Your car might be trying to kill you by lulling you with sleep-inducing vibrations

Perhaps as many as a quarter of a million people die in vehicle collisions every year worldwide due to driver fatigue. Now Australian scientists say the vibrations from your car on long drives could be lulling you to sleep.  

Fatigue is behind 20 per cent of fatal collisions, according to Transport Canada's website. The researchers have discovered that part of the reason drivers get so drowsy is that cars can produce sleep-inducing vibrations. 

Harmful vibrations

Prof. Stephen Robinson at the Royal Melbourne Institute of Technology (RMIT) and his team found steady vibrations at low frequencies — the kind we experience when driving cars and trucks  — lull the brain and body. 

In a recent issue of the journal Ergonomics, they showed car seat vibrations are tied to drivers' struggles to stay alert enough to perform a simple driving task in a simulator.

• Research Paper in Ergonomics

"We believe that what's happening is that the sensory input that's coming from the vibrations is starting to synchronize the brain waves and put the brain into sleep," said Robinson, head of the psychology department at RMIT.

Coincidentally, he said, the frequency of car seat vibrations closely matched those of theta waves. Theta waves are a type of brain wave connected with entering the sleep state.  EEGs show that as subjects drift off to sleep, theta wave activity increases. 

To investigate this, Robinson and his engineering colleagues used a mock-up of a car seat on a massive, stainless steel platform. Drivers used a steering wheel to control a virtual vehicle and travel on a road displayed on a screen in front of them.

Stay on the road

The researchers vibrated the seat at a variety of low frequencies resembling what we normally experience when driving — a range of 4 to 7 Hertz — and without vibrations.  

They were particularly interested in these frequencies because previously, Japanese researchers found train passengers who experienced whole body vibrations also reported being more tired and zoning out.

The 15 volunteers (four women and 11 men) simulated drives down long, straight, boring roads — a worst-case scenario for nodding off behind the wheel. 

The volunteers were about 23 years old.  They weren't sleep deprived, and they headed to the simulator after a regular day at school or work for an hour-long test. Their only task was to stay on the road. 

But scientists say the tiredness brought on by vibrations makes it both psychologically and physiologically harder to perform all the tasks we need to do to drive safely. 

We believe that what's happening is that the sensory input that's coming from the vibrations is starting to synchronize the brain waves and put the brain into sleep.- Prof. Stephen Robinson

To learn more, the researchers used eye trackers to measure how our eyes can drift off the road. They also watched for drooping eye lids.

"The car typically does an S shape all the way up the road as we get very tired," said Robinson. 

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The team also measured heart rate changes, which Robinson called a sensitive measure. The body's nervous system gears up to compensate for tiredness, leading to telltale changes in the heart rate.

15-minute effect

In the experiment, just 15 to 30 minutes of vibrations put the drivers at a high risk of a crash, based on their heart rate responses.

"That really surprised us," he told CBC Quirks & Quarks summer host Britt Wray. "We didn't expect to see such a rapid effect." 

The volunteers also admitted on questionnaires that they had trouble staying awake. 

Since the participants were randomized to vibrations or no vibrations on different days, the scientists could tell that the effect was from the shaking itself.

Harness good vibrations 

The findings also point to ways to keep drivers safer. 

One idea is to to add materials in the car seat to absorb harmful vibrations. Another idea is perhaps to add cancelling counter-vibrations, similar to the way noise cancelling headphones work. While the researchers say there are already ways to dampen vibrations in cars, Robinson aims to check the impact of other frequencies before approaching car makers and insurers about adding the feature.  

Increasing "good vibrations" might be another option. Robinson said his unpublished, early data suggests there are also vibrations that enhance our alertness. 

Anecdotally, Robinson said drivers have reported feeling less tired driving the same route with one vehicle compared with another. For now, he suggested, if anyone is having trouble, try switching vehicles to see if it helps. 

Factors that influence the vibrations we feel on the road include:

• A vehicle's tires and suspension.
• Car seat design.
• Engine vibration.
• Road surface.
• Speed.

Another tip? Lay off the cruise control for a bit if you're travelling on the same road surface for a long stretch. "There may be an advantage to changing your speed every so often." 

And for parents valiantly trying to get a cranky infant to sleep, the findings lend support for short drives to take full advantage of lullaby vibes.