A pavement provides a functional surface for safe operation of a vehicle. The operator or passenger of a vehicle does not particularly care about the material from which the pavement structure is constructed. However, they are sensitive to such factors as speed, safety (skid resistance), and comfort (roughness). One aspect of pavement design is the selection of the thickness of the pavement and its various components sufficient to support vehicular loadings and to transfer those loadings

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... successive layers of the pavement - surface, base, and subgrade - to the soil on which the pavement rests. The structural design of a highway pavement involves a study of the soils, paving materials, and their behavior under load. The pavement must be adequate to support the wheel loads of motor vehicles. Each time a vehicle passes over a pavement, some stressing and straining of the surface and underlying layers occur. If the load is excessive or if the supporting layers are not sufficiently strong, repeated applications of the vehicular loadings will cause rutting and cracking that ultimately lead to a complete structural failure of the pavement. The pavement thickness design scheme suggested in this report provides a procedure by which the load-carrying capabilities of any individual layer or of the soil upon which the pavement rests are not exceeded.