Impacts of Transport Infrastructure Policies in Population-Declining Metropolitan Area

In The Tokyo metropolitan area, population growth and economic growth have caused serious urban problems like sprawl at urban fringe, heavy congestion not only in road network but also in railway network, environmental emission and so on. Although there still now remain the difficult problems for us to tackle with, the transport infrastructure policies until today have succeeded in sustaining the high business productivity with high spatial agglomeration and quality of life in the population-growing trend. Japan is however now at the down-slope of the population trend curve and Tokyo is predicted to begin a decade-long decline in population. The significant population decline in Tokyo metropolitan area is an inexperienced situation for the people and policy makers. They may be concerned that the population decline would reduce the great merit of spatial agglomeration in Tokyo. The question at the heart of policy discussion is how we can sustain the high level of business productivity and quality of life in the Tokyo metropolitan area by spatial restructuring. This paper has developed the Computable Urban Economic Model, which re-formalizes the conventional landuse-transport interaction model on the basis of microeconomic foundation, so as to answer the above question. As a result, we found that the central Tokyo remains as the center of the economy in 2050 with high spatial agglomeration since the agglomeration is accelerated by the scale economy. On the other hand, population which is not affected by agglomeration, is decreasing at each zone with the same level. The investment to the three Ring Roads is expected to contribute to developing more dispersive urban structure since the three Ring Roads increase the transportation convenience at the suburb and it induces to the entry of the firms and population as well. This does not, however, the central Tokyo loses its competitiveness but they still remain strong in terms of the spatial distribution of the firms. The reduction of population mitigates the congestion of the road network. It enables us to increase our convenience in terms of the trip by car. It induces to more trips to the households and business people, which bring about more communication, that is one of the keys for the productivity growth and the enhancement of households’ utility. During this period, traffic density of car increase due to the enhancement of the transport convenience by car.