Interactions Between Sleepiness and Moderate Alcohol Intake in Drivers

This report summarises the result of a three-year study into the interaction between sleepiness and moderate alcohol intake.

Both alcohol and sleepiness are known to be major contributors to road traffic accidents in the UK. There has been much debate on whether the current legal breath alcohol concentration (BrAC) limit for driving (35g alcohol per 100ml breath) should be lower, as it is in several other countries in the European Union. The present limit may be satisfactory when a driver is fully alert, however the pressures of today’s society mean that an increasing number of people may be sleep deprived. The consequences of a sleepy person driving after drinking a currently legally acceptable amount of alcohol have not been fully investigated. This report describes the result of a three-year study into the interaction of sleepiness and moderate alcohol intake.

An initial literature review identified specific areas that needed to be investigated.
Our research takes a ‘lifelike’ scenario, with only moderate sleep restriction (five hours in bed at night) and moderate alcohol consumption, producing BrACs of approximately half the UK legal driving limit. The drive, on a simulated dual carriageway, lasted for two hours and was very monotonous.

The research programme was split into four main areas:
1. Young men (most at risk group of drivers for sleep-related crashes) driving in the afternoon (when sleep-related crashes increase), under a 2 3 2 experimental design (with and without alcohol at lunchtime) and (with and without prior sleep restricted to five hours);

2. An identical comparison with young women;

3. A time-of-day comparison with young men, and driving and alcohol consumption taking place in the early evening (a time of day when we are naturally more alert); and

4. A near-zero BrAC before starting the afternoon,when young men have the
same alcohol intake as in (1) but earlier.