Train noise

Key takeaways

Train noise belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Train noise to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Train noise from memory before moving on to harder problems.

Reference excerpt

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.

Roughness and irregularities on the wheel and rail surfaces are a source of noise and vibration. Rail joints and squats on the rail cause a familiar "clickety-clack" sound as train wheels roll over them. Rail corrugation (a periodic wear pattern resembling corrugated metal) causes tonal noise and vibration; fine, short-wavelength corrugation is known as "roaring rails" due to its high-pitched sound, whereas coarse, long-wavelength corrugation can cause the ground and nearby buildings to vibrate. Rail roughness and corrugation are treated by grinding the rails. This reduces noise in problem areas although trains make a distinctive tonal sound on freshly-ground track due to the pattern on the rail left by the grinding process, which wears flat over time. Rail squeal is a sound caused by a train's wheels slipping under specific conditions, usually around sharp curves. Air displacement of a train in a tunnel can create noise from turbulence. Trains also use horns, whistles, bells, and other noise-making devices for both communications and warnings. The engines in diesel locomotives and DMUs produce significant amounts of noise. Newer locomotives have become much quieter in recent years due to noise regulations being implemented by countries and regions. However, there are still times that a locomotive may develop a defect in its turbocharger, which produces a whine that can be heard for many kilometres. While this is rare, and usually the said locomotive gets put into the shop quickly, the noise has been compared to an air raid siren, or a very large leaf blower. It appears to be the most common on units built by EMD (Caterpillar's locomotive division) equipped with the 710 series prime mover, although any turbocharged locomotive may develop this problem. Electric traction motors often produce electromagnetically induced noise. This high-pitch noise depends on the speed and torque level of the machine, as well as the motor type. Variable-frequency drives use pulse-width modulation, which introduces additional current harmonics and results in higher acoustic noise. The switching frequency of the PWM can be asynchronous (independent of speed) or synchronous (proportional to speed), but always results in acoustic noise varying with speed.

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:

See also Active noise control Adhesion railway Brake squeal Noise health effects Roadway noise Environmental noise

References

Bibliography Thompson, D.J. (2008). Railway Noise and Vibration. Elsevier Science. ISBN 9780080451473.

Illustrations

Worked examples

Example 1 — a first encounter with Train noise

Start with the simplest possible case. Write down what Train noise claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Train noise before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Train noise ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Train noise

In research: Train noise appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Train noise in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Train noise is common in secondary-school and first-year university syllabi. It links to neighbouring topics Mechanical vibrations, Noise pollution, Rail transport stubs, so understanding it makes those chapters shorter.
In everyday life: Look for Train noise outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Train noise in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Train noise means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Train noise out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Train noise in simple terms?

Train noise is vehicle noise made by trains. Noises may be heard inside the train and outside.

Why does Train noise matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Train noise?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Train noise.