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Massey Magazine Issue 13 November 2002

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What causes driver fatigue?

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.

Professor Philippa GanderDirector 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 Gander.

“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 heavy vehicles.

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 for fatigue.

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 as fatigue-related.
• 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 as fatigue-related.
• 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 were used.

• 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 line staff.”

 

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