The subway noise levels are around 90db. As you can tell from this brief scale, noises can reach unsafe levels rapidly. Most people do not have prolonged exposure to the sound of a subway train, but many face occupational noises that are equally as loud all day long.
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.
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 ...
- 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 horn alerts people that a train is approaching a railroad crossing. It can also be used to warn animals or trespassers in our right-of-way along a section of track. Many people don't realize that federal and state regulations require us to sound the horn whenever we approach any crossing.
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.