Since the late 1990s, the Yangtze River Delta (YRD) has experienced profound growth in economic scales and urban size. However, it is still unclear how much energy is consumed from both fossil fuel and electricity usage for transportation sectors (TCO₂). We take 10 sampled cities in the YRD as examples and examine their city-level sustainable levels from 1990 to 2018. Then, we observed that SHSN (Shanghai, Suzhou, Nanjing) are in leading positions, followed by WCN (Wuxi, Changzhou, Ningbo) and NXH (Nantong, Xuzhou, Hefei). We found that the cumulative TCO₂ in SHSN from 1990 to 2018 is the highest among groups, which is mainly due to the earlier industrialization in history. In 2018, SHSN had the highest TCO₂ (623.9 × 10⁴ t), WCN was 311.9 × 10⁴ t, and NXH was 166.4 × 10⁴ t. TCO₂ per capita in SHSN reached its minimal (≈0.12 t) in 2018 among 29 years, while WCN and NXH shared the same levels (≈0.07 t). This could be attributed to the dense population and a series of low carbon policies announced in SHSN and WCN. NXH is still in the stage of high demands on economic-centered development. The primary source for TCO₂ in the YRD is fossil fuels. The TCO₂ contributed by transportation electricity usage is continually increasing, especially after 2010. This phenomenon represents that electricity can be a significant part of the YRD’s transportation sectors’ energy consumption shortly. A complex estimation model uncovers the complexity between the economy, environment, and carbon emissions in the YRD, which indicated that the decrease of TCO₂ in YRD could not be regulated solely by economic or environmental interventions. This study highlighted the urgency for socio-economic adjustments from carbonized to decarbonized structures in the YRD.

Promoting coordinated and environmentally sustainable development of the Chinese economy is one of the primary tasks at the moment, as well as one of the sustainable development goals of the United Nations. The Resource-saving and Environment-friendly Society (RES) has created a pilot promotion policy aimed at China, with the goal of supporting the sustainable development of economic production activities while preserving natural ecosystems. In this investigation, we used the global Malmquist–Luenberger index with a slack-based measure of the directional distance function to calculate the industrial green total factor productivity (IGTFP) of 105 prefecture-level cities along the Yangtze River from 2004 to 2019; IGTFP was used as a proxy for sustainable development. Then, by considering the RES construction as a quasi-natural experiment, we used propensity score matching difference-in-differences (PSM-DID) to determine the effect of RES construction on sustainable development of the Yangtze River economic belt. We also employed the mediating effect model and triple difference (DDD) model to further analyze the mechanisms underlying the heterogeneous impacts of different urban characteristics. The results revealed three key findings. (1) According to the IGTFP calculation results, RES construction can effectively promote green technological progress while inhibiting green technological efficiency. (2) After carrying out a series of robustness tests, we found that RES construction increased the IGTFP of pilot cities by 4%, indicating that RES construction can significantly promote the sustainable development of pilot cities along the Yangtze River. (3) The results of the mechanism analysis showed that RES construction had a significantly positive impact on sustainable development through technological innovation, human capital, energy conservation, and emission control. In terms of different urban characteristics, the RES construction promoted sustainable development in first-tier cities, second-tier cities, and resource-based cities. We summarized the practical experience of the RES construction as a typical pilot promotion policy. It provides an empirical basis for planning the construction of eco-friendly urban areas in the 21st century and responding to the international community’s sustainable development goals from a Chinese perspective.