And a runaway train cant be stopped with a derailer

@1M Cool Things:

Derails are commonly used to protect certain parts of track. For example, if a work crew is working on a siding, they will put derails on both ends of the siding. So if a car rolls onto the siding, the derail will derail the car rather that roll of equipment or workers. Place your derail on the side of the rail as shown in the picture.

-Pyro Tank

how do i use it?