Drivers have long been urged to avoid driving while intoxicated or distracted, since doing so will drastically increase the chances of a crash. But driving while sleepy has also become a focus of more concern.

Drowsy driving occurs when someone gets behind the wheel when they haven't had enough sleep or are otherwise too tired to drive safely. A sleepy driver will not be able to focus properly, have trouble maintaining their lane or a safe following distance, and may nod off while the vehicle is still in motion. When the AAA Foundation for Traffic Safety analyzed 905 crashes between October 2010 and December 2013, it found that 9.5 percent of the drivers involved in a crash were drowsy at the time of the incident.

The Royal Melbourne Institute of Technology says drowsy driving is also prevalent in Australia, with about one in five fatal crashes in the nation involving fatigued driving. Now a recent study by RMIT University suggests that subtle vibrations in a vehicle can have a pronounced effect on increasing driver fatigue.

Researchers had 15 volunteers use a driving simulator to replicate the experience of driving along a straight, two-lane highway. The simulator's seat was placed on top of a platform that could be vibrated at different frequencies. Each volunteer completed the course once with no vibration and twice with vibrations at low frequencies.

The study concluded that the vibrations made it psychologically and physiologically harder to perform the mental tasks associated with driving. Researchers were also able to gauge a driver's drowsiness by changes in their heart rate, saying that when performing a task becomes more difficult, the heartbeat becomes more variable as the body's nervous system attempts to compensate.

"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 Stephen Robinson, a professor at RMIT University. "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."

Researchers found that volunteers became progressively drowsier as the test proceeded. Drivers began showing signs of drowsiness within 15 minutes and required substantial effort to stay alert and focused after 30 minutes.

Mohammad Fard, an associate professor at RMIT University, said more research was needed to determine how vibrations affect drivers across 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," he said. "Our research also suggests that vibrations at some frequencies may have the opposite effect and help 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.'"

Robinson said he hopes automakers can develop car seats that can disrupt the effect of low frequency vibrations and reduce the prevalence of drowsiness.

A previous study in 2015 also concluded that vibrations might increase the likelihood of drowsy driving among commercial truck drivers. The RAND Corporation looked at 24 reports on whole body vibration and found that 18 of them found a significant connection between the vibrations and fatigue or sleepiness. The study concluded that while there were several limitations to the review, reducing vibration in commercial trucks would likely reduce the frequency of trucking crashes caused by fatigue.