Minimum purchase age laws: How effective are they in reducing alcohol-impaired driving?

Young drivers are less likely than adults to drive after drinking alcohol, but their crash risk is substantially higher when they do. This is especially true at low and moderate blood alcohol concentrations (BACs) and is thought to result from teenagers' relative inexperience with drinking, driving, and combining the two. Since July 1988, all 50 U.S. states and Washington, D.C., have had laws that require people to be at least 21 years old to purchase alcohol. Many other countries, however, allow people younger than 21 to drink alcohol. Minimum legal drinking ages are 16 to 18 in most European countries, 18 to 19 in Canada, 18 in Australia, and 20 in New Zealand. Laws that establish a minimum age to drink alcohol are the primary legal mechanism limiting teenagers’ access to alcohol. In the United States, zero tolerance laws that make it illegal for people younger than 21 to drive with any measurable amount of alcohol in their bodies, and minimum legal drinking age (MLDA) laws of 21 are the primary legal countermeasures against underage drinking and driving. This paper summarizes trends in alcohol-impaired driving among people younger than 21, the history of minimum legal alcohol drinking age laws, and the evidence of their effects. Laws vary with regard to whether they prohibit the purchase, consumption, or possession of alcohol by underage people (here referring to those 20 and younger). For simplicity, the terms "drinking age" and "minimum legal drinking age," collectively abbreviated as MLDA, are used to refer to all of these types of laws. The paper focuses primarily on the United States, where the bulk of research has been conducted.