Alcohol intoxication progressively impairs drivers' capacity to detect important environmental stimuli.

RATIONALE: Alcohol intoxication impairs driving skills, leading to an increased frequency of accidents and crash fatalities. Inebriation may specifically impair environmental vigilance, reducing the driver's capacity for attention to stimuli that are relevant to successful navigation.

OBJECTIVES: We examined the separate and interactive effects of breath alcohol concentration (BrAC) and simulated driving scenario on the capacity to correctly identify visual stimuli embedded in the environment.

METHODS: Ten healthy young adult drivers (6 males; 4 females) each performed 4 driving scenarios at each of 3 steady breath alcohol concentration levels (0, 60 and 100 mg/dl). Scenarios were based on speed or distance keeping while navigating a rural 2-lane road in daytime or nighttime conditions. Drivers pressed a button on the steering wheel corresponding to the direction of an arrow (up or down) which appeared briefly on road signs embedded in the environment, either overhead or on the roadside.

RESULTS: Increasing level of BrAC and subjective scenario difficulty manifested significant, separate, but not interactive influences in association with the number of arrows correctly identified. Significant impairments could be detected at a level of BrAC below the current American limit for legal operation of a motor vehicle.

CONCLUSIONS: Environmental vigilance is subject to impairment by either/both alcohol intoxication and driving conditions.