New research into driver fatigue reveals why we fall asleep at the wheel

Even more disconcerting than the fact that almost one in three drivers (29 per cent) in Australia have knowingly driven while drowsy is the statistic that tells us 20 per cent have actually reported nodding off at the wheel. This means one in five drivers have fallen asleep whilst driving a car on the road they are sharing with other cars containing mums and dads, brothers and sisters, babies and toddlers, as well as pedestrians.

A great deal of research has been conducted around this issue, mostly focusing on external solutions – rumble strips on the road, driver awareness campaigns, signage and roadside rest stops and so on.

Research has found that car vibrations make people sleepier, affecting concentration and alertness levels.

More recently, researchers from RMIT University’s School of Engineering, guided by Associate Professor Mohammad Fard and Professor Stephen Robinson, have attempted to solve the problem from a different angle. They are analysing the effects of physical vibration on heart rate as a measure of driver drowsiness.

The results of the study, the investigators believe, could guide car seat designers and manufacturers to a previously unconsidered solution.

Rock-a-bye, baby…

In order to find out whether adult drivers are easily rocked to sleep by the movement of their carriages, the research team set up an experiment that would look at the relationship between physical vibration and drowsiness from two unique angles.

One was the measure of heart rate variability (HRV), which indicates increased mental workload, leading to stress and tiredness. This offered an objective point of view that was independent of anything voluntarily reported by the subjects in the experiment.

The other involved the use of the Karolina Sleepiness Scale (KSS), the most widely used subjective measure of sleepiness. The KSS involves the subject self-reporting their level of drowsiness. Data from both measures would be compared to ensure the veracity of the study’s results.

Then came the engineering part of the experiment, which involved the construction of a test rig that would best replicate the experience of driving on a road. In doing so, the research team would discover whether the bassinet in which adult drivers are rocked to sleep is, indeed, the family car.

Building a driving simulator

The test rig consisted of a driving simulator built around a mid-sized sedan car seat, on a platform that served as a vibration table. That platform was anchored to the ground by air mounts and a hydraulic actuator below its centre provided the movement.

A computer gave and recorded feedback to the steering wheel and imagery to a 32-inch monitor placed in front of the driver, which played driving simulation footage of a high speed yet monotonous journey on a motorway.

Test performed on the virtual simulator.

Each driver controlled the ‘vehicle’ for 60 minutes, wearing ear muffs to cancel out environmental noise.A control group did the simulated drive with no vibrations, while another group drove with vibrations in the 4-7 Hz frequency band – corresponding to the frequency band of brain waves associated with driving and drowsiness.

The results were astounding.

How to make our roads safer

“Our study shows steady vibrations at low frequencies - the kind we experience when driving cars and trucks - progressively induce sleepiness even among people who are well rested and healthy,” said Professor Stephen Robinson.

“From 15 minutes of getting in the car, drowsiness has already begun to take hold. In half an hour, it’s making a significant impact on your ability to stay concentrated and alert.”

During each individual’s 60-minute drive, sleepiness increased dramatically amongst those in the test group that experienced the vibrations. As Professor Robinson reported, it took just 15 minutes for signs of drowsiness to reveal themselves and after 30 minutes, a noticeable effort was required for the driver to operate the vehicle in a safe manner.

Prof Stephen Robinson and A/Prof Mohammad Fard.
Professor Stephen Robinson and Associate Professor Mohammad Fard.

The group not subjected to vibrations also became increasingly tired during the experiment but to a significantly lesser extent.

“These findings add further weight to our published reports on the role of low-frequency vibration in inducing drowsiness,” the report said. “The findings of this study will need to be replicated and extended to other frequency bands in the 1–15 Hz range … These findings are likely to have significant implications for road safety and vehicle design.”

In a fascinating twist, Professor Fard says certain frequencies of vibrations might actually help to keep people awake. “So we also want to examine a wider range of frequencies, to inform car designs that could potentially harness those ‘good vibrations’,” he said.

To improve road safety, car seat designers must keep these research results in mind, Professor Robinson said. They must innovate to develop features that disrupt specific vibrations being delivered from the road and the engine to the driver. In doing so, they will help to keep drivers awake and will, therefore, save lives.

Learn more

The project brought together a number of disciplines including engineering, sleep psychology and virtual reality from across RMIT. The School of Engineering is driving cutting-edge research in its field and offers courses in engineering management online and on-campus.