When American freight trains delivered cargo after World War II, the steam-belching beasts commonly had seven people aboard — an engineer, a conductor, up to four brakemen and a fireman.

Trains have since grown much longer, seemingly stretching to the horizon and often taking 20 minutes to pass through a crossing. And crews have been reduced in size — to five people in the 1970s and two in 1991. Now U.S. railroads want to put a single person in charge of today's huge locomotives, taking another step toward a future in which the nation's rail-cargo system increasingly could resemble toy train sets — highly mechanized networks run by computers or distant controllers.

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