Modest lunchtime drinking markedly worsens afternoon sleepiness in drivers

Just one lunchtime drink giving an alcohol would easily pass the breathalyser test dangerous for drivers, because of its impact natural afternoon dip in mental alertness, research in the journal “Occupational and Environmental Medicine” carried out by Research Centre at Loughborough University the direction of Professor Jim Horne.

The effect is even greater for drivers who have not slept well the night before, says the research, but unfortunately, they often don’t realise just what a detrimental effect small amounts of alcohol can have.

Around one in 10 road crashes in the UK is caused by driver sleepiness, and this rate is even higher for long stretches of monotonous driving, such as motorways.

The researchers tested the alertness of 12 young and healthy men, by getting them to drive for two hours in the afternoon in a fully functioning stationary car on a simulated motorway. They chose young men between the ages of 20 and 26, because this is the group most at risk of road crashes.

The young men’s driving skills were tested after drinking small amounts of alcohol or a non-alcoholic equivalent (although participants did not know which was which), after a night of normal sleep and after a night of disturbed sleep. The research team assessed the amount of lane drift, the participants’ subjective levels of sleepiness, and graphs of brain activity (EEG – “brain waves”).

Both the afternoon dip in alertness, caused by fluctuations in the body clock and/or a disturbed night’s sleep, and alcohol independently increased the amount of lane drift, which typified road crashes caused by driver sleepiness. These effects were also registered on the brain waves and were noted by the study participants.

But sleepiness and alcohol combined, additionally and significantly worsened the amount of lane drift. While this combined impact also registered on the brain waves drivers themselves did not seem to notice the additional effect of alcohol on their sleepiness.

The authors warn that the impact of the natural afternoon dip in alertness, even after a good night’s sleep, will be worsened by a modest alcohol intake at lunchtime at levels that would pass a roadside breathalyser test.

The research was undertaken for the Department for Transport. The Government still refuses to lower the legal drink drive limit.