Welded residual stress and stochastic traffic at the deck-to-rib welded joints in the orthotropic steel deck (OSD) of bridges highly affects the fatigue life of bridges. This study presents a strain energy-based method to evaluate the service life of welded joints in the OSD considering the combined effects of traffic load and welded residual stress. Thermomechanical analysis is performed for the welding process of the welded joints using a finite-element model to analyze the distribution of welded residual stress at critical locations of the welded joints. An analysis model is developed to simplify the nonlinear superposition of vehicle-induced stress and welded residual stress. A modified strain energy-based fatigue evaluation approach is presented based on the superposition of stresses. Based on the presented model, a new W_a–N_f curve is proposed to take the effects of welded residual stress into consideration. The presented method is validated against experimental results, and then it is applied to investigate the fatigue life of welded joints in an in-service cable-stayed bridge. The theoretical and inspection results are compared and analyzed. The results show that there is a better coincidence between the predicted fatigue life using the presented approach and the inspected fatigue life in contrast with the conventional approach of neglecting the effects of welded residual stress.