From what I can tell you get aires with facilities such as hookup, water, and waste watr disposal, these ones are off the motorway.
Then you have the ones on the motorway itself which can be anything from a layby to a picnic area with play park and food.
I'm thinking of stopping for a single night in one of the motorway ones, is that allowed or are the police likely to move us on?
I've hear stories about robbery etc, I'm not too worried about that, I'll take my chances. more concerned the about the police.....esp as I plan to sling a hammock off the back of the car for a decent kip.
Don't forget to leave a review of the French and other European campsites you have visited!
You can stay overnight on the motorway aires, and people have all sorts of sleeping arrangements - sometimes sleeping on mattresses on the grass verge! However, there are aires which are safer than others, so it very much depends on which way you are heading, and where the local 'crime wave' is at the moment. In other words, wherever you are you may, or may not be, safe. If you're a long traveller, as I suspect a hammock for two might be difficult, then it would make sense to pack a pop up tent and stay overnight on a campsite somewhere near your route.
We're probably going to be stopping somewhere around Tours, I remember last time I was there we stopped at an aire that was huge,set well back from the road with lots of open grass space, trees, picnic area and toilet block including vending machines.
It was pretty quiet mind you, so maybe not the safest place if anyone did try it on.
If you do stay on an aire then please make sure it's the fully serviced type, with fuel station, restaurant and toilet blocks. Those quiet picnic aires are not the safest places at night, and even though we've been 'doing' France for thirty-odd years I wouldn't stay on one.
Like Francais, these days I would stay in a hotel, but my sons (in their thirties) do sleep overnight on aires still - but there is usually a car full of them and they have never reported problems.