As a DUI lawyer, I get asked the question, how many drinks can I have and still drive a car. The best answer is none. If you get stopped by the police, the first thing the officer will ask you is "have you been drinking tonight sir/mam?" If you had even one or two drinks, your answer to that question will be "yes I have been drinking". So if you wanted to get the officers attention, that should do it. When I used to ride with the police and sherrif on DUI patrol during my State Attorney training, almost every person we stopped for DUI said "I only had two beers", this seems to be the standard answer that everyone thinks police want to hear. By admitting you had two beers you just made one element of the officers case against you, that you had consumed alcohol. All he has to prove now is that your normal faculties are impaired, and that can be his subjective opinion. So I suggest a designated driver if you want to be safe and dont want to lie when the police officer askes you if you had been drinking. You dont have to lie, you could refuse to answer the question, but that will get the officers attention possibly more than admittng two beers. If you insist on drinking and driving there are some charts that give you an estimate of your blood alcohol level by weight. A general rule of thumb is one drink per hour, with a glass of water between drinks. This does not mean you can drink for ten hours. What is meant is that two or three drinks over a two or three hour period with water inbetween, and you may be ok to drive.
be safe - charlie