The impairing effects of alcohol intoxication and speeding on driving precision: analyses of additive and interactive effects

Automobile crash reports show that up to 40% of fatal crashes in the United States involve alcohol and that younger drivers are over-represented. Alcohol use among young drivers is associated with impulsive and risky driving behaviors, such as speeding, which could contribute to their over-representation in alcoholrelated crash statistics. Laboratory studies show that alcohol increases impulsive behaviors by impairing the drinker’s ability to inhibit inappropriate actions. This effect can be exacerbated in conflict situations where the expression and inhibition of behavior are equally motivating. The present study tested the hypothesis that this response conflict might also intensify the disruptive effects of alcohol on driving performance. Fourteen subjects performed a simulated driving task. Conflict was motivated by providing equal monetary incentives for careful behavior (e.g., slow driving) and for quick, abrupt behavior (fast driving). Subjects were tested under two alcohol doses (0.65 g/kg and a placebo) that were administered twice: when conflict was present and absent. Alcohol interacted with conflict to increase risky and impaired driving. The findings provide new insights into how alcohol might interact with personal and environmental factors that also impair driver performance and increase crash risk.