Models developed to predict reflective cracking in flexible pavement overlays do not explicitly incorporate the combined effect of the cracked and uncracked areas in the original pavement. This affects the development of cracks in the overlay. Therefore, a model is needed that will incorporate this factor explicitly, making predicting of cracking in pavement overlays more realistic in pavement management systems and pavement reliability. A mechanistic approach based on fracture mechanics with an empirical stochastic form to develop the desired model is presented. This approach has been adopted because the new design trends (such as the new 2002 AASHTO design guide) will follow a more mechanistic approach than the current trends. In addition, this approach is lacking in the literature for data of in-service roads. The use of the developed model for the study of crack initiation is presented. Data obtained from the Florida Department of Transportation are divided into Interstates and arterials. The results show that the proposed model predicts the observed cracking with an R 2 of 0.72 for the Interstates and 0.40 for the arterials. Because the exact time of crack initiation is not recorded, the observed crack-initiation time is approximated by the last time no cracking was observed (i.e., right before cracking was first recorded). The proposed methodology predicts the crack-initiation time with an average absolute error of 18.6 percent.