Since the Ohio Department of Transportation (ODOT) has adopted the AASHTO design equations for new pavement design, it was considered needful to conduct a research study that would determine the deviations in traffic and performance prediction parameters and the overall standard deviations applicable to Ohio conditions. Pavement test sites were selected to represent the statewide distribution of pavement designs in Ohio, characterized by such factors as material type, functional classification, and different climatic and soil regions. Continuous traffic data collection was accomplished by the use of weigh-in-motion devices. Pavement serviceability index (PSI) was measured by Ohio noncontact profilometer. Core samples were obtained and several laboratory tests were conducted to determine the as-constructed material properties and variability of the design input parameters. Comparison of predicted and observed performances based on approximately four years of data indicated that AASHTO equation does not predict the performance of flexible pavements in Ohio.