Recently, occurrence of alcohol-involved traffic accidents is increasing while all the accidents by violation of law except drunk driving. Traffic accidents by drunk driving has a great external cost. In detecting drunk driving, blood alcohol content Many studies reported close correlation between blood alcohol content and traffic accidents by drunk driving. The risk of traffic accidnet increases exponentially as blood alcohol content increases. To control traffic accidents by drunk driving, decide target population. Heavy drinkers are few and responsible for a small part of the loss while casual drinkers are many and responsible for a large part of the loss. Casual drinkers need to be included in the targer population for the control of traffic accident by drunk driving. Stragegies to reduce the quantity of alcohol consumed, change the pattern of drink, such as frequency of drinking, raise of perceived risk of accident need to be sought.