In this study, a rational overlay design method for flexible pavements in Arizona has been developed which includes roughness, fatigue and plastic deformation models. The method is incorporated in a microcomputer program which is also capable of analyzing the economics of other rehabilitation alternatives. During the development of the method, twenty in-service pavement sites were selected from Arizona highways covering various geographical and environmental regions, soil types, pavement conditions and traffic volumes. nondestructive tests (NDT) were performed on these sites using the Falling Weight Deflectometer at three stress levels as well as the Dynaflect. The pavement layers and subgrade moduli were backcalculated from NDT data using both static and dynamic analyses. The moduli of asphaltic layers were further adjusted for temperature. Statistical analysis was performed and the stress sensitivity was found to be small. Cone Penetration tests were further performed to verify the subgrade moduli. Asphalt concrete cores, base and subbase samples and undisturbed subgrade materials. In addition, base and subbase gradation as well as soil classification and Atterberg limits were obtained. The study expanded the data base for material properties in Arizona. This volume is the first in a three volume set. Volume II provides field testing procedure and workstation development and Volume III is a computer user guide.