An artificial surface laid over the ground to facilitate travel. In this article only road pavements are discussed. The engineering involved is closely similar to that for airport surfacing, another major type of pavement. A pavement's ability to support loads depends primarily upon the magnitude of the load, how often it is applied, the supporting power of the soil underneath, and the type and thickness of the pavement structure. Before the necessary thickness of a pavement can be calculated, the volume, type, and weight of the traffic (the traffic load) and the physical characteristics of the underlying soil must be determined.