Train noise is vehicle noise made by trains. Noises may be heard inside the train and outside. Subway systems, light rail transit and freight trains can send loud train noise into neighborhoods. Organizations such as the World Health Organization and the U.S. Environmental Protection Agency have set guidelines for noise level decibel limits for rapid transit. Noise levels can be reduced by installing noise barriers next to the track. Traditional clickety-clack sounds occur as a result of gaps in the rail to allow for thermal expansion. On most railways, the gaps are opposite each other and if the carriages are about the same length as the rails, an even clickety clack sound is generated. In the USA the rail joints are staggered, so not being opposite each other, a different and irregular sound is heard.

Sources

Several distinct sounds are created by various parts of the train, such as engines, traction motors, brakes, and the wheels rolling on the rails.

Rail squeal

Rail squeal is a screeching train-track friction sound, commonly occurring on sharp curves. Squeal is caused by the flanges of the wheels scraping across the railhead. The "Howling sound" is caused by lateral sticking and slipping of the wheels across top of the railroad track. This results in vibrations in the wheel that increase until a stable amplitude is reached. Lubricating the rails has limited success. Speed reduction also appears to reduce noise levels. The sticking of the rim of the wheel causes the wheel to ring like a bell, so rubber dampers or tuned absorbers are a possible solution to lower the volume. The MBTA Green Line, for example, suffers from severe rail squeal on the sharp curves within the central subway. Flange stick graphite lubricators have been installed on trains to attempt to mitigate the rail squeal issue. The mechanism that causes the squealing also is the cause of wear and tear that happens in the wheel–rail interface. Factors affecting rail squeal include: