Is Your Truck Putting You to Sleep?

A ground-breaking bit of research from Australia has shown that low-frequency vibrations can make drivers drowsy. If this is true and research is proven conclusive, it will call into question just about all we assume about truck crashes where the driver apparently fell asleep at the wheel. Those drivers may in fact have been very drowsy but may not have been "fatigued" in an hours-of-service context, the way that term is typically applied to "tired drivers."

A recent installment of the Canadian Broadcasting Corporation (CBC) radio program "Quirks and Quarks" featured an interview with Australian researcher, Prof. Stephen Robinson, head of the psychology department at the Royal Melbourne Institute of Technology (RMIT). Robinson and his team found that low-frequency vibrations (usually in the range of 4-7 hertz or cycles per second) coming up through the floor of a car and through the seat are causing driver drowsiness. They are lulling drivers into a state of inattentiveness, or "zoning out" as some might describe it.

Testing the team did using 15 volunteers (four women and eleven men in their early twenties) found that subjects became drowsy and at higher risk of a crash after exposure to the low-frequency vibrations for as little as 15 to 30 minutes. The subjects weren't sleep deprived, either. They attended the testing sessions after a regular day at school or work. The subjects were tested twice in randomized vibration and no-vibration simulations. Their only task was to stay on the road during a driving simulation exercise.

"We noticed that the vibration-induced drowsiness can be detected statistically after between 15 to 30 minutes of exposure," Robinson told Quirks & Quarks summer host, Britt Wray. "That really surprised us. We didn't expect to see such a rapid effect."

The test consisted of a driving simulator with a seat, steering wheel and computer monitor displaying a road in front of the subject. The whole rig was mounted on a massive steel plate that was set up to mimic the amplitude and frequency of vibrations experienced in a real car driving on a real road.

Observers could visually detect when the subjects were starting to become drowsy by a decline in their lane tracking ability. Subjects were also observed with an eye-tracking device that detects drooping eyelids, and there was a firm correlation between the drooping eyelids and poor lane tracking. But perhaps most convincing was data from a heart rate monitor and an electroencephalogram (EEG) that monitored brain activity.

"We have various brain waves that can be recorded by EEG, and as we move from alertness into the first stages of sleep, or brain waves slow down," said Prof. Robinson. "We believe the sensory input that's coming from the vibrations starts to synchronize the brain waves and put the brain into sleep."

The heart-rate monitor showed a similar correlation.   

"When you start to fight tiredness, there's a particular pattern of variability in the heart rate related to the effort it takes to stay awake," he noted. "We were looking for that signature. We also looked at steering wheel entropy, which is the ability to make small steering corrections while driving. We get slower at doing that as we become drowsy."

The Quirks & Quarks webpage related to this story also notes additional research published in the September 2017 issue of the journal, Ergonomics, that shows seat vibrations can be tied to drowsiness. The introduction to the paper states: "Driving a motor vehicle requires sustained mental workload and attention, consequently drowsiness and impaired alertness can compromise situational awareness and driving performance. There is a growing body of evidence, including our reported findings, that whole-body vibration may be an important inducer of driver drowsiness."

Implications for Trucking

Note the use of the term drowsiness in the previous sentence. The authors did not use the term fatigue or fatigued, as surely would be the case if someone was describing the likely cause of a truck crash where the driver had driven off the road or into a lineup of stopped vehicles.

You can call it semantics if you want, but I think there's a huge difference between the terms drowsy and fatigued, especially in how they are applied in the context of a truck crash. Fatigued implies the driver was tired. If you want to take it a step further, by inference it implies there might be an hours-of-service compliance problem. If the driver had taken their required rest breaks, how could they be so tired as to fall asleep at the wheel? 

Unfortunately, the term "fatigue-related crash" is convenient and it fits nicely with the ELD/HOS narrative that safety advocates and regulators use constantly.

Well, what if the driver isn't fatigued at all, is totally compliant with HOS, but was lulled into a state of inattentiveness by the road and the truck? Today's trucks are pretty luxurious, with their deeply padded seats, noise-reducing upholstery, almost hands-off operation, etc. The driver doesn't have a lot to do anymore that demands some interaction with the vehicle, like shifting gears. Without some stimulation to keep drivers alert or some way of overcoming the low-frequency vibrations studied by the Australian researchers, how likely is it that drivers are being lulled to sleep by their trucks but are being hung out to dry on a fatigue-related violation?

It's interesting that in the aftermath of a truck crash, the media often report that "it appeared that the driver fell asleep at the wheel." I wonder how often the post-crash investigation reveals a totally compliant driver. We never hear about the results of those investigations in the news.

On April 10, 2014, a truck driving on Interstate 5 near Orland, California crossed a 58-foot-wide median and crashed onto a motorcoach traveling in the opposite direction. Investigators from the National Transportation Safety Board found no significant mechanical problems with the remains of the truck; certainly nothing that could be attributed as a causal factor.

On the human side, NTSB investigators were unable to determine why the truck crossed the median, but they ruled out truck and motorcoach driver experience, licensing and training, as well as alcohol and drug use, and weather as causes of the crash. Likewise, the agency found no evidence that the driver was experiencing distraction, fatigue, or that he intentionally crossed into opposing traffic.

What if low-frequency vibration from the truck had simply lulled the driver into a state of inattentiveness, just like the subjects of Prof. Robinson simulations at RMIT?

The NTSB normally doesn't get involved in truck crashes except those of a spectacular nature or with a high number of fatalities -- 10 died in this particular crash. That agency digs deep into the causes of a crash and it's particularly telling when even NTSB cannot come up with a smoking gun. Now consider the average police investigation of a crash, nowhere near as thorough as an NTSB investigation. If the crash looks like a "fatigue-related" crash with the usual tell-tale signs of no evasive action, no brake skid marks etc., it would probably be reported as such.

I have experienced those lulls in attention, usually driving on straight, flat familiar roads with a steady rumble coming from the engine and the tires. They were as likely to occur two or three hours into a shift on a bright sunny morning as around mid-afternoon, during a typical low-point in my circadian cycle. I'm pretty sure most drivers could say the same thing. We probably all took the same preventive measures at the onset of the drowsiness, like opening a window or cranking up the radio. But what if, as Prof. Robinson's research seems to suggest, there's a physiological link between the frequency of the vibrations we get from the truck and the cadence of certain brain waves? Our trucks might be literally putting us to sleep.

A couple of things about Prof. Robinson's revelations worry me: Drivers under the time pressure of an ELD might be disinclined to stop or try to do something to break the cycle of the vibration-induced drowsiness, which could lead to increased crash risk. The other is the implications for platooning. If low-frequency vibrations are already causing drowsiness, what do you think might happen when you run trucks down the road so close together that the following drivers have little forward visual stimulation to keep them alert?

I know truck makers are aware of the implications of low-frequency vibration as it's often cited to as a likely cause of back and leg problems in drivers. I'd say, if Robinson's suppositions are accurate, there's a much more pressing need to address this issue. Maybe we need to think about making trucks less cloud-like to drive, and a little more like the rough and tumble trucks of yore. At least they kept us awake.