They don't prefer trains that derail, but (if the article is to be believed, which I can't say) they prefer to chip away at the safety margins (which cost money

They don't prefer trains that derail, but (if the article is to be believed, which I can't say) they prefer to chip away at the safety margins (which cost money) until it's only the experience of the (train) engineer that keeps the train on the tracks. Of course, you could say that's always the case, but I can imagine that it gets harder and harder to do it the longer the train is.