I was thinking how little security is on display in British railway stations. Doors are left open and all sorts of people mill about the platforms.
What if some crazy were to hijack a train and crash it into the buffers in a main station? 40 tonnes at 120 MPH would be a disaster, if it couldn’t be diverted into a siding in time.
Today’s invention is a massive railway car which, in such an emergency, could be dropped onto the tracks using a purpose-built mobile crane outside a mainline station.
As a runaway train approached, the car would motor towards it and make gentle contact at matching speed. It would fire up a rocket motor, to retard the train and then apply its brakes so as to prohibit entry to any station.
A combination of these forces, under software control, would halt the train, without causing impact injuries to its occupants.