Originally Posted by Chris Lord:
Pardon my ignorance but why would you want to intentionally derail a car in this way? Seems to be an accident waiting to happen.
As stated above, you would want to derail a car for a number of reasons. To prevent a car from rolling onto a high-traffic main line; to prevent a car from rolling into the drink at a drawbridge, etc. On a siding for a petroleum plant, you might not want a cut of tank cars loaded with gasoline rolling into the path of an on-coming passenger train, so you derail the cars before they get that far.
