A road roller (also known as a roller-compactor or just roller) is a compactor-type engineering vehicle used in the construction of roads and foundations to compact soil, gravel, concrete, or asphalt. Similar rollers can also be found in landfills and agriculture. Regardless of its mode of propulsion, road rollers are usually referred to as steamrollers.
Road rollers either use the weight of the vehicle to compress the surface being rolled (static) or use mechanical advantage to compress the surface being rolled (mechanical advantage) (vibrating). On a road project, the initial compaction of the substrate is done with a padfoot or "sheep's foot" drum roller, which achieves higher compaction density due to the pads having less surface area. On large freeways, a four-wheel compactor with padfoot drum and a blade, such as a Caterpillar 815/825 series machine, would be used due to its high weight, speed, and the powerful pushing force to spread bulk material. On regional roads, a smaller single padfoot drum machine may be used.
The following machine is typically a single smooth drum compactor that compacts the high spots until the soil is smooth. To achieve a level surface, this is usually done in conjunction with a motor grader. A pneumatic tyre roller is sometimes used at this stage. These rollers have two rows (front and back) of overlapping pneumatic tyres, and the flexibility of the tyres provides a kneading action that seals the surface and allows the roller to operate effectively on uneven ground with some vertical movement of the wheels. The pad drum compactor is no longer used on the road surface once the soil base has been flattened.
The following course (road base) is compacted with a smooth single drum roller, smooth tandem roller, or pneumatic tyre roller in conjunction with a grader and a water truck to achieve the desired flat surface with the correct moisture content for optimum compaction. The smooth single drum compactor is no longer used on the road surface once the road base has been compacted (there is an exception if the single drum has special flat-wide-base tyres on the machine).
A paver is used to lay the final wear course of asphalt concrete (known as asphalt or blacktop in North America, or macadam in England) and a tandem smooth drum roller, a three-point roller, or a pneumatic tyre roller is used to crush it. On asphalt, three point rollers were once widespread and are still used, although tandem vibrating rollers are currently the preferred option. The kneading action of the pneumatic tyre roller is the final roller to seal the surface.
Rollers are sometimes used to compact landfills. Padfoot drums are common in these compactors, and they do not produce a flat surface. Due to the limited area contacting the ground, the cushions aid in compression.