A railbus is a lightweight passenger railcar that shares many aspects of its construction with a bus, typically having a bus (original or modified) body and four wheels (2 axles) on a fixed base, instead of on bogies. Originally designed and developed during the 1930s, railbuses have evolved into larger dimensions, with characteristics similar in appearance to a light railcar, with the terms railcar and railbus often used interchangeably. Railbuses designed for use specifically on little-used railway lines were commonly employed in countries such as Germany, Italy, France, the United Kingdom and Sweden.
Today, railbuses are being replaced by modern light DMU railcar designs. Modern diesel-electric railcars, which can be run coupled as multiple units, like the Stadler RS1, the RegioSprinter of Siemens or the successor Siemens Desiro share role and specifications with railbuses (albeit with improvements in noise, low floor design, fuel efficiency, speed and other measures) but are usually not referred to by the term "railbus" any longer.
Locally manufactured TecnoTren railbuses are in use around Argentina, most notably on the University train of La Plata. They are mostly used in rural parts of the country where the tracks have not yet been repaired and so can't handle the weight of regular trains.
In 1937, the NSW Department of Railways added six Waddington-built four-wheel streamlined FP Paybuses to serve on small branch lines out Cowra and Harden that did not have enough passengers to justify a rail motor. Powered by a Ford V8 engine, they were given the designation FP1 to FP6. When the railbus service wasn't popular, several of the buses became mobile pay cars used to pay railway employees at stations and working on tracks.
In December 1941, one of these railbuses (FP 5) was destroyed when dynamite was placed on railway tracks near Yanderra. The three-man crew of the railbus were killed in the explosion. Though £2,000 of loose cash was taken, the safe in the railcar could not be opened by the robbers.