Railmotor is a term used in the United Kingdom and elsewhere for a railway lightweight railcar, usually consisting of a railway carriage with a steam traction unit, or a diesel or petrol engine, integrated into it.
Steam railcars
Overview
In the earliest days of railways, designers wished to produce a vehicle for passenger carrying that was economical to build and operate on routes where passenger numbers were light. A single coach with its own prime mover was a solution adopted in some cases; this may be thought of as the predecessor to the railcar, a term more associated with the use of internal combustion engines.
William Bridges Adams started building railmotors in small numbers as early as 1848. The Bristol and Exeter Railway used a steam carriage.
In most cases the early designs were unsuccessful technically, but in the early years of the twentieth century, street-running passenger tramways started to use small steam engines to draw tramcars, replacing the customary horse traction. In many cases the tramways soon adopted electric traction instead, and the attractiveness of the cheap and frequent conveyance abstracted business from the railways in urban areas.
The railways responded by opening new stopping places (to serve more closely the new suburban housing) and sought to reduce their operating cost by reintroducing railmotors, which were cheaper to construct.
The London and North Western Railway, Lancashire and Yorkshire Railway, London, Brighton and South Coast Railway, Great North of Scotland Railway and Great Western Railway introduced them.
Nonetheless, the railmotors had a number of disadvantages: their frequency, and the closeness of their stopping places, could not match that of the tramcars. The intrinsic compromises in fitting a steam engine inside the limited space available made them mechanically inefficient, and their power was (in most designs) insufficient to handle attached vehicles for parcels or additional coaches at times of exceptional demand such as public holidays; and in nearly all cases they still required a three-man crew (driver, fireman and guard), a significant expense compared with the single crew member of a tramcar.
They also encountered operational and maintenance problems on railways used to treating locomotives and carriages as separate entities: Servicing the prime mover in a locomotive shed or workshop frequently made the carriage body and interior dirty, and some railmotor designs required that some mechanical work be carried out from inside the carriage portion which aggravated the problem. Stabling railmotors in carriage sheds meant introducing the unit's smoke, steam, ash and dust into a relatively clean environment and requiring more effort to keep not only the railmotor but other carriages stabled alongside it suitably clean, and carriage sheds did not have staff trained in servicing and maintaining the power units of railmotors. Some railways invested in dedicated sheds to store and service railmotors, but this merely introduced additional running and manning costs which further reduced the railmotors' supposed economy of operation.
Designs
There were two basic designs: A small 0-4-0 or 0-2-2 steam locomotive with one end of a coach hung on it like an articulated lorry. A coach with a steam engine built into one end of it. This type would sometimes have a vertical boiler.