COMMENT: Driving laps around the neighbourhood at 4am is a technique many parents have used to help their restless baby fall asleep.
Now scientists believe they might understand how cars can make us drowsy and their research shows it's not just limited to babies.
Head out on any long road trip with children in the back, and the chances are they will fall asleep for some of it. Previous research has found the low frequency vibrations produced by trains can make their passengers more sleepy. So scientists in Australia decided to see whether car vibrations could make its occupants more likely to nod off too.
They took 15 healthy young adults who had slept for more than seven hours for the previous five nights and asked them to drive a virtual car simulator. Given the nature of the experiment it was determined too dangerous to test this theory with a real car on the road.
The simulator was designed to replicate the experience of driving on a long road trip with little visual scenery, traffic or stops provided on a two lane highway. With low light conditions and no distracting sounds, the tests were conducted between 10pm and 2am, around an hour before the volunteers' usual sleeping time.
During the first driving experience, the driver's car seat produced vibrations at low frequencies between 4 and 7 Hz. These were set up to be similar to those experienced in a real car, caused by vibrations transferred from the surface of the road and the car's engine.
The second driving experience did not involve any seat vibration during the 60-minute drive time, however all other parameters were kept the same. The driver's heart rate was monitored throughout the tests and they were asked to rate their level of tiredness.
Even though the volunteers were well rested and healthy, they started to experience drowsiness within 15 minutes of driving the car with the vibrating seat.
Within 30 minutes the vibrations had a significant impact on the ability of the drivers to stay concentrated and alert, with their drowsiness peaking after 60 minutes of driving - which is when the experiment ended.
In New Zealand, driving while feeling tired is common. A study by the Automobile Association found one in five New Zealanders said they had momentarily fallen asleep at the wheel. The consequences of this can be deadly, with 9 per cent of all fatal crashes in New Zealand last year caused by tired drivers.
Although the reason why low frequency vibrations cause drowsiness is still unclear, it has been suggested the brain might become synchronised to the vibrations emitted by cars causing it to enter an early stage of sleep.
Vibration is not the only sleep-inducing output of a car; other research has shown sustained white noise such as that produced by car road noise can also induce drowsiness.
Although a negative combination for those of us driving long distances, this sleep-inducing research is being put to good use by the baby industry.
Car-mimicking cots are now available for a more environmentally friendly solution to getting your baby to sleep. With a vibrating mattress designed to simulate the soothing movement of a car ride, a built in audio system to play an engine soundtrack as background noise and integrated microphones that start the process when it hears the baby wake up, technology filled cribs are in the marketplace.
Although further research into fatigue-inducing car vibration is still needed, this research suggests vibration-cancelling driver seats might be the next safety innovation for the automotive industry.