In the event of a breakdown or an accident it is a French driving rule (and common sense) that a warning triangle be placed behind the incident to warn approaching drivers.
Use your common sense when judging how far back down the road the triangle needs to be. Generally the faster the traffic flow the further the gap between the triangle and the incident should be to allow more reaction and braking time.
We suggest a minimum distance of 50 metres.
See out accident and breakdown page here and learn more about European breakdown cover here.