A steam car is a car (automobile) propelled by a steam engine. A steam engine is an external combustion engine (ECE) in which the fuel is combusted outside of the engine, unlike an internal combustion engine (ICE) in which fuel is combusted inside the engine. ECEs have a lower thermal efficiency, but carbon monoxide production is more readily regulated. Steam-powered automobiles were popular with early buyers. Steam was safe, reliable, and familiar. People had decades of experience with it in trains and boats, and even in experimental road vehicles. However, early steam cars required constant care and attention—and up to 30 minutes to start. Automated quick-firing boilers solved these problems, but not before more efficient gasoline engines dominated the market and made steam cars obsolete. The first experimental steam-powered cars were built in the 18th and 19th centuries, 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. By the 1850s it was viable to produce them commercially: steam road vehicles were used for many applications. Development was hampered by adverse legislation from the 1860s as well as the rapid development of internal combustion engine technology in the 1900s, leading to the commercial demise of steam-powered vehicles. Relatively few remained in use after the Second World War. Many of these vehicles were acquired by enthusiasts for preservation. The search for renewable energy sources has led to an occasional resurgence of interest in using steam technology to power road vehicles. Technology A steam engine is an external combustion engine (ECE: the fuel is combusted away from the engine), as opposed to an internal combustion engine (ICE: the fuel is combusted within the engine). While gasoline-powered ICE cars have an operational thermal efficiency of 15% to 30%, early automotive steam units were capable of only about half this efficiency. A significant benefit of the ECE is that the fuel burner can be configured for very low emissions of carbon monoxide, nitrogen oxides and unburned carbon in the exhaust, thus avoiding pollution. The greatest technical challenges to the steam car have focused on its boiler. This represents much of the total mass of the vehicle, making the car heavy (an internal combustion-engined car requires no boiler), and requires careful attention from the driver, although even the cars of 1900 had considerable automation to manage this. The single largest