The easiest ways to derail a train are damage the tracks, damage a bridge (possibly as the train goes over it), or leave something (eg a stolen car) in the trai

The easiest ways to derail a train are damage the tracks, damage a bridge (possibly as the train goes over it), or leave something (eg a stolen car) in the train's way. Not coincidentally, these are historically the most commonly used methods. Boarding a passenger car from which it is hard to get to the engine where the engineer is driving the train is far less likely to be effective.