The locomotive leads the train and pulls all other cars. Equipped with the cab, engine, headlights and horns, the locomotive starts and stops the train.
In the past, steam engines required frequent stops to reload coal and water for crewmembers to keep the fire burning. In the 1930s, the more efficient diesel-electric engines began replacing the older steam models.
Union Pacific's roundhouse, Salina, KS, July, 5, 1923.