Drowsiness and alcohol – a deadly mix for drivers
Researchers from UniSA’s Centre for Sleep Research in collaboration with the Adelaide Institute for Sleep Health (at the Repatriation General Hospital) conducted a study that compared normal sleep (8-9 hours) and no alcohol as a control condition, with the effects of sleep restriction to four hours alone, and in combination with low and legal doses (0.025 and 0.035g/dL) of alcohol on young, fit adult men aged 18 to 30 years.
Men in this age group were chosen because they are the most over-represented group in motor vehicle crashes, according to research fellow, Dr Stuart Baulk.
“In each of the four conditions, the participants operated a driving simulator for 70 minutes non-stop, starting at 2pm. This time was chosen because we know that people often feel drowsy in the early afternoon as well as in the early hours of the morning when their body clock is at its lowest,” Dr Baulk said.
Tiredness levels were chosen to represent realistic conditions, rather than subjecting participants to excessive sleep restrictions for abnormally long amounts of time.
Honours student researcher Andrew Vakulin used the simulator to measure drivers’ steering deviations, number of crashes and reaction times, and prompt them at regular intervals to rate themselves between one and nine on what they considered their level of drowsiness to be and how well they thought they were driving. Lastly, they had to make a decision on whether they should stop driving or keep going. In addition, their faces were videotaped for visual clues and electrodes were used to measure changes in brainwaves.
While alcohol and its effects are well documented and many people strongly oppose drink driving, driver sleepiness is more acceptable to the general public, despite being the cause of about 20 per cent of motor vehicle crashes each year.
“A UK driver who fell asleep at the wheel in February 2001 veered off the road and collided with a train that derailed into the path of another train, causing 10 deaths and many injuries, and was jailed for five years for negligent driving,” Dr Baulk said.
“That should be a wake-up call for sleepy drivers as crashes like this could easily happen to them,” he said.
But Dr Baulk believes that mixing alcohol (particularly towards the legal limit of 0.05) with sleepiness should be of even greater concern.
“Our study showed that while there were differences between each of the four driving conditions, the higher alcohol level really stood out. Participants knew that their driving had become significantly affected by deviations in performance levels and tiredness, and they rated themselves accordingly. After just half an hour their driving was impaired, with more deviations the longer they drove, especially in the last 20 minutes when there was even greater separation between drivers and the road. We believe that if the driving had been extended to two hours, the results would have shown an even more rapid deterioration in driving performance.
“These results should be setting off alarm bells for tired drivers who drink alcohol,” Dr Baulk said. “The combined effect of alcohol consumption mixed with sleepiness puts drivers at much greater risk of accidents and death by dangerous driving than sleepiness alone,” he said.
“The main purpose of this research has been to back that up with scientific evidence and to educate people to pay attention to their levels of sleepiness, realise their limitations and manage their alcohol intake to minimise risk. Minimising risk means not trying to be just under the legal alcohol limit at 0.049g/dL,” Dr Baulk said.
“It’s really important to understand that the three factors together - sleep loss, alcohol and driving at mid afternoon or early morning - magnify driving risk. If we can manage these risks by having regular breaks, plenty of sleep, and avoiding alcohol in the middle of the day, incidents could be avoided.”
Dr Baulk supervised Andrew Vakulin’s honours research project, funded by the Australian Brewers Foundation, and is now conducting further research in this area funded by the NHMRC. Vakulin is continuing this work for his PhD, looking at these issues in people with sleep apnoea.