Everyone kinda likes a vibrating chair. Whether it’s the coin-operated kind at the mall or airport, or the ones that replace a masseuse at cheap spas, vibrating chairs are always a bit awkward but ultimately relaxing because our bodies like to be shaken gently. Like babies in cradles, we’re soothed by peaceful, repetitive movement. This is great when it’s intentional, but not when the vibrations come from a car, researchers warn in a new study in the journal Ergonomics.
That’s because the last thing you want to do in a car is become drowsier than you already are, write the team of RMIT University psychologists in the paper, published this month. Drowsy drivers are involved of 9.5 percent of all crashes — up to 10.8 percent in severe ones — reported researchers in a study published by the AAA Foundation for Traffic Safety in February. And according to the new paper, co-authored by RMIT psychology professor Stephen Robinson, Ph.D., the vibrations of cars might only make that drowsiness worse — but you already knew that.
“[At] an intuitive level, we are all aware that there must be a link - that is why parents sometimes drive their children in a car to help them go to sleep,” Robinson told Inverse in an email. What he and his colleagues wanted to do in the new study is measure the effect of car vibration on driver heart rate so they could better understand its link to drowsiness and design interventions to keep people awake.
They performed their experiments on 15 Australian drivers inside a virtual simulator meant to mimc what it’s like to drive on a monotonous two-lane highway, set up on top of a platform that could vibrate at low frequencies of four to seven Hertz (cycles per second). By monitoring heart rate during the simulations, the team found that it only took 15 minutes of vibing and driving before drowsiness sets in, and after half an hour, it started to affect the ability to stay focused and alert, noted Robinson in a statement published July 5. Drivers who know they are getting sleepy are in a stressful position, they explain, and the the stress of trying to stay awake manifests as increased variability in heart rate.
These findings are consistent with the team’s previous work and a handful of Japanese studies, like one 2017 Journal of Healthcare Engineering paper, showing that vibrating trains make passengers sleepy. But, perhaps worryingly, “relatively little attention has been given to the link between vehicle vibration and drowsiness,” says Robinson.
But the more we can learn how vehicle vibrations affect drivers and which ones are most sleepiness-inducing, the easier it’ll be to design a way to intervene. Robinson explains that controlling car vibrations is a twofold process that requires limiting those from both the surface of the road and those from the engine. “Motor vehicle manufacturers already have methods of passively limiting vibrations from these sources to improve passenger comfort,” he says.
It’s possible to actively cancel out “bad” vibrations in the same way that noise-cancelling headphones block out unwanted noise with benign sounds through vehicle and seat design, he says, but “we will first need to determine in greater detail the exact frequencies that are problematic.”
Not all vibrations, after all, make you want to go to sleep. The trick to solving the drowsiness issue will be figuring out which frequencies are most problematic — and, possibly, finding the one that might keep drivers awake.
“We do not have a definitive answer, as we are still researching this,” says Robinson. “Our early pilot data suggests that 20 Hz (20 vibrations per second) may help drivers to stay alert, but this may change when we have collected more data.”
In the meantime, drowsy drivers should remain aware of their mental state — and pull over when it gets to be problematic. “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’,” Robinson says.