The top-down crack (TDC) is one of the critical damage mechanisms that significantly reduce the life expectancy of asphalt pavement layer in an orthotropic steel deck (OSD) system. The fracture behavior associated with TDCs in OSD pavements appears to be more complicated than that in road pavements. In this research, the major types of TDCs are to be developed by cautious examination of the strain fields in an uncracked OSD pavement system. A three-dimensional finite element fracture model is then to be constructed to study fracture responses in cracked OSD pavements with possible appearance of these types of TDCs. The associated stress intensity factors are to be predicted by implementing a specific contour integral and feasibility of the calculation is to be verified by a series of deliberate demonstrations based on a number of numerical features. The verified fracture model is to be applied to conduct a number of sensitivity analyses to investigate the influence of complicated geometric, loading, and environmental effects in an OSD pavement system subjected to heavy mixed-mode vehicular loadings.