Fatigue data from the AASHO Road Test were plotted for each level of serviceability. The Kentucky thickness design system uses the concept of a variable level of serviceability as a function of EALs. The Kentucky thickness design curve for the equivalent CBR was converted to an equivalent structural number and superimposed on each of the specific serviceability figures. The AASHTO Equation C–14 of the 1972 AASHTO Interim Guide was evaluated for each level of serviceability and superimposed on its respective figure. Equation C–14 fits reasonably well for serviceability levels of 2.0 and 2.5 but does not fit the remining serviceability levels. the Kentucky thickness curve is asymptotic to a portion of each figure and directly related to level of serviceability. Figure 6 is a composite of portions of Figures 1 through 5 created by lifting the portion of each level of serviceability for which the Kentucky thickness design curve was asymptotic to the data for specific range in EAL. The composite figure illustrates the potentiality of the AASHTO design method being expressed by one nomograph (not developed or shown herein) in which the serviceability level increases as EAL increases.

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The contents of this report reflect the views of the authors who are responsible for the facts and accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the University of Kentucky nor the Kentucky Transportation Cabinet. This report does not constitute a standard, specification, or regulation.