Doodlebug or hoodlebug is a nickname in the United States for a type of self-propelled railcar most commonly configured to carry both passengers and freight, often dedicated baggage, mail or express, as in a combine.[1] The name is said to have derived from the insect-like appearance of the units, as well as the slow speeds at which they would doddle or "doodle" down the tracks.[2] Early models were usually powered by a gasoline engine, with either a mechanical drive train or a generator providing electricity to traction motors ("gas-electrics"). In later years, it was common for doodlebugs to be repowered with a diesel engine.Doodlebugs sometimes pulled an unpowered trailer car, but were more often used singly. They were popular with some railroads during the first part of the 20th century to provide passenger and mail service on lightly used branch lines at less expense than with a train consisting of a locomotive and coaches with larger crew. Several railroads, mostly small regional and local networks, provided their main passenger services through doodlebugs in a cost-cutting effort.