At night, the air near the ground can have a different temperature than air only a few hundred feet above1. This affects the transmission of sound waves. There is usually less ambient noise after dark, so the distant train sounds louder.
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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.
Sound travels fastest through solids and slowest through air. So the sound waves sent by the train on the track reaches the human ear faster through the train track than the air. The sound reaches us more slowly through air.
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 ...
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.
Anyway, don't blame the engineer: They're required to blow that horn. The regulation in question is called the Final Rule on the Use of Locomotive Horns—a name that strongly implies they've had just about enough of your bitching—and it requires four blasts 15 to 20 seconds before every crossing.
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.
Cold air decreases the velocity of sound, but doesn't affect it's intensity. However, the snow covered, windless environment would likely reduce the ambient noise environment, making it possible for more distant sounds to be heard than usual. Also, your valley location might magnify distance sounds in unexpected ways.
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.
In a quiet zone, railroads have been directed to cease the routine sounding of their horns when approaching public highway-rail grade crossings. Train horns may still be used in emergency situations or to comply with other Federal regulations or railroad operating rules.
Guests are asked to limit conversation and speak in subdued tones. Phone calls are not allowed and all portable electronic devices must be muted or used with headphones (passengers using headphones must keep the volume low enough so that the audio cannot be heard by other passengers).
The length, height, width, and composition of the building and its distance from the tracks, determines its natural oscillating frequency and the train's length and speed must create an oscillation that closely matches the building's frequency (or its harmonics), so that the small train vibrations get amplified to ...
Main passenger lines often have night trains and freight traffic to avoid disturbing day time passenger traffic, on top of that, many locomotives will tow broken trains, newly delivered trains, trains that need to move between depot, and retired trains that are transported to a destruction yard or to other companies.
Train horns may be sounded in emergency situaons or to comply with other railroad or FRA rules even within a quiet zone. Quiet zone regulaons also do not eliminate the use of locomove bells at crossings.
Answer #1: It's a wave of communicating between the train driver and workers on the tracks to acknowledge that the driver has seen them. Answer #2: For safety reasons – to make sure the horn is working before you leave the station.
If for no other reason, the horn can alert those folks to get to safety. either to alert people when they enter the tunnel(like MOW, or trespassers) or in some cases, to be friendly at kids(or railfans) at the tunnel entrance.