The purpose of this research is to develop a methodology to interface transportation planning and traffic simulation. Differences in representations of planning and traffic networks prohibits planners and engineers from sharing the input data for the same area being studied. Therefore the planning data need to be utilized to create data that the traffic engineers can use for traffic simulation, thus avoiding duplication of effort to collect data for the two purposes. The methodology developed specifically for the Urban Transportation Planning Software (UTPS) and Traffic Simulation Software (TRAF), can be modified to interface planning and simulation performed by other software as well. The methodology is demonstrated using a typical urban town network.