Since the 3rd edition of Road Note 29 was published in 1970, further information on road performance has been obtained and there have been important advances in research on materials, methods of construction and mathematical models of pavement behaviour. These advances have been used to develop a new method for experimental roads interpreted in the light of structural theory. The capping layer and sub-base is designed primarily as a construction platform. Design curves are given for the thickness of bituminous, lean concrete or wet-mix roadbase required to carry the traffic expected to use the road during its design life. The design method offers the means of adapting proven designs to take advantage of new materials, new design configurations and construction methods