China's high-speed rail (HSR) system has been connecting cities and powering economic growth. Travelling in the “bullet train” with over 300 km/h speed and experiencing the efficient commuting, I was wondering, what will this marvel of modern engineering leave its mark on the environment through the extensive use of construction materials and greenhouse gas emissions? In a recent study published in Communications Earth & Environment, we delve deeper into its material metabolism and environmental footprint. Our aim is to shed light on the sustainability challenges posed by the rapid expansion of China's HSR network.

Building the Giant:

China's HSR network has witnessed unprecedented growth. In just over a decade, it expanded from 1,039 kilometers in 2008 to a staggering 38,914 kilometers by 2020. This rapid expansion, driven by urbanization and economic development, required immense construction materials. The cumulative material stock skyrocketed from 0.13 gigatons in 2008 to 3.65 gigatons in 2020, with a projected increase to 4.9 gigatons by 2035.

The majority of these materials consist of nonmetallic minerals like gravel, sand, and cement, comprising 88% of the total stock. Bridge and subgrade components dominate, with bridge stocks increasing substantially due to the emphasis on continuous seamless rails and large-span tunnels.

Technological Innovations and Sustainable Materials:

Interestingly, as HSR speed increased, construction technology innovations offset material demands. HSR stock density decreased, with HSR material densities falling from 110 t/m in 2008 to 92 t/m in 2020, despite an increase in operational speed. Long-span box girders and ballastless tracks played a significant role in reducing material consumption.

Bridging the Gap Across Chinese Provinces:

HSR is touted as a catalyst for regional development, bringing cities closer and reducing transport costs. Spatially, we observed a narrowing gap in material distribution across Chinese provinces. While the East and Central regions initially held the lion's share of material stocks, Western regions have witnessed substantial growth, bridging the inequality gap. However, the divide along the Hu-Line, separating China into two halves, still needs addressing.

Material Flows and Sustainability:

Our analysis of material flows in HSR construction revealed substantial resource demands for gravel, sand, and cement. This raises concerns about the impact on resources such as sand, potentially contributing to issues like coastline erosion and ecosystem degradation. We also noted a significant amount of waste generated in HSR construction, emphasizing the need for circular economy principles in waste management.

Emissions and Decarbonization:

To understand the environmental impact comprehensively, we compared material stocks, carbon replacement value (CRV), and operational greenhouse gas emissions across different passenger transport infrastructures, including HSR, road, and aviation. While HSR's material stocks are smaller than those of roads, the CRV emissions showed potential challenges due to energy-intensive materials like steel and cement.

Despite its operational emissions, HSR still outperforms road transport in terms of environmental impact per passenger turnover. However, the rapid expansion of HSR has led to increasing operational emissions. We suggest adopting cleaner energy sources and logistical improvements to mitigate emissions.

In conclusion, China's HSR has brought about tremendous advancements in transportation but also posed significant environmental challenges. Our study sheds light on the material metabolism, spatial distribution, and sustainability of this iconic infrastructure, offering insights for policymakers and stakeholders to navigate the road toward greener transport systems.

This research has been published in Communications Earth & Environment and is available online (https://doi.org/10.1038/s43247-023-00972-6). All data associated with the research is available at https://doi.org/10.6084/m9.figshare.23790294. For further information, please contact eastdawn@tsinghua.edu.cn or maoruichang@gmail.com.