No one should step into a car that has over 1 drink per hour period.  That was the given on the Ophra show which everyone knows I love!  After that anyone has some sort of impairment.  When we are driving, we all deserve to know that all the people in the cars around us are aware of their surroundings.  Too much can happen without the addition of alcohol.  Blind spots, slippery roads, tires blown out.  Don't give the excuse you should never enter the road when you are blisted.  Ophra had an actress on her show that was convicted - she never drove when drinking - except her husband this one day told her that he needed her to drive - she thought she was okay - thought she hadnt drinken much - just 2 drinks at a pool party.  She rolled the car and broke the collar bone of one of her children.  She feels like maybe her glass was being refilled during the day without her knowledge and she didn't realize it.