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