The objective of this study is to evaluate five scenarios for extending the Japanese transport infrastructure by combining a few service levels of the highway network with Shinkansen and airport infrastructures. This evaluation considers the impact in terms of variations in CO₂ emissions, energy consumption, and travel time.

In the five scenarios, trip generation, distribution, and modal splits were estimated for the future using a macro-forecasting model built in this study. Further, the environmental impacts due to the construction and operation of such infrastructures were estimated using the embodied energy and emission intensity data for Japan.

The results predict increases in the energy consumption and CO₂ emissions in the next 30 years. On the other hand, the travel time decreased in all the scenarios; in particular, the scenario that considers the complete extension of the highway network exhibited the lowest travel time.

Based on monetary analyses, the losses due to the higher energy consumption and CO₂ emissions are compensated by the reduction in the travel time.

Finally, this study demonstrates that, devising a construction plan by combining highway and Shinkansen networks would reduce the travel time, CO₂ emissions, and energy consumption. These advantages would be especially evident in the metropolitan area and regional areas that are not provided with high-speed transportation infrastructures.

In Japan, financial balances in rural areas are being adversely affected because public incomes are decreasing due to the decrease in the youth population, while administrative expenditures for older people are increasing. In order to decrease the per capita cost, we recommend that local governments should be consolidated to enable the sharing of the fixed cost involved in labor and facilities for public services. Previous studies regarding consolidation suggest an “optimal population size” corresponding to the lowest per capita cost. However, the influence of socio-demographic and geographic features, such as the average distance between an administrative office and inhabitants, road network, and land altitudes representing the elevation of an area have been ignored to date while planning consolidations. This study aims to estimate the influence of socio-demographic and geographic features on the administrative expenditure by the stochastic frontier model. Since the per capita cost significantly varies between cities and other places (towns and villages), we analyzed two models: one for each type of government. Our results revealed that these features significantly influence the expenditure. Therefore, while planning consolidations, the location of the administrative office should be carefully selected in order to minimize the average distance from inhabitants; further an adequate road network is essential.