We might be susceptible to sleep while in a car, bus, train, plane, or boat because of multiple factors, including the vibrations and the white noise, the sensations representative of being in the womb, the boredom, or simply the fact that we're tired.

Getting sleepy on a bus is a physiological response to a combination of low-frequency vibration, white noise, and the "Sophronic" effect. The gentle, rhythmic vibration of the bus engine and the movement of the vehicle mimic the "rocking" motion used to soothe infants, which can trigger a relaxation response in the adult brain. This is often coupled with the "white noise" of the wind and road, which masks sudden sounds and allows the brain to enter a semi-meditative state. Furthermore, many long-distance buses in 2026 have slightly elevated levels of CO2​ due to the enclosed space and recycled air, which can induce mild drowsiness. There is also a psychological component known as "highway hypnosis," where the repetitive visual field of the road causes the brain to switch into a "low-power" mode. Finally, the "forced inactivity" of a long journey provides a rare moment of stillness in a busy life, allowing the body's natural sleep debt to surface. To stay awake, experts suggest engaging in active mental tasks or ensuring you have access to fresh air from the overhead vent to keep your oxygen levels optimal.