Although commonly called "diesels," the locomotives actually are electrically driven. The diesel engine drives an alternator, which produces electricity to run electric motors mounted on the locomotive's axles. The internal combustion engine was a dramatic improvement in efficiency over the steam locomotive, making substantial savings possible in maintenance and the elimination of widespread facilities. Extra units could be coupled together and run by one engineer from the lead unit, creating very powerful combinations.
No other railroad in this country has retained its historical equipment and honored its past like the Union Pacific. The preservation of its fleet speaks to the high value Union Pacific places on its heritage and its role in America's history.
Via the Union Pacific Railroad.