Why do I hear train noises at night?

There are two things that can be considered: one is trivial - that it is quieter at night so you are more likely to hear the horn. The second is physics: the speed of sound depends on the square root of temperature, so the refractive index is proportional to T-1/2.



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The reason that trains honk their horns so much at night is because it's dark and the trains aren't so easy to see. Even though the lights are on, we sometimes can't see them coming, especially around the many blind curves near or ahead of the train station.

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It has to do with the height and strength of a temperature inversion just above the ground. On clear, calm nights, it is cooler at the ground than higher up. When air warms with altitude a temperature inversion exists. Sound travels faster in warm air than it does in cool air.

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Have you ever thought why trains blow their horns so often and so loudly? The truth is that they have to. And the main reason for that is safety. Locomotive engineers are required to honk every now and then, which is written down in the regulations called the Final Rule on the Use of Locomotive Horns.

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Today, the only whistle signals you're likely to hear regularly are the grade-crossing warning (which is also often used to warn employees or others on the tracks); two (or three) shorts to indicate the engineer has received a signal to start the train forward (or backward); and one long blast when a train is ...

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“People assume that trains are loud, but that assumption is based on the fact that when a train's gone past them in a station it's noisy. That's because the noise a train makes is mainly projected to either side. When trains are moving directly towards you they are barely audible–until it's too late.”

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So, as you can see from the name, all this honking business is pretty strict and obliges trains to make four blasts approximately 20 seconds before they reach a crossing. But that's not all! Trains whistles and horns are an effective method of communication!

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With a quiet background (countryside night time) 6–8 miles. Suburban, 2–3 miles. Loud city, 1 mile if you're listening for it.

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Why do trains honk so loud at night? Train horns sound at the same volume whenever they are sounded. They often have minimum volume requirements, to ensure they can be heard far enough away for workers in a working environment to seek safety.

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Trains await daybreak inside the station or terminal, in the depots, where automatic alarms may start warming up the machine before departure (mainly for metros), in sidings next to the depots, or in tunnels in winter, for protection against cold and frost.

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Noise pollution and vibrations are some of the biggest concerns, particularly for people who live within one-third of a mile of railroads or railyards, says Natalia Caldeira Loss Vincens, an expert in public health at the University of Gothenburg in Sweden.

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“People assume that trains are loud, but that assumption is based on the fact that when a train's gone past them in a station it's noisy. That's because the noise a train makes is mainly projected to either side. When trains are moving directly towards you they are barely audible–until it's too late.”

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