A EMD SD40-2 from the movie Unstoppable. When a massive, unmanned locomotive roars out of control, the threat is more ominous than just a derailment. The train is laden with toxic chemicals, and an accident would decimate human life and cause an environmental disaster. The only hope of bringing the train to a safe stop is in the hands of a veteran engineer and a young conductor , who must risk their lives to save those in the runaway's path