This is yet another moronic measure, right up there with the one banning speed camera locations on GPS. It's all about politicians being seen to do SOMETHING even if it's pointless and achieves absolutely nothing.
Honestly, if you're going to drive, have no more than the one (reasonable - not a long island iced tea for example) drink, et voilà. I see this sort of thing as fraught with difficulty ("but officer, I checked before I set off" and so on). It's probably also a ruse so that they have something to fine you for, particularly if you're a motorist visiting France - breathalyser kit past it's used by date for example.
Angry of St Germain en Laye
P.S. I'm entitled to pay hundreds of thousands of euros into the French public purse every year, yet I have no choice this weekend in which corrupt & preening self satisfied idiot will be fleecing me for the next five years. Vive la démocracie.
