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A train whistle or air whistle (originally referred to as a train trumpet or air trumpet) is an audible signaling device on a Steam locomotive or gas locomotive, used to warn that the train is approaching, and to communicate with rail workers. Modern diesel and electric locomotives primarily use a powerful air horn instead of a whistle as an audible warning device. However, the word whistle continues to be used by railroaders in referring to such signaling practices as "whistling off" (sounding the horn when a train gets underway).
The need for a whistle on a locomotive exists because trains move on fixed rail tracks and thus are uniquely susceptible to collision. This susceptibility is exacerbated by a train's enormous weight and inertia, which make it difficult to quickly stop when encountering an obstacle. Hence a means of warning others of the approach of a train from a distance is necessary. As train whistles are inexpensive compared to other warning devices, the use of loud and distinct whistles became the preferred solution for railway operators.
were almost always actuated with a pull cord (or sometimes a lever) that permitted proportional (tracker action) 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, known as "quilling", and it was often apparent who was operating the locomotive by the sound. Modern locomotives often make use of a push button switch to operate the air horn, eliminating any possibility of altering the horn's volume or pitch.
Another very popular American train whistle was, again, a Nathan product. This was a five-note whistle, with a much shorter bell, and therefore, much higher in pitch. This whistle produced a bright G-major 6th chord (GBDEG) and, again, was heavily imitated, copies being made by many different railroads.
The most popular American chime train whistle was the three-note version. These were either commercially made (Crosby, Lunkenheimer, Star Brass, Hancock Inspirator Co. among others) or shop-made by the railroads themselves. Some famous and very melodious shop-made train whistles were Pennsy's passenger chimes and the Baltimore and Ohio's step-top three chimes, as well as the Reading Company six-chime whistle used on passenger locomotives. But the most beloved of all three-chime train whistles to the public and railroaders alike were the deep-chorded "steamboat minor" long-bells. A well known commercially made chime was Hancock Inspirator Company's three-note step top. These found use on almost every American railroad. Some railroads copied these also, examples being found on the old St. Louis–San Francisco Railway, Southern Railway (U.S.) and Illinois Central.
The need to blare a train's whistle loudly to be heard by the driver of a vehicle approaching a grade crossing has become a major disadvantage to the use of train whistles as a safety device and has caused much controversy among those living within earshot of the train's whistle. It has been documented that a train's whistle, when operating on compressed air, driving an exponential horn, has been measured at a higher decibel levels within the homes of nearby residents than within the cab of a vehicle sitting at the grade crossing.
Given the tonal design of the train whistle, the sound level, how often trains pass through a given community, the number of grade crossings in proximity, and the time of day (night) of occurrence, community residents residing near crossing sometimes feel that train whistles have a serious detrimental effect on the quality of life despite the gain in safety that sounding the horn provides to motorists and pedestrians. However, one Federal Railroad Administration study has shown that the frequency of grade crossing accidents increases in areas where quiet zones are in effect. The study fails to account for other factors that were also introduced at the same time which may have also accounted for the reduction in accidents during the same period the study measured. For instance, it was during the same period that locomotives began sporting the now crucially important tri-lamp headlight arrangement ("ditch lights") and reflector strips similar to those commonly found on highway tractor-trailers. Additionally, the measurements were based on accidents at grade-crossings, which are very low numbers overall to begin with. A grade-crossing that had two accidents during the comparison years, when contrasted with only one accident during the control period, would statistically yield a high percentage-wise improvement in safety, when in reality, it was the difference in only one accident for that grade-crossing.
Conversely, there are those who do not object to the train whistle, as they believe it provides an important safety feature.There were over 3000 wide ranging public comments regarding quiet zone rule. 70 FR 21844, [1] Some people even like the sound of the whistle, as it calls to mind a nostalgic era, as with the riverboats and their steam whistles and calliopes. However, no real studies have been performed by unbiased official entities to measure the real effects such noise has on a community.
Signals below are American practice: represents short sounds, and for longer ones.
| Acknowledgment of any signal not otherwise provided for | |
| When train is stopped: backing up, or acknowledgment of a hand signal to back up; when moving: stop at next station | |
| Request for a signal to be given, or repeated if not understood | |
| When train is stopped: air brakes are applied and pressure is equalized | |
| Train releases brakes and proceeds | |
| Flagman return from the west or south | |
| Flagman return from the east or north | |
| Inspect the brake system for leaks or sticking brakes | |
| Warning that a second section of a timetabled train is following | |
| Instruction for flagman to protect rear of train | |
| Train is approaching public grade crossing(s), known as Rule 14L in almost all railroad operating rules; also used in Australia | |
| Series of short blasts | An emergency exists, or if persons or livestock are on the track |
| Stand by or general acknowledgement | |
| Apply or increase manual brakes | |
| Apply manual brakes to stop the train as soon as possible | |
| Approaching railroad station or blind curve | |
| Decrease manual brakes; when repeated, fully release brakes | |
| Prepared for change of tracks, crossing or other situations that requires a gentle approach | |
| Multiple short | Danger |
These are some of the signals used in Finland:
| Engine is starting forwards | |
| Engine is about to move backwards | |
| Warning, used approaching a crossing | |
| Danger |
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