Abstract
Urban subway system, as an important type of urban transportation infrastructure, can provide mass mobility service and help address urban sustainability challenges such as traffic congestion and air pollution. The continuous construction of subways, however, causes large amounts of construction materials and embodied greenhouse gas (GHG) emissions. In this study, we characterized the patterns of subway development, construction material stocks, and embodied emissions covering all 219 cities in the world in which subways are found by July 2020. The global subway length reached 16,419 km in 2020, and the construction material stocks amounted to 2.5 gigatons, equaling to an embodied emission of 560 megatons. In particular, China’s subway system contributes to ~40% of the total global stocks, with a pattern of moderate and steady stocks growth before 2010 and a rapid expansion afterwards, implying the late-development advantages and infrastructure-based urbanization mode. Our results demonstrated that identifying the spatiotemporal characteristics of subway materials stocks development is imperative for benchmarking future resource demand, informing sustainable subway planning, prospecting urban mining and waste management opportunities and challenges, and mitigating the associated environmental impacts for global GHG emission reduction.
Highlights
Transportation infrastructures provide connectivity and mobility services to modern societies
Transportation networks have already occupied over 25% of the global urban built-up area (May, 2013)
Due to the long lifetime of subways and for safety and/or heritage reasons, only a small share of the subway built-in materials are potentially available as secondary resources (e.g., 3% for Vienna’s subway network within 100 years) (Lederer et al, 2016a), leading to both challenges and opportunities for urban mining and waste management at the end of subway service life
Summary
Transportation infrastructures provide connectivity and mobility services to modern societies. They are essential for ensuring human development and addressing sustainability challenges (Wann-Ming, 2019; Thacker et al, 2019). Subways were constructed and operated firstly in Europe (1863 in London) and North America (1892 in Chicago) in the late nineteenth century. Since it has developed rapidly worldwide, especially for cities in developing countries such as China and India in the past decade (UITP, 2018). Understanding the development patterns and accumulated material stocks of subways is essential to estimate future resource demand, waste generation, recycling potentials, and identify effective environmental mitigation strategies for sustainable urban subway planning and management
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
