cngw,
There are many, many. locations on US railroads withe the same type of derail system. Lots of locations with single "movable point derails" and for absolute positive protection,i.e approaches to lift/draw/swing bridges, high traffic main line crossings at grade, and heavily used sidings, the "double movable point derail". When you want to be sure that the train is COMPLETELY derailed, the the twin "movable point derail" type is used.
As you can see in the video above, the twin point system works every time!
Concerning your other questions, please refer to Big Jim's post, directly above yours. He gives the answer as to WHY it happened.
