Laboratory fatigue testing of asphalt concrete can be used to predict field performance. The introduction of a shift factor is necessary to account for the effects of residual stresses and healing that occur in the field but do not occur in the laboratory. In this study the healing mechanism in asphalt concrete is investigated. A theoretical hypothesis for the shift factor and a new approach to characterizing the toughness of paving mixtures based on the J-integral concept are also introduced. The shift factor is assumed to consist of the combined effect of a strain recovery component and crack recovery component. The two components can be determined from simple laboratory tests, including stress relaxation, beam fatigue, and the overlay tests. The fracture mechanics approach, the J*, is based on the path-independent J integral, which can be defined as the energy released per unit area of crack extension. The J* parameter is adopted to characterize material toughness.