So called "zero-tolerance" laws which specify very low or zero legal BAC limits for drivers under age 21 have resulted in declines in driving after drinking and fatal and non-fatal traffic crashes of 4 to 24% (Shults et al., 2001; Wagenaar et al., 2001).
In their systematic review, the Centers for Disease Control and Preventions Task Force for Community Preventive Services identified 11 studies, meeting their inclusion criteria, examining the effects of such "zero-tolerance" laws on alcohol-related traffic crashes. They concluded that zero-tolerance laws reduced fatal and non-fatal traffic crashes by as much as 25%. Moreover, a study of teens in 30 states found a 19% reduction in driving after drinking as a result of laws specifying a zero or very low BAC for young drivers (Wagenaar et al., 2001), and a study of college students found an 11% reduction in driving after drinking (Liang and Huang, 2008). Finally, in addition to the substantial effects specific to driving-after-drinking, Carpenter et al (2007) found that the zero BAC laws reduced overall teen drinking by 4% and heavy drinking by 6%.