Effects of acute alcohol tolerance on perceptions of danger and willingness to drive after drinking

Abstract

Rationale: Drinking and driving is associated with elevated rates of motor vehicle accidents and fatalities. Previous research suggests that alcohol impairs judgments about the dangers of risky behaviors; however, how alcohol affects driving-related judgments is less clear. Impairments have also been shown to differ across limbs of the blood alcohol concentration (BAC) curve, which is known as acute tolerance.

Objectives: The objectives of this study were to examine whether perceptions about the dangerousness of driving after drinking and willingness to drive differed across the ascending and descending limbs of the BAC curve and to test whether reductions in perceived danger were associated with willingness to drive on the descending limb.

Methods: Fifty-six participants were randomly assigned to receive either a moderate dose of alcohol (peak BAC = 0.10 g%) or placebo. We assessed perceived dangerousness and willingness to drive at matched BACs (~0.067-0.068 g%) on the ascending and descending limbs.

Results: Both perceived danger and willingness to drive showed acute tolerance in the alcohol group. Participants judged driving to be significantly less dangerous and were more willing to drive on the descending limb compared to the ascending limb. The magnitude of change in perceived danger significantly predicted willingness to drive on the descending limb.

Conclusions: Decreased impairment associated with acute tolerance may lead individuals to underestimate the dangerousness of driving after drinking and in turn make poor decisions regarding driving. This study further emphasizes the descending limb as a period of increased risk and offers support for enhancing prevention efforts by targeting drivers at declining BAC levels.

Fig. 1. Differences in Perceptions of Danger of Driving across Ascending and Descending Limbs

Means for perceived danger of driving after drinking for alcohol and placebo beverage groups on the ascending (dark gray bars) and descending (light gray bars) limbs of the breath alcohol concentration curve. Larger values on the vertical axis are associated with greater perceived danger of driving after drinking (1 = “not at all dangerous” 2 = “a little dangerous” 3 = “somewhat dangerous” 4 = “extremely dangerous”). Error bars reflect standard error of the mean. Note: **p < .01; ***p < .001.

Fig. 2. Willingness to Drive across Ascending and Descending Limbs

Percentage of participants who reported willingness to drive on ascending and descending limbs of the breath alcohol concentration curve. Solid line depicts individuals in the alcohol group; dashed line depicts individuals in the placebo group. Note: ***p < .001.