Craig Zwerling, Michael P. Jones

This study aimed to determine whether low blood alcohol concentration (BAC) laws among younger drivers reduce motor vehicle injuries. We used Cochrane Collaboration search strategies of electronic databases, reference lists of past studies and reviews, governmental agency publications, and direct contacts with experts in the field. Studies were included if they provided objectively measured data on an injury outcome and if they used an appropriate comparison group to assess the impact of the law. Six studies met selection criteria. We abstracted information using standard data collection sheets. Since the studies all were of ecologic designs, we did not carry out any pooled analyses. All six studies showed a reduction in injuries or crashes after the implementation of the law, although, for three studies, these reductions were not statistically significant. This study with the smallest reduction in injuries was also the study with the least power. This study only had a power of 70% to detect a hypothetical 10% decline in serious injuries. Reductions in outcome in the other studies ranged from 11% to 33% with a cluster of parameter estimates just under 20%. One study evaluated laws with differing levels of BAC and found a dose-response effect. The greatest reduction (22%) was reported for nighttime, single vehicle fatalities in those states with zero BAC laws. In states with 0.02% BAC laws, the reduction averaged 17% and in states with 0.04 to 0.06% BAC laws, the reduction was only 7%. Despite the methodologic difficulties of ecologic studies, the six studies reviewed represent accumulating evidence in support of the effectiveness of these laws. The sum of the evidence is strengthened because similar results were found in different countries (Australia and the United States), using different laws (some aimed at younger drivers and others aimed at inexperienced drivers), using different outcome variables (fatalities, injuries, and crashes), and using different research methodologies (interrupted time series and pre- and post-studies). In addition, the largest U.S. study found that laws with lower BAC limits resulted in greater casualty reductions, analogous to a dose response effect.