Evaluation of subway systems in CO 2 emissions: Comparative analysis of emissions from cars, buses and subways

ABSTRACT The transportation sector is responsible for a portion of the global emissions of carbon dioxide (CO2). Scientific studies published on CO2 emissions by passenger transport systems treat basically results involving only the emissions related to fuel consumption of cars and buses. As for subways, usually emissions related to the generation of electrical energy needed to provide the traction force of the trains are considered. No specific or standardized publications on other approaches to calculate emissions for subways were identified. Thus, this study aims to provide a scientific contribution to the general study of CO2 emissions by subways, conceptually defining five approaches of calculations and conducting a comparative analysis of CO2 emissions by cars, buses and subways. The result of this research allowed to quantify the actual contribution of subways on the reduction of total emissions from the transportation sector. In the traction power of trains approach, it was concluded that the subways of São Paulo and Rio de Janeiro emit 63.5 times less than cars and 8 times less than buses.

摘要 交通运输行业是全球二氧化碳（carbon dioxide）排放的重要贡献来源之一。目前已发表的客运系统二氧化碳排放相关科学研究，其核心结论基本仅覆盖乘用车与巴士的燃料消耗关联排放。针对地铁系统，现有相关研究通常仅考量为列车提供牵引力所需的电能生产环节所产生的排放。目前尚未发现针对地铁系统碳排放其他计算方法的专门性或标准化研究成果。为此，本研究旨在为地铁系统二氧化碳排放的系统性研究提供科学支撑：从概念层面界定五种计算方法，并对乘用车、巴士与地铁的二氧化碳排放开展对比分析。本研究成果可量化地铁系统对交通运输行业总排放的实际减排贡献。在列车牵引电能计算方法框架下，研究得出圣保罗与里约热内卢的地铁系统排放量仅为乘用车的1/63.5、巴士的1/8。