Thanks, as a person working more or less tangentially in rail this was really interesting to just quickly page through. Also loved that the author's last name is "Oldknow", this seems like old wisdom for sure!
At the end there is some text "sinusoidal characteristic". This is a control system, and (unlike the system of a bicycle) with increased speeds it will go unstable, the oscillations will continue to increase uncontrolled. This is why faster trains are an engineering accomplishment worth displaying. They require flatter cones which then require straighter track built to higher specifications.
Doo doo, do doo de doo, do doo de doo.
Doo doo, do doo de doo, do doo de doo.
Doo doo, do doo de doo, do doo de doo.
Doo doo, do doo de doo, do doo de doo.
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