed on the hard shoulder – many drivers receive hefty fines for doing so.

Law enforcement officers fine some 5,000 motorists each year on emergency lanes (BDU). This number is a poor reflection of reality, as we are seeing more and more illegal behavior on this lane located on the far right of the roadway on motorways. The emergency lane, approximately 3 meters wide, is a safety device that appeared on motorways in France in the 1960s. It is designed to allow drivers in difficulty to park without obstructing the flow of other vehicles.
But you can't do whatever you want there, even if it's sometimes tempting to use it. Especially during traffic jams when this lane seems to want to tell us "What are you waiting for to run over me, I'm free, you'll save time." But article R421-7 of the Highway Code stipulates that stopping without reason or driving on the emergency lane are strictly prohibited practices. So quickly forget the idea of taking a break in this safety lane, whether it's to eat, make a phone call or exchange drivers.

Before attempting to place their vehicle on an emergency lane, every driver must absolutely know what gives them the right to stop there. And there is only one valid reason: when they have no other choice but to stop immediately. This is the case for a serious breakdown that no longer allows the vehicle to move forward – following an accident or a mechanical problem – or if a passenger becomes unwell. Passengers are then asked to turn on their hazard lights, place their warning triangle at least 30 meters behind their car (if possible), and then move to safety behind the crash barrier while waiting for help.
Police vehicles, firefighters, ambulances, and tow trucks are the only ones authorized to drive on the hard shoulder to assist motorists in danger. All others are liable to a fine of €135. This penalty carries with it the loss of 3 points on their driving license for those caught driving on it to jump the queue. That's a lot for a few overtaking offences...
L'Internaute