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Lower blood alcohol laws for younger drivers are effective, according to UI study

IOWA CITY, Iowa -- "Zero tolerance" laws establishing lower legal blood alcohol limits for younger drivers appear to be effective in reducing motor vehicle injuries and fatalities, according to researchers at the University of Iowa.

Craig Zwerling, M.D., Ph.D., professor, and Michael P. Jones, Ph.D., associate professor, both in the UI department of preventive medicine and environmental health, evaluated the findings of six studies from the United States and Australia that looked at the impact of laws limiting the blood alcohol concentration (BAC) permitted in drivers under age 21. All of the studies showed a reduction in the outcomes measured even though, in some cases, the reductions in injuries or fatalities were not statistically significant.

"Our evaluation of what's happened in the United States and Australia shows that the results as a whole are not overwhelming, but they do suggest that these kinds of laws have a modest effect--roughly a 15-20 percent decrease in crash rates among young drivers," Zwerling said.

He added that the laws with lower BAC levels seemed to be slightly more effective than the laws that had higher BAC levels. For example, in states with 0.02 percent BAC laws, the reduction in injuries or fatalities averaged 17 percent, whereas in states with 0.04 to 0.06 percent BAC laws, the reduction was only 7 percent.

In Iowa, a BAC limit of 0.02 percent for drivers under 21 was instituted in July 1995.

The UI researchers searched electronic databases, reference lists of past studies and governmental agency publications, and contacted experts in the field to select the studies they evaluated. Studies were included if they provided objectively measured data on an injury outcome--nighttime injuries, for example--and if they used an appropriate comparison group to assess the impact of the law. Three of the studies involved younger drivers in Australia.

Zwerling, director of the UI Injury Prevention Research Center, noted that raising the legal drinking age from 18 to 21 in the United States several years ago has had the biggest influence on lowering injuries and fatalities among younger drivers. Though not making as significant an impact, "'zero tolerance' laws do seem to be working. That's the bottom line," Zwerling said.

The UI study was published in the January 1999 issue of the American Journal of Preventive Medicine.