One short whistle means STOP. One long whistle (three to 10 seconds) means the train is approaching a station. Two short whistles mean that the engineer acknowledges that he or she heard or saw a signal that affects movement. Three short ones mean that the engineer intends to make a reverse movement.
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!
By 1938, the Association of American Railroads had adopted the long-long-short-long signal for rail crossings. But whatever the horn pattern, the goal is to warn people well in advance that a train is coming. In 2021, 236 people were killed at highway-rail grade crossings in the US.
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.
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.
You may have noticed that a train whistle gets lower as it passes you. The whistle is not changing pitch, but you are hearing a change. This principle is known as the Doppler effect. The Doppler effect is named after the Austrian physicist, Christian Johann Doppler, who discovered it.
- One long whistle-like sound can be heard when the train is coming to a halt, and the engineer applies the air brakes. - Two long honks mean that the train has released the brakes and is ready to continue its journey.
The intensity of sound will vary at night, sometimes louder and sometimes softer. 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.
Locomotive horns serve a utilitarian function and in North America with its wide open spaces, sparsely populated areas between cities and infrequent rail traffic (compared to Europe) a louder horn and more frequent blasting makes practical sense.