Trainclown, it look's like everyone beat me to the punch, it is a derail all right, most derails are in the yards to protect shop tracks or tracks where people are working. That's there main purpose, to derail a locomotive before it runs you over. All Mechanical tracks in most yards that have service tracks, use derails as a safety precaution, once staff are going to work on a track, derails are put in place. Every derail will be marked on a pole with a "D" as in the picture. The one in the picture is a double derail, this will derail from both directions. This type of derail is when you have rolling stock movement on either sides therfore each side protects the other. If you look at the switch lock theres only one, that further tells that only one direction is being protected, if there were 2 locks then both sides would be protected. Each employee must apply a lock to the derail for protection. And only the employee that applied the lock can remove it. In the event that a lock is left on the supervisor then must ensure the track is clear prior to removing the lock.