A Road roller (sometimes called a roller-compactor, or just roller) is an engineering vehicle used to compact soil, gravel, concrete, or asphalt in the construction of roads and foundations.
In many parts of the world, road rollers are still known colloquially as steam rollers, regardless of their method of propulsion. This typically only applies to the largest examples (used for road-making).
The first road rollers were horse-drawn, and were probably just borrowed farm implements.
Since the effectiveness of a roller depends to a large extent on its weight, self-powered vehicles replaced horse-drawn rollers from the mid 1800's. The first such vehicles were steam rollers, and, in the UK, these remained in commercial service until the early 1970's.
As internal combustion engine technology improved during the 20th century, petrol- and diesel-powered rollers gradually replaced their steam-powered counterparts, and virtually all road rollers in commercial use now use diesel power.
Road rollers work by using the weight of the vehicle to compress the surface being rolled. Initial compaction of the substrate is done using a pneumatic-tyred roller, where instead of the single- or double-drum is replaced by two rows (front and back) of pneumatically filled tyres. The flexibility of the tyres, with a certain amount of vertical movement of the wheels, enables the roller to operate effectively on uneven ground. The finish is done using metal-drum rollers to ensure a smooth, even result.
Rollers are also used in landfill compaction. Such compactors typically have knobbly ('sheeps-pad') wheels and do not attempt to achieve a smooth surface, merely a squashed one.
The roller can be a simple drum with a handle that can be operated by one man, and weighs 100 pounds, all the way up to a massive ride-on road roller weighing 21 short tons (44,000 lb or 20 tonnes) and costing more than $150,000 US dollars. A landfill units can weigh 59 short tons (54 tonnes). On some machines the drums may be filled with water.