The history of steam road vehicles comprises the development of vehicles powered by a steam engine for use on land and independent of rails, whether for conventional road use, such as the steam car and steam waggon, or for agricultural or heavy haulage work, such as the traction engine.
The first experimental vehicles were built in the 17th and 18th century, but it was not until after Richard Trevithick had developed the use of high-pressure steam, around 1800, that mobile steam engines became a practical proposition. The first half of the 19th century saw great progress in steam vehicle design, and by the 1850s it was viable to produce them on a commercial basis. This progress was dampened by legislation which limited or prohibited the use of steam powered vehicles on roads. Nevertheless, the 1880s to the 1920s saw continuing improvements in vehicle technology and manufacturing techniques, and steam road vehicles were developed for many applications. In the 20th century, the rapid development of internal combustion engine technology led to the demise of the steam engine as a source of propulsion of vehicles on a commercial basis, with relatively few remaining in use beyond the Second World War. Many of these vehicles were acquired by enthusiasts for preservation, and numerous examples are still in existence. In the 1960s the air pollution problems in California gave rise to a brief period of interest in developing and studying steam powered vehicles as a possible means of reducing the pollution. Apart from interest by steam enthusiasts, the occasional replica vehicle, and experimental technology no steam vehicles are in production at present.
Early research on the steam engine before 1700 was closely linked to the quest for self-propelled vehicles and ships; the first practical applications from 1712 were stationary plant working at very low pressure which entailed engines of very large dimensions. The size reduction necessary for road transport meant an increase in steam pressure with all the attendant dangers, due to the inadequate boiler technology of the period. A strong opponent of high pressure steam was James Watt who, along with Matthew Boulton did all he could to dissuade William Murdoch from developing and patenting his steam carriage, built in model form in 1784.