Anyone standing on the hard shoulder on French motorways should be wearing a high visibility vest/jacket according to French driving regulations.
It is a minimum requirement that at least one Hi Viz should be kept in the vehicle in the event of breakdown etc for the driver. The vest should be inside the cabin of the vehicle not stored in the boot or in a roof top box etc as you should be able to reach it and put it on before getting out of the car.
But the law clearly states that every individual stood on the hard shoulder should be wearing a vest, so ideally you need one for every passenger in the car.
We put one Hi Viz Vests into our "All In One Travel Kit" and individually and you can buy them here as a single item or as an addition to the All In One Kit for extra passengers.
As a separate item to be posted on their own they are £4.95 each, however if you buy an all in one kit or a single one at £4.95 then you can add additional ones at just £2.95 each.