Compactors, or rollers, are used to compress material, usually a bulk material. Asphalt compactors are required to compress asphalt, while soil compactors compress everything else. They are primarily used in road construction, and are among the cheapest vehicles in the game.
Official Description:Soil compactor are[sic] often used in subsoil preparation to compact the soil and thus leave particularly straight and stable construction surfaces. Asphalt compactor are [sic] functionally very similar, but are used for compacting fresh asphalt and are thus irreplaceable for road construction. The leisurely pace and articulated steering of a roller requires some familiarization, but allows for manoeuvrable and relaxed driving.
