We have developed a land-use/transport interaction model considering the environment based on urban economic theory and have implemented it to analyze the changes in accessibility resulting from road improvement. We have also analyzed whether such changes lead to a concentration or dispersion of population and industrial activities in a location. Our results also suggest that the interaction between transportation and landuse must be considered in the planning process, both corroboratively and theoretically. In particular, the results of the simulation showed that road improvements may increase the cost of travel because of the interaction between transportation and land-use, that is, induced traffic. Also, the results suggested that the non-interaction not to consider the interaction between transportation and land-use could cause us to overestimate benefits. In addition, we compared the effects of TDM with those by road building, carrying out a comparative analysis of the measured effects. The result of the comparative analysis demonstrated that TDM should be taken into account, as there is a considerable reduction effect with regard to the travel costs, the reduction effect for CO₂ and NO_X emission amounts is higher than it by road-building.