Original Articles
Evaluation of the effectiveness of low blood alcohol concentration laws for younger drivers

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Abstract

Objective: This study aimed to determine whether low blood alcohol concentration (BAC) laws among younger drivers reduce motor vehicle injuries.

Search Strategies: 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.

Selection Criteria: 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.

Data Collection and Analysis: 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.

Main Results: 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. The 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%.

Conclusions: 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.

Introduction

Compared to all age groups, young drivers have the highest risk of fatal crashes. Of the 56,793 American drivers involved in fatal crashes in 1996, 8,054 were 20 years of age or younger. These young drivers were involved in fatal crashes at a rate of about four times the rate for drivers 25 to 65 years old.1 Of these young drivers, 21% were killed in crashes in which the driver had a BAC of greater than 0.10%.

Over the years, we have had considerable success in lowering the percentage of teenagers killed in alcohol related crashes. In 1980, 53% of the teenage drivers killed in crashes had a blood alcohol concentration (BAC) of greater than 0.10%. By 1987, only 28% of the fatally injured teenage drives had BACs over 0.10.2 In 1996, only 21% had BACs over 0.10. In large part, this reduction in alcohol-related motor vehicle crashes among teenagers can be credited to the increase in the minimum drinking age to 21 years in all states.3

However, even with these laws, teenagers continue to drink and to die in motor vehicle crashes. To address this residual problem, 49 states have passed “zero tolerance” laws establishing lower legal blood alcohol limits for younger drivers than for adult drivers.

We conducted a systematic review to determine if “zero tolerance” laws have reduced the number of alcohol-related injuries and fatalities among young drivers.

Section snippets

Methods

Search strategy for identification of studies: Details of the search strategy are reported in the introductory article.4 The Cochrane collaboration methodology was used to search a variety of databases. Studies were not restricted to English and could come from both published and unpublished sources. We searched the following databases: MEDLINE 1966–1997, EMBASE 1974–1997, National Technical Information Service (NTIS), 1983–1997, Educational Research and Improvement Clearinghouse (ERIC),

Results

All six studies (see Table 1) showed a reduction in the outcome variable after the implementation of the law, although, for three of them, these reductions were not statistically significant. The methods for analyzing the data varied among the six studies. Thus, they can not be compared precisely. The study with the lowest reduction in the outcome variable10 was also the study with the least power. This study only had a power of 70% to detect a hypothetical 10% decline in serious casualty

Discussion

Since it is unlikely that these restricted blood alcohol concentration laws will ever be tested using a randomized controlled study, we must pay special attention to the methodologic weaknesses of ecologic studies. In pre- and post-studies and interrupted time series, the most troublesome threat to validity is historical bias.12 Historical bias refers to the possibility that something else may have occurred at the same time as the intervention and that this unknown factor, rather than the

Conclusions

The evidence appears sufficiently strong to justify the introduction of these restricted BAC laws in other jurisdictions. However, additional evaluations of these laws would seem prudent to address the possibility of historical bias. At least two such evaluations are currently underway: one in California and the other in Iowa. In 1997, the U.S. Congress voted to withhold a portion of Federal highway construction funds from states that did not adopt zero-tolerance laws. Consequently, by May

Acknowledgements

We would like to thank Kristi Ferguson, PhD, for reviewing this paper.

References (12)

There are more references available in the full text version of this article.

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