Estimating Additional Mass Transit Needed to Reduce Carbon Dioxide Emissions from Regional Passenger Transport in Japan

This study aims to estimate the necessary scale of additional mass transit on trunk lines to reduce carbon dioxide (CO2) emissions from regional passenger transport in Japan. First, a local transport region is defined as an area within which most daily transport is conducted. In each region, the target of CO2 emissions from local passenger transport activities in 2050 is set to 20% of those emissions in 2000. The amount of CO2 exhaust from local passenger transport can be estimated on the basis of technological innovation; thus, the amount of reduction needed to achieve the target can be calculated. Second, changes in CO2 emissions from the introduction of a mass transit system are evaluated, considering their reduction from replacing private vehicles and the emissions from constructing and operating the mass transit system. For this purpose, life-cycle assessment is applied. The total amount of CO2 emissions from infrastructure construction, vehicle production, and operation from mass transit is calculated. The transport density of each route is estimated with population density in a densely inhabited district of each local transport region. The transit system that emits the least CO2 per passenger kilometer is selected. The extent of new services needed to achieve the CO2 reduction target is calculated. A series of calculations provides the lengths of additional mass transit routes required to reduce traffic volumes sufficiently to achieve the CO2 reduction target for local passenger transport by 2050.