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.

Humans often find it easier to fall asleep and stay asleep on a train due to a combination of low-frequency vibration and white noise. The rhythmic "clack-clack" of the wheels and the gentle, side-to-side rocking motion (often called "rocking the cradle") mimic the vestibular stimulation that infants experience, which has a naturally soothing effect on the human nervous system. Scientific studies have shown that these gentle oscillations can synchronize brain waves, encouraging the transition into N2 and N3 deep sleep stages. Furthermore, the constant "hum" of the train acts as white noise, masking sudden external sounds that might otherwise wake a sleeper. Psychologically, being on a train often removes the "pressure of choice"; once you are on board, there is nothing else you can do but wait, which allows the mind to relax and surrender to fatigue. In 2026, many luxury night trains are designed with specific suspension systems to enhance this "resonant sleep" effect, making rail travel one of the most restorative ways to move between distant cities.