Windscreens on Tube trains have their impact resistance tested by firing a 1kg mass at them at 233km/h.
I've just been reading a fascinating article about the process of finding a new supplier of windscreens for Tube trains after the factory that has been making them for decades closed down in 2020. What I'm not sure of is the significance of that speed.
ETA: it's not just Tube trains but all trains. BS EN 15152 applies.
That's interesting - and I can't help but speculate wildly.
Perhaps this is derived from the maximum closing speed of two opposing tube trains. i.e. something comes off one, hitting the other whilst they are both closing at max speed.
Top speed of tubes today is 60mph - which is 193kph for 120mph closing speed: But if there is a 12.5% engineering uplift, just in case, then that gets 233kph.
Complete speculation on my part - but I think there is some logic in the biggest speeds being two closing trains?