Train whistle

A train whistle or air whistle (originally referred to as a steam trumpet) is an audible signaling device on a steam locomotive used to warn that the train is approaching, and to communicate with rail workers.

The older steam whistles were almost always actuated with a pull cord (or sometimes a lever) that permitted proportional (tracker) action, so that some form of "expression" could be put into the sound. Many locomotive operators would have their own style of blowing the whistle, and it was often apparent who was operating the locomotive by the sound. Modern locomotives often make use of a pushbutton switch, which takes away the fine control over the way the whistle is sounded.

Because trains generally have extremely high mass and relatively low braking friction, they are inherently difficult to stop at normal speeds. Some way of warning others of the approach of a train from a distance is necessary. Since train whistles were extremely inexpensive to institute compared to other more effective warning devices, the use of loud and distinct train whistles became the preferred solution for railway operators.