Calculation of life-cycle greenhouse gas emissions of urban rail transit systems: A case study of Shanghai Metro

In China, although per capita energy consumption is lower in the urban rail transit system than other modes of transportation, the total energy consumption and greenhouse gas emissions will reach considerable levels based on the current speed of urban rail transit system development. The objective of this research is to use the life cycle assessment (LCA) type method to define the system boundaries of the life cycle of Shanghai Metro and to inventory the associated resource inputs and emission outputs based on actual observed data. A comparative analysis of GHG emissions of different urban rail transit systems around the world is also provided. The results show that the total life-cycle GHG emissions per construction length of the entire Shanghai Metro are 109,642.81 t CO2e (with a service life of 50 years), and materials production, materials transportation, on-site construction, operation, and maintenance generated, respectively, about 4.1%, <0.1%, 0.4%, 92.1%, and 3.4% of the total emissions. Although the traction emissions per passenger-km traveled of Shanghai Metro are competitive at the global level, there is still great energy-saving potential in the operation phase, especially in ornately designed train stations. The preliminary conclusions of this study may help shed light on the emission reduction potential of urban rail transit systems and the emission reduction targets in China and serve as a source of information and data for future LCAs.