> I always wondered why no-one tried (or maybe they have?) to develop some
> kind of breaking system for RR cars that didn't depend on the wheels (for
> example, solid-fuel rocket motor) that could be used in an extreme
> emergency to stop the train QUICKLY. I realize that this is changing the
> subject slightly from the safety concern you mentioned, but it made me
> think of it.

It's a problem of getting rid of the energy. You could maybe do something
that drops down and digs up the trackbed, but rockets would be a BAD idea.
Barbecueing railroad workers at random would probably upset the union, and
after a derailment, it would be an interesting task to get in there with
rocket motors live in the mix.

I wouldn't mind getting some spares after the project was scrapped though,
that would be at least an S class motor, probably more like V.. :)