This study describes a field experiment designed to test the impact on drinking of providing “Know Your Limit” (KYL) BAC estimation cards to individuals in a natural drinking environment. Participants were randomly sampled as they entered Mexico for a night of drinking. Researchers interviewed them, and randomly assigned them to one of six experimental conditions. Participants were re-interviewed and breath-tested when they returned to the United States. The experimental conditions included providing generic warnings about drinking and driving, giving out gender-specific BAC calculator cards (KYL cards), and providing incentives to moderate their drinking.
Cueing participants about the risks of drunk driving resulted in significantly lower BACs (relative to control) for participants who indicated that they would drive home. Providing KYL matrixes did not reduce BACs, and, in fact, some evidence suggests that KYL cards undermined the effect of the warning.
KYL information does not appear to be an effective tool for reducing drinking and driving. Implications for prevention and future research are discussed.