What makes us tired in a car if other passengers are sleeping?

April 25, 2017 - 06:20

Do sleeping people exhale or emit a special hormone that makes others sleepy?

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Do you have a long road trip in your future? Make sure that whoever sits next to you stays awake. A large percentage of people who fall asleep behind the wheel have a car full of sleeping passengers, research has shown. (Photo: Shutterstock/NTB scanpix)

One of the biggest challenges for travellers on the road is staying awake. It doesn’t seem to matter whether you are a driver or passenger, staying awake for many hours in a car can be very difficult.

One of our readers has struggled with being sleepy if her family falls asleep in the car. She may start the journey feeling awake, but when her husband and children fall asleep, she has found it difficult to stay awake.

She wonders whether it is the monotony of driving that is the cause of her sleepiness, or whether it has something more to do with the people asleep in the car.

We have asked Norway’s foremost sleep experts about this issue. Unfortunately none were aware of research on the topic.

Snoring is an advantage

Nevertheless, Professor Bjørn Bjorvatn at the University of Bergen can at least confirm one thing: There is no sleep hormone that is released through the skin or breath of sleeping people. So that is not an explanation for why you get tired when others are asleep.

But monotonous driving does make you sleepy, regardless of sleeping passengers or not, he said.

“At the same time, I think that it may well seem extra soporific if the passengers are asleep,” he said. “There might be some benefit if one or more of the passengers snore, because the snoring could keep you from falling asleep.”

Sleeping passengers a problem

Falling asleep or dozing in the car is actually a big problem, says Fridulf Sagberg, a researcher at Norway’s Institute of Transport Economics (TØI).

Ten to 20 per cent of all serious traffic accidents in Norway are caused by the driver falling asleep at the wheel.

TØI regularly conducts surveys among drivers about sleep. The replies support the observation from our reader who feels tired when she has sleeping passengers in the vehicle.

“A large percentage of those who say they have fallen asleep at the wheel have actually had passengers in the car,” says Sagberg.

But he could not explain as to why this is so.

Accidents are often serious

It is no joke to fall asleep behind the wheel.

When the Norwegian Public Roads Administration analysed all fatal road accidents between 2005-2013, it found that in about 14 per cent of all fatal accidents, there was a strong suspicion that the driver had fallen asleep.

These accidents occurred most often on a long stretch of road where the speed limit was high. This means that they can be very serious, says Sagberg.

“The consequences of falling asleep behind the wheel may be that you collide with another vehicle or drive off the road, which is the more likely possibility. If you fall asleep on a straight stretch, the car has a tendency to slowly slide toward the right,” Sagberg said.

Rumble strips save lives

Between 25 and 30 per cent of randomly selected drivers said they have fallen asleep behind the wheel at least once, according to data from TØI. Upwards of 10 per cent said they had fallen asleep behind the wheel in the last twelve months.

Most fortunately woke up before something serious happened.

The positive news in the TØI data is that more and more tired motorists are being awakened by rumble strips on the road.

An analysis by the Norwegian Public Roads Administration has shown a reduction of as much as 50 per cent in the number of those seriously injured or killed in car accidents after rumble strips were first introduced to Norway in 2008, according to an article by Teknisk Ukeblad.

Don’t drive if you’ve had a bad night’s sleep

Sagberg believes that there is just one really good piece of advice if you have to drive a long time in the car: Make sure you sleep well the night before, or preferably several nights before.

If you are sleepy while driving, stop the car and have a nap.

“Even a 15 minute nap will make you fresh and alert for several hours afterwards,” Sagberg said. Having a cup of coffee before you nap is even better, he added, because the caffeine begins to take effect just as you are waking up.

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Read the Norwegian version of this article at forskning.no

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