Led by Andrew Vakulin, of the Adelaide Institute for Sleep Health at Repatriation General Hospital in Australia, the study was published in the October 1 issue of the journal Sleep.
The research enrolled 21 healthy young men, aged 18-30 years, who all had normal sleep patterns and no sleep disorders.
Participants had to perform an exercise as part of the research wherein they completed a 70-minute simulated driving session, which included steering deviation, braking reaction time, and number of collisions, and underwent repeated measures with four experimental conditions: normal sleep without alcohol, sleep restriction alone (four hours) and sleep restriction in combination with two different low BACs (0.025 g/dL and 0.035 g/dL).
The findings of the research revealed that steering deviation increased significantly when sleep restriction was combined with the higher dose alcohol. This combination also resulted in a greater subjective sleepiness and negative driving performance ratings compared to control or sleep restriction alone.
"The ability to keep the car in the middle of the lane is critical to safe driving, and is one of the more sensitive measures of driving impairment," Vakulin said.
"Although steering deviation was not significantly affected by sleep restriction alone, alcohol at a BAC as low as 0.025 g/dL in combination with sleep restriction was sufficient to significantly impair steering ability. This combination may considerably reduce the threshold for safe driving, as suggested by the steering deviation data and an increase in off-road collisions following sleep restriction and alcohol ingestion in this study," he added.