Road steamers were vehicles powered by a steam engine and designed to be independent of rails. The main technical challenge to make these vehicles useful was to prevent their weight from causing deep grooves or ruts in their tracks.
In 1867, Robert William Thomson patented solid India-rubber tires for the road steamers manufactured in his Leith workshop. Fitted with this equipment, a vehicle like the one shown above could be driven across a meadow without the wheels sinking too deeply into the ground. On a flat road, it could tow 30 tons at a speed of 2.5 to 6 mph (4 to 10 km/h); it could reach 16 to 18 horsepower.
In England, some of these steamers were used to carry coal from mines to nearby factories. They were also used on an omnibus line in Edinburgh, and various tests were conducted by the postal administration in the province of Punjab in India.
The caption reads in the original French:
Locomotive routière, système Thomson.