Basically this dude smuggles a russian nuclear warhead (jeeze, thats original) onboard a train headed by a couple of D9's. Well, about 20 mins into the movie, the air hose breaks, and guess what? the train just continues to gain speed travelling out of control down a mountain and into denver
now, call me stupid, but when a brake hose breaks, then dont the breaks come ON?
well anyway, the nuke goes off, poisoning thousands of people and destroying the city of denver.