要旨：This paper examines a conventional assumption of transport costs; any bilateral transport costs are symmetric. Using a comprehensive dataset on transport transactions in Japan, we first describe a directional imbalance of transport costs by transport mode and examine its potential sources such as density economies, long-haul economies, and a directional imbalance of transport flow. Based on the method of instrumental variables, we find that the density economies drive a deviation from symmetric transport costs between prefectures. We then develop a theoretical model of economic geography in which asymmetric transport costs occur in a transport sector for the density economies. Compared with the model without density economies, we show that agglomeration of economic activities is likely to emerge under any ranges of cost parameters. Thus, the economies of density in transport flows act as an agglomeration force.

要旨：In a closed monocentric city with three distinct land use patterns consisting of firms, condominiums and housing lots, we determine simultaneous optimization of regulations on building size, lot size and zonal boundaries under the existence of agglomeration externality in the business district and of traffic congestion externality in the residential zones. Results show that the optimal regulations are at most second best, and require not only downward adjustment to the market size of buildings at outer locations using maximum FAR regulation but also upward adjustment at more central locations using minimum FAR regulation within the business district, and similar regulations in the condominium zone, followed by a cap on the minimum lot size in the suburb. Moreover, the optimal city size is more compact than a market city, but whether the business district size should be compact or greater, depends on the relative level of agglomeration externality and the congestion. In addition, the boundary between condominium zone and housing lot zone does not need to be controlled.