Consider BAC. Technically, you're just not allowed to drive impaired. And different people function better or worse at the same BAC. But we have adopted a de-fa

Consider BAC. Technically, you're just not allowed to drive impaired. And different people function better or worse at the same BAC. But we have adopted a de-facto standard of 0.08%. The police don't prove in fact you were too impaired to drive, and posed a hazard to someone else. They just lock you up.