1. In geology, bare rock surface resembling a road, e.g. limestone pavement.

2. The floor of a coal seam.

3. In roadway construction, any material spread on the subgrade to distribute load and protect against erosion and traffic wear. The types of material used and thickness depend on the type and use of road. Generally the pavement has four layers. (a) The wearing course is the top layer of the carriageway. It must be durable, impermeable, skid-resistant, and resistant to polishing. On the most heavily trafficked roads the polished stone value (PSV) (see aggregate tests) must exceed 60%. The wearing course lies on a surface provided by the basecourse. (b) The basecourse is a layer of gravel or crushed rock (aggregate) of specific dimensions to provide drainage, distribute load on to the road base, and protect against freezing. (c) The road base provides the main load-bearing foundation or ballast and consists of irregular-sized rock aggregate, either bonded or loose. (d) The subbase is a layer of coarse aggregate below the road base. It provides extra support or drainage. In cold climates large pore spaces are necessary to prevent water rising by capillary action, leading to the collapse of the structure after thawing. (e) The subgrade is the rock or subsoil on which the subbase is laid.