What causes driver fatigue?
is a factor in as many as one in six truck crashes, a new study
by the Sleep/Wake Research Centre has found.
This is more than three times higher than what was previously believed,
based on Land Transport Safety Authority (LTSA) crash reports.
Director of the Sleep/Wake Research Centre, Professor Philippa
Gander, says she has recommended that the LTSA take the lead in
a major campaign to educate truck drivers and the general public
about the dangers of driving sleepy.
"In the United States, driver fatigue is recognised as the number
one safety issue in the trucking industry,” says Professor
“You don’t have to be nodding off to be at risk,” she
says. “When you are fatigued your reaction times slow, you
don’t steer as well, your speed control deteriorates and
your cognitive functioning is impaired. This means that your ability
to assess a situation and react to it decreases.”
A 13-month study of driver fatigue in truck crashes, led by the
Sleep/Wake Research Centre and funded by the Road Safety Trust,
has now been completed.
Participation was voluntary and anonymous. To assess the biological
risk factors for fatigue, 380 questionnaires were distributed by
Commercial Vehicle Investigation Unit (CVIU) officers to drivers
involved in truck crashes in 2001-2002. CVIU officers are police
staff with advanced training in all aspects of commercial vehicle
operations and enforcement, including investigating crashes involving
In total, 146 drivers completed questionnaires. The Sleep/Wake
Research Centre then matched the questionnaires to crash reports
(minus any information identifying individual drivers) from the
LTSA crash database.
Crashes were compared for: severity; type of vehicle, service,
or load; time of day when crashes occurred; age of the drivers;
hours driven or hours on duty at the time of the crash; and hours
driven or hours on duty since the last 24-hour break.
Driver fatigue was identified in three ways. First, by the CVIU
officers ticking a box on the crash report form when they thought
driver fatigue was a factor in the crash. Second, by drivers themselves
ticking a box on the questionnaire to indicate that they thought
their own fatigue was a factor in the crash. And third, by analysing
each driver’s recent sleep and duty history, to see if they
were likely to have been affected by the biological risk factors
The key characteristics of crashes where the CVIU officer identified
driver fatigue were as follows:
• Long driving hours. Crashes where the driver had driven for at
least six hours were about three times more likely to be identified
• Long duty hours. Crashes where the driver had been on duty for
at least seven hours were about three times more likely to be identified
• Time of day of crash. Crashes between midnight and 8am were eight
times more likely to be identified as fatigue-related.
A total of 8.5 percent of crashes occurred between midnight and
8am and involved long duty hours, or long driving hours, or both.
Six drivers identified their own fatigue as a factor in their crash,
and a further three had answered “maybe”. In total,
this represents 6 percent of the drivers who answered the question.
A further five drivers considered that it was the other driver
involved in their crash who was fatigued, not themselves.
Based on previous research and the consensus of recent expert panels,
the following definitions of biological risk factors for fatigue
• Extended wakefulness. Being awake for longer than 12 hours at the
time of the crash.
• Acute sleep loss. Having less than six hours sleep in the 24 hours
prior to the crash.
• Cumulative sleep debt. At least a week since the driver had two
nights of good sleep in a row.
• Time of day. Crashing between midnight and 8am.
In total, 11 percent of drivers had at least two biological risk
factors for fatigue at the time of the crash.
Comparing the three methods for identifying driver fatigue, there
was little agreement. CVIU officers and drivers had much more information
about each crash than did the Sleep/Wake Research Centre, but were
probably not aware of the biological risk factors in most cases.
On the other hand, there may have been crashes where the truck
driver’s actions played no role, despite his/her having at
least two biological risk factors for fatigue. A total of 17.6
percent of crashes were identified (by at least one of the methods)
as involving driver fatigue. This is 3.5 times higher than indicated
by the LTSA crash reports for the study period.
As a result of the study, CVIU officers have been given advice
on the identification of the biological risk factors for fatigue.
Inspector Ian James of the CVIU says he appreciated the help. “Professor
Gander briefed staff in our four regional offices on the effects
of fatigue and how to detect it. It’s great not just to get
the latest research but also help in delivering it to the front