The number of US teenagers involved in fatal drunk-driving crashes has declined because of laws that raised the legal drinking age to 21, according to a new study.
Researchers found that two "core" drinking-age laws passed in all US states in the 1980s were responsible for an 11 per cent decrease in the number of drunk teenage drivers involved in fatal crashes.
The two laws made it illegal for anyone younger than 21 to buy or possess alcohol.
The findings, the researchers say, suggest that calls for once again lowering the minimum drinking age in some states could end up reversing those gains.
In 1984, the U.S. passed a federal law that spurred all states to raise their minimum drinking age to 21.
Studies since then have suggested that the move was having an effect on road deaths, but it was hard to disentangle the impact of the law from other factors - like safer cars and tougher laws against drunk driving.
For the new study, researchers at the Pacific Institute for Research and Evaluation in Calverton, Maryland, used federal data on state drinking laws, as well as information from a national surveillance system of fatal traffic accidents to help account for these other factors.