This is a frequently asked question, at least to me. Scientifically speaking, the consumption of one beer will not (of course) raise your blood alcohol level to the usually accepted legal level of 0.08%. However, if the cops find you with an open container of any alcohol in your car, you can be arrested. (At least, in Texas. they can.). Furthermore, MADD (mothers against drunk driving), and some other organizations, including some respected scientific organizations say that
any concentration of alcohol in your blood will impair your reflexes, and cause you to be a little slower in the case of emergencies. To be 100% safe, you shouldn't drink anything before driving.