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These prediction techniques can be used in pavement evaluation studies, as well as in forensic investigations. The MEPDG predicts individual performance measures (i.e., transverse cracking, fatigue, smoothness, rutting) based on site condition input for a given trial pavement section. The MEPDG models evaluate the impact of traffic, climate, materials, and subgrade stiffness on performance and account for the interactions among these components. All of the traffic loading defaults provided in the MEPDG, for example, were derived from the LTPP traffic database using WIM sites across the United States and Canada, and all of the distress and smoothness models in the MEPDG were calibrated using LTPP data. In fact, the MEPDG could not have been completed without the type and national extent of data provided by the LTPP studies. The LTPP database was critical to the development of the MEPDG, as it is the only source of comprehensive pavement data representative of national conditions. Development of the new guide required detailed information about pavements located across the country and representing a wide range of loading, climate, and subgrade conditions with varying structural compositions. Since the late 1990s, one of the pavement research community's single largest investments has been in the development of the MEPDG. The Mechanistic-Empirical Pavement Design Guide The LTPP program has also supported the implementation of, and advancements in, pavement management systems for agencies throughout the country. LTPP data have been used in numerous studies tasked with evaluating or developing design procedures, the most recent being the Mechanistic-Empirical Pavement Design Guide (MEPDG). An original LTPP objective was to acquire data for use in evaluating existing design methods and in developing new ones.