1.White noise

白噪音

Cars and other vehicles are a perfect environment that produces white noise. It's a consistent noise, like the hum of tires or the purring of the car. White noise masks distracting sounds, and is helpful for people who have trouble getting sleep.

汽车和其他车辆是产生白噪声的完美环境。它是一种始终如一的噪声，如轮胎的嗡嗡声或汽车的呜呜声。白噪音掩盖了分散注意力的声音，对睡眠困难的人很有帮助。

When you're riding a vehicle, white noise is continuously emitted, making it easier for passengers to drift off to dreamland.

当乘客坐在车上时，白噪音会不断地释放出来，使人们更容易进入梦乡。

2.Rocking motion

摇晃

Another popular view as to why it's easy to fall asleep in buses or trains is because of the rocking motion that's similar to what lulled us to sleep when we were babies.

另一种流行的观点认为，在公共汽车或火车上很容易入睡是因为摇摆，这种摇摆类似于我们还是婴儿时被哄睡的动作。

However, it's not the rocking movement, per se, that induces sleep. Rather, it's the association between rocking and sleeping. If you were rocked to sleep as a baby, you'd have that association that when you experience a rocking motion, you go to sleep.

然而，并不是摇摆动作让人入睡，而是摇摆和睡眠之间的联系。如果你在婴儿时被摇晃着入睡，你就会把摇晃的动作和入睡联系起来。

3. Increase in carbon dioxide in public transportation

公共交通工具内的二氧化碳增加

Buses and trains get crowded everyday with people going to and from work. Carbon dioxide increases when there are lots of people in a small space. This reduces oxygen to the brain and slows it down.

公共汽车和火车每天都挤满了上下班的人。当一个狭小的空间里有很多人时，二氧化碳浓度就会增加。这会减少大脑中的氧气并让大脑变得迟缓。