TRAIN

A person on railroad tracks hear a train approaching, looks behind him, sees the train and then freezes on the tracks in fear. The train "outruns" its sound--which means that by the time you hear it, it is virtually on top on you. If a train engineer sees you on a track, he or she will blow the whistle. Often it takes more than one blast to get the average person's attention, say train engineers. But trains can't stop the way motor vehicles can. A freight train has about 100 cars, weights 12 million pounds, and takes a full mile to stop. An optical illusion happens with tracks. When you see a train coming, it looks as if it is traveling half as fast, and is two times farther away from you than it really is. For example, if it is going 60 miles per hour and is half a mile away, it looks as if it is traveling 30 mph and is one mile away. 

Dennis Heatherington, Operation Lifesaver, in MSC Health Action News, Vol XIV, No. 3, March 1994, p. 4.