My doodlebugs are the only locomotion that operates between multiple train sections.  It runs between the US Farming & Farming Town and the Eastern Avenue – Old US Costal City passing through the Light Industry & Land Works and the Heavy Industry & Switch Yard.

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, obviating the need to operate conventional trains consisting of a locomotive and coaches. Several railroads, mostly small regional and local networks, provided their main passenger services through doodlebugs in a cost cutting effort.

In the United States, doodlebug was the common name for a self-propelled railroad car (multiple unit). While such a coach typically had a gasoline-powered engine that turned a generator which provided electricity to traction motors, which turned the axles and wheels on the trucks, versions with mechanical transmissions also existed.