The following are the various components of road surface
Top of the ground on which the foundation of a road rest is called sub grade. The level of the sub grade is decided by subtracting the total thickness of the pavement from the finished level of road pavement. Strength and durability of road depends on its sub grade.
When the bearing capacity of soil is poor and the intensity of traffic is high an additional layer is provided between soil and sub grade. This additional layer is called sub base.
The foundation of a road is called base. Thickness of base should be more than 30cm. the base coarse receives the impact of traffic through wearing coarse. The load of traffic is transferred to sub base and sub grade through base.
The super structure of road is called wearing course or road surface. it should be stable, durable and impervious. The wearing coarse may be laid in 1 or 2 layer according to the total design thickness and each layer should not exceed 10 cm. thickness of road surfacing depends upon type of traffic, intensity of traffic and type of material.