Effects of Low Doses of Alcohol on Driving-Related Skills: A Review of the Evidence

Moskowitz, Herbert, 1925-; Robinson, C. D. · 1988 · ROSA P / United States. National Highway Traffic Safety Administration

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Summary

This 1988 literature review, conducted for the National Highway Traffic Safety Administration, investigates the effects of low doses of alcohol on driving-related skills to determine the blood alcohol concentration (BAC) at which impairment first appears. The study was motivated by the need for scientific evidence to inform public policy decisions regarding legal BAC limits, particularly as epidemiological data indicated increased accident risks at levels well below the then-prevailing 0.10% limit. The authors sought to establish whether a lower threshold exists below which alcohol does not impair driving performance. The researchers conducted a comprehensive review of experimental literature, initially identifying 557 citations. After excluding studies for reasons such as irrelevance to driving, lack of methodological detail, or inability to compute BACs, 177 studies were included in the final analysis. A key methodological feature was the independent computation of BACs for each study based on reported dosages, subject gender, and body weight, using a conservative metabolism rate of 15 mg/100 ml per hour. This approach ensured that estimated BACs were likely higher than actual levels, providing a conservative estimate of impairment thresholds. The studies were categorized into nine behavioral areas: reaction time, tracking, concentrated attention, divided attention, information processing, visual functions, perception, psychomotor skills, and driver performance. The review found that 158 of the 177 studies reported impairment in one or more skills, with only 19 finding no impairment. Impairment was significant at BACs of 0.05% and first appeared in many areas at BACs of 0.02% to 0.03%. Divided attention performance was the most sensitive area, with impairment beginning below 0.02% and a majority of studies showing effects at or below 0.05%. Tracking performance also showed early impairment, with most studies reporting effects at or below 0.05%. In contrast, concentrated attention was the least sensitive, with no impairment found below 0.05%. Complex reaction time was impaired at lower BACs than simple reaction time, but typically at higher levels than divided attention. Visual functions like oculomotor control showed impairment at low BACs, while others like visual acuity did not. Psychomotor skills requiring coordination were impaired at lower BACs than other psychomotor tasks. The authors concluded that there is no lower limit to alcohol impairment of driving-related skills; impairment begins at very low BACs, particularly affecting divided attention and tracking. The findings suggest that scientific evidence does not support a BAC threshold below which drivers are unimpaired. The review highlights that recent studies, which examined lower BACs and more complex behavioral tasks, detected impairment at significantly lower levels than older literature. These results imply that legal BAC limits should consider the early onset of impairment in critical driving skills, particularly those involving attention and information processing, rather than relying on higher thresholds that may not reflect actual performance deficits.

Key finding

Impairment in driving-related skills was found at BACs of 0.05% and first appeared in many areas at BACs between 0.02% and 0.03%.

Methodology

review

Provenance

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Topics

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• alcohol
• drowsy as impairment
• polydrug
• cannabis