I have recently travelled by train over parts of Europe, and have been amazed at the smooth, stable ride at speeds of up to 300 km per hour. The track is rail on ballast, as it has been for 180 years.
How do the European railways keep the track so stable? I have looked at some rail forums but the contributors don’t seem to have any technical knowledge. I have seen Youtube videos of ingenious rail maintenance equipment, but I am not much the wiser. One of the high speed trains I travelled on, between Lille and Charles de Gaulle airport, was double decker, at 300 km per hour! Any side to side rocking will be amplified by two decks.
There have been proposals for over a hundred years to have rail carriages stabilised by gyroscopes, spinning round a vertical axis. The original plans were to replace two rails with one, and have an active gyroscope using precessional forces to stabilise the carriages. I can see that a gyroscope stabilising a conventional two rail train could be passive, and rely on the inertia of the spinning gyros to dampen side to side movement. I have not heard that gyros are used to stabilise trains.
Any ideas?