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A semi-related surprising fact I only learned recently is that the ultra-long nose of Japanese bullet trains is not for aerodynamics, but to reduce noise. Specifically, "tunnel boom."

Random source: https://www.jrpass.com/blog/why-shinkansen-bullet-trains-no-...

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this is only a problem in japan because the shinkansen is the oldest high speed network in existence.

new train tunnels built in Europe are wider and flare out at the end so that there isn't a tunnel boom.

Fascinating, and now I learned another new thing! Thank you for sharing.

yup. for a more detailed explanation, there's this segment of the article:

> Basically what happens is when a train enters a tunnel at high speed, the air in front of it is compressed and does not have enough time to flow past the trains body. When all released at once, the pressure causes a shockwave that goes boom!

This is basically a very rudimentary version of the piston effect: https://en.wikipedia.org/wiki/Piston_effect

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