The development of traffic infrastructure involves massive land use changes along the transportation routes and stimulates urban sprawl at transfer nodes, leading to a degradation in ecosystem services, including soil conservation. For developing countries, especially for China, it is very important to differentiate the influences between different standards of traffic infrastructure associated with the different administrative levels of the regions where they are constructed on soil conservation. In this study, we attempt to analyze the differences in the influence of accessibility at different levels on soil conservation, for the case study area in Hunan province in China. The results indicate that: (1) traffic conditions in Hunan province have witnessed continuous improvement, and the time taken to access mega-cities, prefecture-level cities, and county-level cities from various regions has been significantly reduced. (2) The total annual soil conservation in Hunan province is maintained at approximately 2.93 × 10⁹ t. However, the spatial heterogeneity shows severe degradation in regions with lower accessibility, and weak enhancement in regions with higher accessibility. (3) A negative spatial autocorrelationship exists between accessibility and soil conservation at all levels, with the increase of administrative rank of the destination making it more obvious and intense, along with an increased tendency for the spatial distribution to concentrate. (4) Building more railways and highways from prefecture-level cities with LH clusters nearby as transfer nodes, instead of the construction of national roads and provincial roads that diverge from these railways and highways, will help limit the massive expansion of construction land and soil erosion within prefecture-level cities, rather than spreading to towns of LH clusters. This research provides an important scientific basis for future regional planning and traffic infrastructure construction, and also a reference for traffic infrastructure development in other geographically similar regions on a synchronous development stage in the world.

Megacities represent an advanced stage of urban development where expansion-induced carbon debt increases environmental pressure. This study examined the spatial response of carbon stock change to urban expansion in megacities. Based on 2000–2020 land use/land cover data for 11 Chinese megacities, concentric ring analysis and spatial exploratory methods were employed to quantify urban expansion intensity and carbon stock change and to infer stage transition characteristics. The results indicate that: (1) urban expansion intensity declined over time as growth shifted from rapid edge or infill expansion toward smart-growth-oriented development; (2) carbon budget fluctuations weakened, and emission patterns evolved toward improved carbon balances and enhanced sink effects, with Beijing and Tianjin emerging as local carbon sinks; (3) the carbon effects of LUCC showed a stage transition from rapid expansion–intensive emission to slow expansion–moderate emission, and policy intervention reshaped this relationship. The carbon effects of megacity expansion are stage-dependent rather than linear, and policy intervention can shift this relationship before economic maturity, offering guidance for low-carbon planning in developing-country contexts.