Sure, it's unguarded, but how much damage can a motivated attacker actually do by sabotaging a rail line? The worst I can think of is spilling a few carloads o

Sure, it's unguarded, but how much damage can a motivated attacker actually do by sabotaging a rail line? The worst I can think of is spilling a few carloads of radioactive waste. That requires knowing when the train will be coming, as well as whether there's any trains in front of it. (Obviously, you don't want your efforts going to naught due to an unexpected lumber train.) Since freight trains don't particularly travel on any schedule, you'll have to have a man watching the tracks all the time, and be prepared to break the rail or commit other mischief on short notice. If you choose to break the rail outright, you'll want to note that most track in the United States is protected by track circuits, which detect when the rail loses electrical continuity, and lights the "track occupied" light ( http://en.wikipedia.org/wiki/Track_circuit#Circuit_failures http://en.wikipedia.org/wiki/Track_circuit#Circuit_failures ). Even after you go to all this trouble, it's most likely that the only failure you'll cause by derailing the front of a train is a delay to other trains. Garden variety milk-tank cars are designed to survive a derailment, because derailments happen and the product is worth money. Cars that carry radioactive waste are almost certainly better reinforced. You can have a man sitting next to the track with dynamite on a radio detonator. He's going to have to have a good deal of it, and time it right to be under the cars that matter. This requires, again, knowing when the train is coming, and visiting the track on short notice. You'd not want to leave the explosives in place permanently, because the tracks do get inspected regularly. And then you'll have to deal with the reinforced railcars anyway. I'm going to cut this off here, since I'm 8 hours late to the discussion.