Thanks for the explanation, John. I hadn't considered it being used as a protection for work crews.

Still seems like an extreme solution, though. Most likely, the first thing to hit the derailer is the locomotive pulling the train. Even if it stays erect after derailing, rerailing a locomotive seems like a non-trivial process, probably requiring a crane. If it's on its side, how many cars has it pulled over with it, and what do those cars contain? (rhetorical question)