Among the other good answers here, some metro designs (e.g. Montreal) use rubber tires instead of typical train wheels, and also wood brake pads saturated with some kind of oil (although I wouldn’t be surprised if the brake materials were changed with the cars that were put in use in that couple of years.
UPDATE: the brakes are soaked in peanut oil. https://youtu.be/MdvQLYC5hGc
Not sure how many systems use this design around the world though.
They are lighter per car, and shorter. Additionally, they are designed to be relatively quiet, and the routes are designed to project less sound. Much of that is because metros are usually electrically driven, which replaces the big Diesel engine. Trains are meant just to be powerful; sound is an afterthought.
For reference, each train car can vary between 30 to 130 tons depending on what’s in it, and there could be several dozen cars to a train. Subway train cars aren’t light at 38 tons, but they’re on the light end of the range, and their aren’t many of them.
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