As long as a drinker keeps his or her blood-alcohol level below the legal limit, that person's driving abilities won't be noticeably impaired. Marijuana and other illegal drugs do not have noticeable effects on driving skills after the high has worn off. On weekends, between 10PM and 2AM one out of every 5 drivers is impaired. Coordination is the first physical ability to be impaired by alcohol. If someone is not visibly impaired, he or she is probably not too drunk to drive.
Alcohol is the most commonly used intoxicating drug.