Heavy-weight truck loading is one of the main causes of rapid flex- ible pavement deterioration. At the tire–pavement contact area, truck tires produce highly nonuniform vertical contact stresses as well as sur- face transverse and longitudinal tangential stresses (1). It has recently been shown that surface tangential contact stresses highly affect pave- ment responses near the surface, and these responses diminish as the depth increases. The three-dimensional (3-D) contact stresses result in a complex stress state near the pavement surface. This increases pave- ment damage potential, including top-down cracking, near-surface cracking, and hot-mix asphalt (HMA) rutting (2, 3). Vehicle loading is commonly modeled as static; the pavement is actually subjected to moving wheel loads, which are loading time dependent. The pavement structural dynamic response, or dynamic amplification, depends on the ratio of external loading frequency to the structural natural frequency. The natural frequency for flexible pavement ranges from 6 to 12 Hz (4, 5). Gillespie et al. found that truck loading frequency is about 4.6 Hz at a speed of 58 km/h and 6.5 Hz at 82 km/h (6). Therefore, dynamic analysis is important for some loading conditions. Cebon (7 ) suggests that the dynamic component of a wheel load may increase the fatigue damage by four times and rutting damage by at least 40%. Even for smooth pavement, the pavement response increases 10% to 15% under a dynamic load. Yoo and Al-Qadi (8) reported that pavement response from dynamic analysis was usually higher than from quasi-static analysis; especially at high speed and low temperature. Under these conditions, the loading frequency and the pavement’s natural frequency are near its resonant state. There- fore, to consider the dynamic loading effect on flexible pavement responses, this study includes the implicit-dynamic analysis in regard to transient time-dependent dynamic tire loading. To accurately predict pavement response, proper material charac- terization is also needed. Flexible pavements are commonly modeled as multilayer linear elastic systems; the theory was originally devel- oped by Burmister in 1943 for two-layered linear elastic systems (9). However, hot-mix asphalt (HMA) behaves as a viscoelastic material because its response to induced loading or deformation depends on temperature and loading time. In this study, indirect creep compliance tests were conducted to characterize the HMA viscoelastic properties. Considering that all the aforementioned components are necessary to accurately predict pavement response, a 3-D finite element (FE) model using implicit-dynamic analysis was developed. The analysis incorporated measured tire–pavement contact stresses, continuous moving load, and HMA viscoelastic properties. The developed model was used to predict pavement responses under moving loads for var- ious full-depth flexible pavement systems exposed to various tire configurations. The developed model has been validated using measurements from accelerated loading testing. Dynamic Analysis and In Situ Validation of Perpetual Pavement Response to Vehicular Loading Imad L. Al-Qadi, Hao Wang, Pyeong Jun Yoo, and Samer H. Dessouky 29 A three-dimensional (3-D) finite element (FE) model was developed to predict pavement responses to vehicular loading. The model incorporates measured tire–pavement contact stresses, continuous moving wheel load- ing, and hot-mix asphalt (HMA) viscoelastic characteristics. The model was fine-tuned using implicit-dynamic analysis and validated using pave- ment response from accelerated loading. Two tire configurations (dual- tire assembly and wide-base 455 tire) and three full-depth flexible pavement designs (HMA 152 mm, 254 mm, and 420 mm) were used in both FE modeling and accelerated loading tests. The predicted and calcu- lated strain responses at the bottom of HMA were in agreement. Most important, the study shows that vertical shear strain in the upper 76 to 100 mm of the pavement surface is critical for thick pavement and is influ- enced by the 3-D tire–pavement contact stresses under each tire rib. How- ever, the tensile strain at the bottom of HMA is affected mainly by the total wheel load. The vertical shear strain is responsible for near-surface fatigue cracking as well as HMA primary rutting. Top-down cracking could result from the local vertical shear strain in the upper 25 mm of the HMA where the effect of tire–pavement tangential stresses are the high- est. In addition, the study concluded that wide-base tires cause higher lon- gitudinal tensile strain at the bottom of HMA and compressive strain at the top of subgrade, where those responses are highly affected by the total wheel load. However, wide-base tires were found to cause less vertical shear strains near the surface than dual-tire assembly loading regardless of HMA thicknesses. Most methods of flexible pavement analysis predict pavement responses using uniform tire–pavement contact stresses, circular contact area, and stationary vehicular loading. Unfortunately, these assumptions are inconsistent with realistic loading conditions and may result in erroneous pavement response calculation and pavement performance prediction. However, pavement response prediction may be established using an analysis approach that simulates accurate tire–pavement interaction and incorporates appropriate pavement material characterizations. I. L. Al-Qadi, Illinois Center for Transportation, and H. Wang, Department of Civil and Environmental Engineering, University of Illinois at Urbana–Champaign, 205 North Mathews MC-250, Urbana, IL 61801. P. J. Yoo, Korea Institute of Construction Technology, 2311 Daehwa-Dong, Ilsan-Gu, Goyang-Si, Gyeonggi-Do, Korea 411-712. S. H. Dessouky, Advanced Transportation Research and Engineer- ing Laboratory, Department of Civil and Environmental Engineering, University of Illinois at Urbana–Champaign, 1611 Titan Drive, Rantoul, IL 61866. Corresponding author: I. L. Al-Qadi, alqadi@uiuc.edu. Transportation Research Record: Journal of the Transportation Research Board, No. 2087, Transportation Research Board of the National Academies, Washington, D.C., 2008, pp. 29–39. DOI: 10.3141/2087-04