Researchers from RMIT University in Melbourne, Australia have an explanation as to why drivers become so sleepy.

They have recently found that driver fatigue is often enhanced by the natural vibrations caused by the car’s engines. These vibrations can cause people to experience symptoms of drowsiness, affecting concentration and alertness, within 15 minutes of hitting the road.

“When you’re tired, it doesn’t take much to start nodding off, and we’ve found that the gentle vibrations made by car seats as you drive can lull your brain and body,” Stephen Robinson, a professor of psychology at RMIT University and co-author of the study, said in a statement.

The study suggests that this lulling effect, while certainly not the only cause of drowsy driving, can have a significant effect on drivers’ sense of awareness, and may cause feelings of sleepiness in drivers who are perfectly awake when they step into the car.

“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,” Robinson said in a statement.

The findings could have implications for car manufacturers interested in improving vehicle safety.

Impact of drowsy driving

Every year, drowsy driving takes the lives of hundreds of drivers and passengers. According to the U.S. Department of Transportation’s National Highway Traffic Safety Administration (NHTSA), in 2016, 803 people lost their lives in accidents caused by drowsy driving, though the actual number may be far higher.

In a study involving representative sample of 14,268 crashes from 2009 to 2013, the AAA Foundation for Traffic Safety found that a drowsy driver was involved in:

• an estimated 6 percent of crashes in which a vehicle was towed from the scene;
• 7 percent of crashes in which an individual was treated for injuries sustained in the crash;
• 13 percent of crashes in which an individual was hospitalized; and
• 21 percent of crashes in which a person was killed.

If the representative data are applied nationally, the findings suggest that a drowsy driver is involved in an average of 328,000 crashes annually, including 109,000 crashes that result in injuries and 6,400 crashes that are fatal.

The study

To study the effects of car vibrations, the researchers created a virtual driving simulator mounted on a vibrating metal platform that mimics the vibrations of a car.

The simulator was designed so that the researchers could control the frequency and amplitude of the vibrations. Fifteen volunteer participants were examined as they “drove” for 60 minutes along a monotonous two-lane highway.

“While the person is driving we monitor their eye movements, steering responsiveness, and heart rate so that we can accurately determine when their ability to concentrate starts to wane,” said Robinson.

“We found that young, healthy, rested drivers start to become drowsy after exposure to 3-7 hz vibrations (i.e., 3-7 per second) within 15-30 minutes. We did not see this effect when the same drivers were not exposed to vibrations or were exposed to higher frequency vibrations.”

The researchers observed that the drivers grew increasingly drowsy over the course of the experiment, peaking after 60 minutes of driving.

The research was led by Robinson and Mohammad Fard, an associate professor at the RMIT University School of Engineering.

The study began after Fard, a vehicle engineer with years of experience managing vibration in cars, found in preliminary experiments that slower frequencies seemed to make drivers feel sleepy, said Robinson.

Safety implications

The researchers believe that their findings could be valuable for car manufacturers, who may be able to improve car designs to help reduce vibrations and keep drivers alert.

“The vibrations experienced by the driver are influenced by many factors: the road surface, speed of travel, the tyres, suspension, chassis, engine and the car seat,” said Robinson.

“Consequently, it would be difficult to modify existing cars, but it should be possible to design new ones so that vibration frequencies that cause drowsiness can be attenuated.

“There are already Industry Standards in place regarding the profile of vibrations needed for passenger comfort; now we need a similar set of standards for reducing drowsiness.”

Next step

Further research would help manufacturers figure out exactly how to reduce driver drowsiness. The research team plans to study all of the frequencies a driver may be exposed to — a range of 1 to 100 hz — and determine which frequencies are most likely to trigger feelings of sleepiness and which promote alertness.

They also intend to study the effects of vibrations on different demographics.

“We want to study a larger cohort, particularly to investigate how age may affect someone’s vulnerability to vibration-induced drowsiness as well as the impact of health problems such as sleep apnea,” Fard said in a statement.

Tip for drivers

In the meantime, drivers need to understand the seriousness of driving drowsy, and find ways to combat symptoms of fatigue on their own.

“Fatigue can have dire consequences if not managed properly,” said Robinson. “If a driver becomes aware that they are becoming drowsy and losing concentration, the safest course of action is to pull over and change drivers or take a ‘power nap.’ ”