很多人在乘坐高铁时容易感到困倦，常有人猜测这是因为车厢内二氧化碳（CO₂）浓度过高所致。实际上，高铁车厢是密闭但高度通风的环境，现代高铁普遍配备先进的空调与新风系统，能有效控制二氧化碳浓度，通常维持在1000 ppm（百万分之一）以下，远低于引发明显困倦的阈值（一般认为2000 ppm以上才可能影响警觉性）。因此，单纯将犯困归因于二氧化碳超标并不准确。更可能的原因包括：旅途中的单调视觉刺激（如窗外快速掠过的风景）、稳定的白噪音（如车轮与轨道的摩擦声）、舒适的座椅和恒温环境，这些因素共同作用会诱发“旅途性嗜睡”。此外，人体生物钟、睡眠不足或饭后乘车也会加剧困意。当然，在极端高峰时段，若车厢严重超员且通风系统负荷过大，局部区域二氧化碳浓度可能短暂升高，但这种情况较为罕见，且高铁运营方会通过调节新风量来应对。因此，坐高铁犯困更多是多重生理与环境因素综合作用的结果，而非单纯的二氧化碳超标。
Many people feel drowsy when riding high-speed trains, and some often suspect it’s due to elevated carbon dioxide (CO₂) levels inside the cabin. In reality, high-speed train carriages are sealed yet highly ventilated environments. Modern trains are equipped with advanced air conditioning and fresh-air systems that effectively maintain CO₂ concentrations—typically below 1000 parts per million (ppm), well under the threshold (usually above 2000 ppm) at which noticeable drowsiness or reduced alertness might occur. Therefore, attributing sleepiness solely to excessive CO₂ is inaccurate.More likely causes include monotonous visual stimuli (e.g., rapidly passing scenery outside), consistent white noise (such as the sound of wheels on tracks), comfortable seating, and stable cabin temperatures—all of which can induce “travel-related drowsiness.” Additionally, factors like circadian rhythms, sleep deprivation, or traveling after meals can further increase sleepiness.Admittedly, during extreme peak hours with severe overcrowding, localized CO₂ levels might temporarily rise if the ventilation system is overwhelmed—but such cases are rare, and operators typically adjust fresh-air intake to compensate. Thus, drowsiness on high-speed trains is better explained by a combination of physiological and environmental factors rather than CO₂ overexposure alone.
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