The permanent deformation of the asphalt concrete (AC) layer is a major distress that has a direct effect on road safety. Researchers have attempted to predict the permanent deformation of roads by testing asphalt mixture specimens in laboratories. One of the candi- date tests for the measurement of permanent deformation is the flow number test performed with the simple performance tester (SPT). This test measures the permanent strain and the number of cycles to failure. Another means of estimating permanent deformation is by the use of predictive models. A number of predictive equations have been developed on the basis of the permanent deformation data col- lected in laboratories. Among these equations are the two NCHRP Project 1-37A (NCHRP 1-37A) equations that are included in the Mechanistic–Empirical Pavement Design Guide (MEPDG) software. The intent of the study described here was to examine different means of measuring and estimating permanent deformation or rutting. Comparisons of the measured and predicted permanent deformation should reveal to some extent the validity of the predictions. The asphalt pavement lanes of the Accelerated Loading Facility (ALF) of FHWA were tested for rutting before loading and after specific cycles of loading. During the construction of the lanes, loose asphalt mixtures were taken from each section and compacted in the laboratory. These samples, which are referred to as plant-produced specimens compacted in the laboratory (PP specimens), were subjected to dynamic modulus and flow number tests with the SPT. The rutting of the asphalt mixture layers of the ALF lanes was pre- dicted by using Level 1 and Level 3 analyses with MEPDG software by using the detailed data that are available for the ALF lanes. The models in MEPDG, which are referred to as NCHRP 1-37A perma- nent deformation models, were also used separately to determine the effect of stiffness on the prediction of permanent deformation. OBJECTIVES The main objectives of this study were 1. To estimate the asphalt rutting of ALF sites by using MEPDG software and NCHRP 1-37A permanent deformation prediction models, 2. To compare the predicted pavement rutting with the rutting measured at the ALF sites, 3. To compare the permanent strains measured during the flow number test with the rutting measured at the ALF sites, and 4. To validate existing MEPDG software rutting predictions with data collected from the ALF and to evaluate the NCHRP 1-37A asphalt mixture permanent deformation models used in MEPDG software. Verification of Rutting Predictions from Mechanistic–Empirical Pavement Design Guide by Use of Accelerated Loading Facility Data Haleh Azari, Alaeddin Mohseni, and Nelson Gibson 157 As a part of FHWA’s Accelerated Loading Facility (ALF) experiment, asphalt pavement lanes were built with six different asphalt binder types and two different thicknesses and were tested for rutting and fatigue cracking. Loose asphalt mixtures were taken from each lane at the time of construction and compacted in the laboratory. These plant-produced specimens compacted in the laboratory and other laboratory-produced specimens were subjected to dynamic modulus and flow number tests with a simple performance tester (SPT). Field rutting measurements of the ALF lanes were conducted during and after the loading. A good agreement between the permanent strains measured by the flow number test and the ALF rutting measurements was observed for the initial rutting. The rutting of asphalt mixture layers of the ALF lanes was also predicted by using Level 1 and Level 3 analyses with Mechanistic– Empirical Pavement Design Guide (MEPDG) software by using the detailed data that were available for the ALF lanes. Comparison of the predicted rutting with the rutting measured on the ALF indicated that the rutting predicted by Level 3 analysis with MEPDG software, based on the asphalt stiffness equation, agreed somewhat with the actual rut- ting on the ALF lanes. However, the rutting predicted by Level 1 analysis, based on the actual SPT-measured dynamic modulus, significantly over- predicted the amount of rutting. The NCHRP Project 1-37A permanent deformation prediction models used in MEPDG software were also used separately to predict the rutting of the ALF lanes by using the predicted and the measured stiffness values. Results similar to those obtained by Level 1 and Level 3 analyses with MEPDG software were obtained. The overprediction of rutting by Level 1 analysis with MEPDG software may be related to the calibration of the NCHRP Project 1-37A per- manent deformation equation. The model seems to have been cali- brated by using the stiffness predicted from the NCHRP Project 1-37A equation, which is proven to overpredict stiffness at high tem- peratures, rather than the tested SPT stiffness and, thus, can provide reasonable rutting estimates only for Level 3 analyses (by use of the predicted stiffness). H. Azari, Research Program, AASHTO Materials Reference Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Stop 8619, Gaithers- burg, MD 20899. A. Mohseni, PaveSys Inc., 6105 Maiden Lane, Bethesda, MD 20817. N. Gibson, FHWA, HRDI-11, 6300 Georgetown Pike, McLean, VA 22101. Corresponding author: H. Azari, hazari@amrl.net. Transportation Research Record: Journal of the Transportation Research Board, No. 2057, Transportation Research Board of the National Academies, Washington, D.C., 2008, pp. 157–167. DOI: 10.3141/2057-19