The degradation and the damage state of a flexible pavement section may be attributed to several factors. These include environmental factors, traffic loading factors, and material interaction and variability factors. The collective conditions of a pavement section in a particular damage state may be called pavement damage index (PDI). Such a damage index is related to the pavement deflection output.

This paper discusses the characteristic parameters of the pavement time-dependent deflection response and their relationship to the damage done to the flexible pavement section in question. Further, a case study is presented where a full-depth asphaltic highway pavement section was tested after construction and before it was subjected to any traffic loading. The calculated characteristic parameters of the time-dependent deflection response indicated, at the time, that a severe damage in the form of permanent deformations (rut depth) should be expected when the pavement section is opened to traffic. The highway section in this case study experienced a rut depth of up to 25.4 mm (1 in.) after only six months of mixed traffic (trucks and cars).