Driver health and fatigue don’t correlate to truck crash risk as directly as many may think. And that may require fleets and regulators to re-evaluate how to identify “markers” for those drivers whose crash-risk profile may be higher than others.

At the 2014 Zonar Systems user conference held in San Antonio, TX, last week, Dr. Ron Knipling – a 30-year traffic safety research veteran and president of consulting firm Safety for the Long Haul Inc. – reviewed analysis of several fatigue and crash causation studies and said that fatigue is a far greater “proximal” cause in single-vehicle truck crashes compared to multi-vehicle truck-involved crashes.

He added that the various studies reviewed also indicated that typically only a small proportion of a fleet’s drivers – some 14% – were found to suffer the most “drowsy periods” when operating a commercial vehicle, with the majority of fatigue-related truck crashes occurring between 2 am and 7 am.

“Fatigue-related truck crashes mostly are single-vehicle events when the driver is alone, often on a monotonous rural road,” he said during a presentation at Zonar’s conference. “They are also very severe crashes; almost twice as severe as any other type.”

In the large truck crash causation study (LTCCS) conducted by the Federal Motor Carrier safety Administration (FMCSA) nearly 10 years ago, Knipling said the data indicated that being asleep at the wheel was the proximal cause of about 4% of the crashes analyzed, yet it jumped to 13% of the proximal cause of single-vehicle crashes, while falling to 0.4% in multi-vehicle crashes.

He also noted that a Driver Fatigue Alertness Study (DFAS) of 80 fleet drivers conducted by the Department of Transportation (DOT) in 1996 found that 14% of them suffered 54% of the all the “drowsy periods” recorded when operating their vehicles. “The study also found that one driver suffered more ‘drowsy periods’ behind the wheel than 49 of the ‘best’ drivers in the study combined,” Knipling noted.

From his perspective, “susceptibility” to fatigue is an under-appreciated issue where truck drivers are concerned, as physiological factors such as amount of sleep, circadian rhythm, time awake and general health combined with task-related factors – such as the complexity and/or monotony of the job – can make some drivers more vulnerable to fatigue than others.

Knipling noted for example when fatigue is “mapped” to truck crashes within the FMCSA’s LTCCS report, some 62% of all asleep-at-the-wheel crashes occurred between the hours of 5 am and 7 am.

He noted, too, that driver health plays a role in fatigue levels as well as a recent study by the National Institute for Occupational Safety and Health (NIOSH) found that 69% of the truck driver population is obese, 51% smoked, and few exercised regularly – with 28% of all commercial vehicle operators found to be suffering from some form of mild to severe obstructive sleep apnea (OSA).

Yet he also pointed out that the LTCCS research did not control for single versus multi-vehicle crashes in relation to fatigue as a causation factor, especially as it relates to hours of service (HOS) rules.

“The good thing about current HOS rules is that they conform to what I call ‘nature’s HOS’ which is about 16 hours,” he explained. “So that 14 hour on-duty time limit fits within that ‘natural’ HOS cycle.”

He stressed though that “time on task” does not offer a strong correlation to crash risk, as the FMCSA’s own LTCCS research found that 70% of truck-involved crashes occur within the first 5 hours of driving, with 85% of them occurring within the first 7 hours of driving.

“Thus the weakness of the current HOS rules is that they are largely unrelated to individual differences in circadian rhythm, they have no direct impact of sleep ‘hygiene’ or the ability to obtain good restorative sleep, and that there are few crashes that fall outside the HOS time constraints,” he explained.

One resource Knipling stressed for fleets to investigate in terms of helping their drivers handle fatigue better is the North American Fatigue Management Program (NAMFP) – a program the National Transportation Safety Board (NTSB) wanted to mandate for the truck industry back in August 2012.