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Steam powered road roller
steam powered road rollers

A steamroller (or steam roller) is a form of road roller – a type of heavy construction machinery used for leveling surfaces, such as roads or airfields – that is powered by a steam engine. The leveling/flattening action is achieved through a combination of the size and weight of the vehicle and the rolls: the smooth wheels and the large cylinder or drum fitted in place of treaded road wheels. The majority of steam rollers are outwardly similar to traction engines as many traction engine manufacturers later produced rollers based on their existing designs, and the patents owned by certain roller manufacturers tended to influence the general arrangements used by others. The key difference between the two vehicles is that on a roller the main roll replaces the front wheels and axle that would be fitted to a traction engine, and the driving wheels are smooth tired. The word steamroller frequently refers to road rollers in general, regardless of the method of propulsion.

Before about 1850, the word steamroller meant a fixed machine for rolling and curving steel plates for boilers and ships. From then on, it also meant a mobile device for flattening ground. An early steamroller was patented by Louis Lemoine in France in 1859 and demonstrated sometime before February 1861. In Britain, a 30 ton steamroller was designed in 1863 by William Clark and partner W. F. Batho. The company Aveling and Porter was the first to successfully sell the product commercially and subsequently became the largest manufacturer in Britain. The heavier rollers were found to be hard to handle and the weight of the machines was reduced to around 10 tons. Production ended around 1950.

[[File:Robey Tandem Great Dorset Steam Fair. jpg|thumb|right|1925 Robey tandem roller #42693, now owned by the Robey Trust Ten tandem and two tri tandem Robey rollers survive in preservation, and one of the tri tandems is known to have been used to construct parts of the M1 motorway. A variation of the basic configuration was the "convertible": an engine which could be either a steam roller or a traction engine and could be changed from one form to the other in a relatively short time – i. e., less than half a day. Convertible engines were liked by local authorities, since the same machine could be used for haulage in the winter and road mending in the summer.

Although most steam roller designs are derived from traction engines, and were manufactured by the same companies, there are a number of features that set them apart.

The most obvious difference is in the wheels. Traction engines were generally built with large fabricated spoked steel wheels with wide rims. Those intended for road use would have continuous solid rubber tyres bolted around the rims, to improve traction on tarmac. Engines intended for agricultural use would have a series of strakes bolted diagonally across the rims, like the tread on a modern pneumatic tractor tyre, and the wheels were typically wider to spread the load more evenly. Steam rollers, on the other hand, had smooth rear wheels and a roller at the front. The roller consisted of a pair of adjacent wide cylinders supported at both ends. This replaced the separate wheels and axle of a traction engine.

In the conventional arrangement, the front roller is mounted centrally, forward of the chimney. In order to allow enough clearance from the boiler (and hence a larger front roll), the smokebox is extended forward substantially at the top to incorporate a support plate on which to mount the bearing for the roller assembly. This gives the distinctive, hooded look to the front of a steam roller. It also necessitates a different design of smokebox door – it has to hinge up or down, rather than opening sideways, due to the limited access available. Access to the boiler tubes for cleaning is limited and the brush usually has to be inserted through the small gap between the top of the roll and the fork.

The front and rear rolls were usually fitted with scraper bars. As the vehicle moved along, these removed any surface material that had become stuck to the roll, to prevent a build up of material and ensure a flat finish was maintained. Some steam rollers were fitted with a scarifier mounted on the tender box at the rear. They could be swung down to road level and used to rip up the old surface before a road was remade. Another accessory was a tar sprayer – a bar mounted on the back of the roller. This was not a common fixture.

Britain was a major exporter of steam rollers over the years, with the firm of Aveling and Porter probably being the most famous and the most prolific. Many other traction engine manufacturers built steam rollers, but after Aveling and Porter, the most popular were Marshall, Sons & Co., John Fowler & Co., and Wallis & Steevens. In America, the Buffalo Springfield Roller Company was a large builder. J. I. Case made a roller variant of their farm engines, but had a small market share. Other nations had makers including the Czechs, Swiss, Swedes, Germans (notably Kemna) and Dutch which produced steam rollers.

Two popular American bands were named for steamrollers, Buffalo Springfield and Mannheim Steamroller. British steeplejack and engineering enthusiast Fred Dibnah was known as a national institution in Great Britain for the conservation of steam rollers and traction engines. The first engine he restored to working order was an Aveling & Porter steam roller, registration no. DM3079. Built in 1912, it was a 10 ton slide valve, single cylinder, 4 shaft, road roller. Originally named "Allison", after his first wife, Fred renamed the engine "Betsy" (his mother's name) following his divorce – Fred's view being "wives may change but your mother remains your mother!" This roller was featured in many of Fred's early television programmes. It may still be seen at steam rallies in Britain and was in steam at the Great Dorset Steam Fair in 2011. In the Japanese manga and anime series JoJo's Bizarre Adventure, Dio the vampire infamously attempted to crush Jotaro by dropping a steamroller on top of him. Author Terry Pratchett instructed his collaborator Neil Gaiman that anything Pratchett had been working on at the time of his death should be destroyed by a steamroller. Pratchett's daughter and literary executor Rhianna Pratchett also stated that she had no desire to try to finish her father's work or continue the Discworld franchise without him. Accordingly, Pratchett's assistant Rob Wilkins brought Pratchett's computer hard drive to the Great Dorset Steam Fair, where a steamroller was driven over it. Two different steamrollers appear as prominent characters in the Thomas & Friends television series; George and Buster, both of whom are based on the Aveling Barford R class design.

The steamroller has a strong symbolism of an irresistible, onward pushing force. The Imperial Russian Army was nicknamed "steamroller" during World War One, as it was humongous by its size, and Russia initiated the war with an offensive. The "Russian Steamroller" is one of the personifications of Russia, along with the Russian bear, double headed eagle and Mat Zemlya.