[tialaramex]

Even at 75mph this stuff is all unsafe and wouldn't be legal if it wasn't essentially a museum on wheels.

A modern multiple-unit is way stronger and built from things which are designed to bend and then once they exceed maximum load, tear into non-sharp pieces, which means when (not if) something goes badly wrong it's much more survivable for the occupants. At 5mph you aren't too bothered, but older coaches would deconstruct into sharp pieces in even a 50mph collision so the accident ends up more lethal than it would be if you weren't inside a vehicle at all.

Years back a cement mixer truck fell off a bridge onto a moving train. It was a modern design, and so even though obviously such a truck is incredibly heavy it just dented the train and the person directly below the impact inside the train survived (with some injuries). With the older carriages used on a heritage railway it would have demolished the entire carriage and turned everybody inside it into paste, the emergency response would have been recovering remains, not rescuing one guy with head injuries and a bunch of scared but otherwise unharmed passengers.