Flexible and composite pavement
The main purpose of the road structure is to provide a means of reducing the stress or pressure due to a wheel load to a value which the ground under that structure can support. The intensity of the static and dynamic stress is greatest at the surface of the road and spreads in a pyramidal shape throughout the depth of the structure. As the stresses from the vehicles travelling the road are greater nearer the surface, stronger materials are needed in the surfacing than in the lower layers. Information for pavement design for roads in the United Kingdom is provided by Highways England and its research establishment, the Transport Research Laboratory. The use of dense binder course materials can add considerable strength to an existing road, their use is particularly appropriate for strengthening a road which may be required to carry heavy traffic at short notice.