Road Note 29 (RN29) takes account of increasing axle loads and vehicle
numbers while also differentiating between the performance characteristics of
different roadbase materials. (The roadbase is assumed to satisfy the entire
strength requirements for the entire pavement, with the surfacing considered to
make no significant contribution to the strength of the pavement. The primary
function of the surface material is to provide surface texture and regularity.) The
RN29 procedure is best explained as a series of design steps.