We just tell them the truth. My AH is preparing to move out. DD14 will be visiting him. I plan to take her/pick her up as much as possible and she will ride with her older brother sometimes, too. We discussed not riding in a car with anyone who we know to be drinking or suspect has been drinking (friend, parent, family member.) I told her I would rather her wake me up in the middle of the night than ride with anyone she suspects has been drinking, her dad included. I also told her that she can call me any time to pick her up from AH.