A Preliminary Assessment of the Impact of Lowering the Illegal per se Limit to 0.08 in Five States

Johnson, Delmas Maxwell; Walz, Marie C. · 1994 · ROSA P / United States. National Highway Traffic Safety Administration

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Summary

This 1994 National Highway Traffic Safety Administration (NHTSA) technical report provides a preliminary assessment of the impact of lowering the illegal *per se* blood alcohol concentration (BAC) limit from 0.10 to 0.08 grams per deciliter in five U.S. states: California, Maine, Oregon, Utah, and Vermont. The study was motivated by NHTSA’s recommendation that states adopt the 0.08 limit, based on evidence that critical driving tasks are impaired and crash risk increases substantially at this level. Additionally, the Intermodal Surface Transportation Efficiency Act (ISTEA) of 1991 provided federal incentives for states to lower their BAC limits, prompting this evaluation to inform other states considering similar legislation. The researchers utilized data from NHTSA’s Fatal Accident Reporting System (FARS), which contains a census of fatal traffic crashes. The analysis focused on drivers aged 21 and older, comparing time periods before and after the implementation of the 0.08 BAC laws in each state. To ensure comparable crash patterns, the study matched seasonal periods (e.g., summer months before vs. summer months after) and used the latest available data from 1992. Six distinct measures of driver involvement in alcohol-related fatal crashes were examined: any alcohol (BAC > 0.01), intoxicated (BAC > 0.10), police-reported driver alcohol involvement, single-vehicle nighttime driver involvement, single-vehicle nighttime male driver involvement, and estimated alcohol involvement. Statistical significance was determined using a chi-square test for the difference in proportions at the α = 0.10 level. The results indicated that nine of the thirty comparisons across the five states showed statistically significant decreases in driver alcohol involvement following the legislation. Oregon exhibited the most consistent results, with significant reductions in four of the six measures, including a 13% decrease in police-reported alcohol involvement. Vermont also showed significant declines across three measures, with estimated alcohol involvement dropping by 40%. California and Utah each showed one significant reduction, while Maine showed no statistically significant decreases for any measure. In contrast, comparisons for the rest of the nation (excluding the five study states) yielded no statistically significant reductions. Although 21 of the 30 measures were not statistically significant, the majority of those still showed non-significant decreases. The report concludes that the implementation of 0.08 BAC laws, along with associated public information campaigns, is associated with reductions in fatal crash driver alcohol involvement. However, the authors note that these findings are preliminary and potentially confounded by other concurrent legislation, such as administrative license revocation laws. Consequently, NHTSA stated that additional, more in-depth analytical work was underway to isolate the specific effects of the 0.08 BAC limit from other factors.

Key finding

Significant decreases in driver involvement in alcohol-related fatal crashes were observed in nine of thirty measures across four of the five states studied following the implementation of 0.08 BAC legislation.

Methodology

dataset

Provenance

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Topics

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• alcohol
• drowsy as impairment
• dui enforcement

Information type

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• Empirical Findings: crash risk outcomes