In this paper, a revised four-stage traffic plan method is proposed to estimate the post-earthquake traffic flow assigned to a road network. We also suggest a post-earthquake road capacity estimation method that considers the seismic vulnerability of structures and the potential building collapse area that might occupy a road after a major earthquake. Through an analysis of the "randomicity" of traffic demands (traffic flow) and road capacities after an earthquake, and depending on reliability theory, the "unblocked" reliability of road segments and the reliability of the entire transportation network can be estimated using techniques presented in this paper. Through the component importance analysis, the optimum improvement and thus, optimum recovery plan for a transportation system that focuses on alleviating earthquake indirect losses is suggested. At the end of this paper, an example is given to illustrate the application of the unblocked reliability index in post-earthquake traffic condition estimation and in developing earthquake response strategies for urban transportation systems.