The equilibrium between land use and transportation system has been an important issue in the city planning. Transportation Impact Assessment is a measure to make the equilibrium by balancing the relationship between urban development and transport facilities. First, this paper discusses about the development patterns which do not cause the road congestion in a hypothetical city with grid type network structure. By using a traffic simulation model, NETSIM, maximum value of floor area ratio (FAR) to avoid congestion is calculated in various situations. The result shows allowable level of FAR is much underestimated than the current legal limitation level considering the existing road capacity. Next, the model was applied to the actual city area with the existing road network. After constructing network of wider city area in computer model, we simulate the traffic impact generated by new development in the CBD. It was found that road congestion due to the new development is observed not only on immediately surrounding road but also in much wider area in the city, because of the change of the shortest path demanded by other traffic flows.