Sound travels faster in warm air than it does in cool air. This means the sound of a train horn will bend downward when it passes through an inversion causing sound waves to propagate farther than normal.
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It is suggested in general that vibrations are not noticeable at distances over 300 m from the railway [23].
“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.”
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.
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.
By the time a train operator sees you, it is too late to stop the train in time. An oncoming train is moving faster and is closer to you than it appears. Similar to an airplane traveling at 150 mph that appears to float onto the runway, it's hard to determine a train's speed and distance from you.
Every three hours, a person or vehicle is hit by a train in the United States. However, many of these are preventable. This is one of the many reasons why being educated about rail safety is so important.
Under the Train Horn Rule (49 CFR Part 222, issued on August 17, 2006), locomotive engineers must begin to sound train horns at least 15 seconds, and no more than 20 seconds, in advance of all public grade crossings.
The intensity of sound (such as a train horn) that you hear will vary at night, sometimes louder and sometimes softer. The explanation is the height of the inversion above the ground.
Surrounding terrain also can affect sound. For instance, in the instance of a train passes through a corridor of trees, those trees can muffle the sound in much the same way as sound baffles that line the walls of a recording studio.