Bus Rides And Sleep: Why Do I Nod Off?

There are many reasons why bus rides might make you feel sleepy. One of the most common reasons is the monotony of the journey. The repetitive scenery, the dullness of the journey, and the lack of stimulation can cause your mind to switch off and make you feel tired. The comfortable seats, the gentle rocking motion, and the white noise of the engine can also contribute to sleepiness. Additionally, the vibration of the bus can stimulate the parasympathetic nervous system, inducing relaxation and drowsiness. If you're already sleep-deprived, the inactivity and comfort of a bus ride can be the perfect opportunity for your body to catch up on some much-needed rest.

Comfortable seats and ventilation systems

The design of the seats on public transport is such that they provide a reasonable level of comfort for passengers. While they may not be as plush as your sofa or mattress at home, they are built to be cosy enough for short naps or longer journeys. The ability to sit, close your eyes, and lean your head against the seat back can be enough to send you into a relaxed state, especially if you're already feeling sleepy.

Additionally, the ventilation systems on buses and trains are designed to keep the interior temperature comfortable for passengers. A warm environment can induce sleepiness, as mammalian bodies cool down during certain phases of the circadian cycle. The energy expended to regulate body temperature can contribute to feelings of drowsiness. Well-regulated ventilation systems ensure that the temperature remains pleasant, reducing one factor that might otherwise keep you awake.

The combination of comfortable seating and a well-maintained temperature can make public transportation an ideal environment for catching up on some sleep. It's no surprise that many people find themselves dozing off during their commute or even during longer journeys.

Furthermore, the sense of security and safety that comes with riding buses and trains can also contribute to the sleepiness. Passengers generally trust that the drivers are skilled and experienced, allowing them to relax and let go of any travel-related anxieties. This sense of security can further enhance the sleep-inducing effects of the comfortable seats and pleasant temperature maintained by the ventilation system.

Long periods of inactivity

This inactivity also slows down your brain activity because there's no stimulus to keep it awake. Rides are relatively monotonous. For minutes or hours, you stay in the same position, looking at the repetitive things around you: trees, houses, streetlights, road lines, and pavement. Naturally, your mind gets tired of this pattern, leading to what is known as "highway hypnosis."

Highway hypnosis is a trance-like state that people can experience when riding in a car for long stretches of time. Repetition and high predictability are the big factors for highway hypnosis, causing our attentiveness to plunge. Our brain just gets used to the things we see on the road, and it all starts to feel automatic. This leads to sleepiness, and before you know it, you're snoozing.

White noise

The uniformity and consistency of white noise can also help to relax the mind and body. The lack of variation in the sound creates a sense of monotony, which can be soothing and help to slow down brain activity. This monotony may also contribute to sleepiness, especially if you are already tired or sleep-deprived.

Additionally, if you are accustomed to falling asleep with white noise in your bedroom, hearing similar engine noises during a bus ride may trigger a conditioned response. Your brain may associate these engine sounds with sleep, making you feel sleepy. This is similar to how certain scents or songs can evoke specific memories or emotions.

It is worth noting that while white noise can be beneficial for sleep, excessive noise or prolonged exposure to loud noise can have negative effects. It is important to be mindful of the volume and duration of white noise usage to avoid any potential hearing damage. Overall, white noise can be a useful tool for improving sleep quality, especially when traveling or in noisy environments, but it should be used in a safe and controlled manner.

Rocking motion

The rocking motion of a bus is similar to the motion that lulled us to sleep as babies. Joanne Getsy, Drexel University Sleep Center Director, calls this the "womb-like effect", which makes us feel safe and comfortable.

Jade Wu, Ph.D., a psychologist, Sleep.com sleep advisor, and board-certified behavioral sleep medicine specialist, explains that fetuses experience whole-body low-frequency vibrations all the time in the uterus from the mother’s movements, heartbeat, and other bodily functions. This is why rocking and gently bouncing can soothe newborns to sleep. It is thought that adults retain some of the association between rocking and drowsiness.

A small 2017 study found that within 15 minutes of exposure to low-frequency vibrations, participants became drowsy. This may be because low-frequency vibrations can stimulate the parasympathetic nervous system, which is the "rest-and-digest" system that can induce relaxation and sleepiness.

The monotony of the passing landscape, the comfortable seats, the white noise of the engine, and the temperature-controlled environment of a bus may also contribute to sleepiness.

Carbon dioxide levels

Carbon dioxide (CO2) concentrations in tour bus cabins are higher than outdoor concentrations because humans produce and exhale CO2. While CO2 has direct health effects on humans, these are observed at concentrations of 20,000–250,000 ppm, much higher than those found in normal indoor settings. However, at levels exceeding 600 ppm, occupants may experience specific adverse health effects such as headache, drowsiness, difficulty concentrating, dizziness, eye irritation, and fatigue.

Several studies have examined CO2 concentrations in various types of vehicles, including tour buses, and found that they typically exceed 1000 ppm, which can cause drowsiness and fatigue in drivers. For example, a study of CO2 concentrations in a bus in Hong Kong found levels of 1900 ppm when travelling on the highway and 2500 ppm in the city. Another study of long-distance buses in Taiwan reported average onboard CO2 concentrations ranging from 339 to 3722 ppm, with an hourly average of 959 ppm.

A particular study investigated CO2 concentrations in 43-seat tour buses during a three-day, two-night school excursion. The results showed that both the driver and passenger zones of the buses reached maximum CO2 concentrations of over 3000 ppm, with daily average concentrations of 2510.6 and 2646.9 ppm, respectively. These findings exceeded the indoor air quality standards set by the Taiwan Environmental Protection Administration (1000 ppm for 8 hours) and the Hong Kong Environmental Protection Department (2500 ppm for 1 hour).

The high CO2 concentrations in tour bus cabins are attributed to several factors, including the number of passengers onboard, lower driving speeds, and the use of air conditioning systems in recirculation mode, which reduces ventilation and contributes to stagnant air.

To improve air quality and mitigate the potential health impacts of elevated CO2 levels, it is recommended to increase the ventilation frequency in tour bus cabins during journeys. Additionally, tour bus drivers are encouraged to open the bus doors and windows when passengers disembark and the bus is on standby.

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