LR1132 was based on observations of highways over a 20-year period. Later
research (Munn et al., 1997) indicated that cracking and deformation is more
likely to occur in the surfacing than deeper in the structure. Therefore, it was
surmised that a well-constructed flexible pavement would have a very long structural life provided such signs of distress are treated before they affect the structural integrity of the highway. HD 26/01 notes that, for long-life flexible
pavements designed to carry traffic for at least 40 years, it is not necessary to
increase the thickness of the pavement beyond that required for 80 million
standard axles