Why Do You Feel Sleepy on Highways?
3 Answers
There are three main reasons why driving on highways tends to induce drowsiness: 1. Energy factors: High-speed driving requires intense concentration, leading to significant consumption of energy substances and oxygen by the brain. Additionally, prolonged sitting slows blood circulation, reducing the body's ability to supply energy and oxygen, which results in brain fatigue due to nutrient deficiency. 2. Oxygen factors: Drivers often keep windows closed on highways. The confined and well-sealed car space can cause a decrease in oxygen concentration and an increase in carbon dioxide levels. When CO₂ concentration exceeds 0.2% (normal level: 0.04%), it triggers headaches, drowsiness, lethargy, and difficulty concentrating. 3. Road condition factors: The enclosed highway environment has fewer distractions, higher speeds, simpler driving operations, and visually monotonous scenery. Combined with louder tire and wind noise compared to regular roads, the lack of prolonged brain stimulation creates a hypnotic effect on drivers.
I've always felt that driving on the highway makes me sleepy because the road is too monotonous. Last time I drove back to my hometown, the straight road and the identical fields and hills on both sides made my vision numb after a while. The car hummed steadily on the highway, the warm air inside was comfortable, and the seat provided good support, making me feel completely relaxed. With no lane changes or stimulation on the road, my brain easily switched to autopilot mode. I often get so sleepy after two hours that my eyelids start fighting, regretting not taking a break. To stay alert, I now listen to rock music or roll down the window for some cool air, which works decently.
From a physical perspective, high-speed driving makes drowsiness more likely. When the speed stabilizes above 100 km/h, wind and tire noise create low-frequency sounds similar to the hypnotic white noise effect, reducing brain alertness. The scenery flashes by but with low variability, providing minimal input that induces mental inertia. The uniform temperature and humidity inside the car enhance comfort but also fatigue; prolonged sitting restricts blood circulation, and muscle stiffness worsens sleepiness. I recommend stopping at service areas every 90 minutes to stretch and having snacks to replenish sugar levels and prevent drowsiness. Avoid setting the air conditioning too high—maintain a moderately cool temperature to stay alert.
