Pavements are designed, constructed, and maintained to provide adequate support for loads imposed by traffic, and to provide a uniformly firm, stable, smooth, all-weather surface. To achieve these objectives, the subgrade, base, underdrainage and pavement must function together properly so that the pavement will not fail under the predicted traffic loads. Pavements are either flexible or rigid.
Flexible pavements consist of a mixture of liquid asphalt and aggregate. There are three general categories of asphalt pavement design. Selection is based on traffic volume.