HU Sheng, WANG Zhenhua, XING Hanfa, LIU Wenkai, LIU Yefei, LI Jiaju, ZHANG Guanheng
[Objectives] China's transport sector is one of the fastest-growing sources of carbon emissions, with Road Traffic Carbon Emissions (RTCE) accounting for a large share. The way an urban road network is laid out may strongly influence RTCE, yet existing studies often ignore spatial non-stationarity and nonlinear effects. [Methods] This article takes 302 urban functional areas in China as the research object. Experiment data include 2019 urban road network data, road traffic carbon emission grid data, and population and GDP grid data. Firstly, ArcGIS and osmnx packages were used to visualize the road traffic carbon emissions, road grade distribution, traffic network density, and traffic network structure indicators of the 302 urban functional areas. The distribution characteristics of urban RTCE and urban road network were also analyzed. Then, the fitting effects of OLS, GWR, and MGWR models were compared and analyzed to identify the best model for relating road-network form to RTCE. Finally, based on the Multi-scale Geographically Weighted Regression model (MGWR) and SHAP analysis, the impact mechanism of road network morphology on RTCE was explored. [Results] ① The spatial distribution of Road Traffic Carbon Emissions (RTCE) exhibits a multi-center pattern, with core areas such as the Beijing-Tianjin-Hebei region (1 003.604 t/km2), the Yangtze River Delta (849.074 t/km2), the Pearl River Delta (1 615.291 t/km2), and provincial capital cities (1 168.886 t/km2), gradually decreasing toward the surrounding areas. The RTCE levels in the eastern region are generally higher than those in the central and western regions. In terms of the spatial distribution characteristics of road network morphology, the density of the traffic network and road hierarchy distribution resemble the RTCE distribution pattern. The southern regions exhibit higher Road Direction Richness (RDR), while the northern regions have higher road Grid Coefficients (GC). ② The impact of road network morphology on road traffic carbon emissions shows significant spatial heterogeneity. For example, Road Network Density (RND) has a more pronounced impact in the Pearl River Delta (0.636), while Road Direction Richness (RDR) has a greater influence in the Yangtze River Delta (0.259). Additionally, different road network morphological indicators vary considerably in their impact on RTCE across regions. ③ Road network morphology exhibits spatial non-stationarity and nonlinear effects on RTCE. For instance, the bandwidth of RND is only 45, whereas that of RCR is 215, indicating that different morphological characteristics affect RTCE at different spatial scales. In the SHAP analysis based on machine learning, which accounts for nonlinear impacts, RND is identified as the most important feature influencing road traffic carbon emissions. [Conclusions] This study employs the MGWR model and SHAP method to reveal the spatial non-stationarity and nonlinear influence mechanisms of road network morphology on road traffic carbon emissions. The results indicate that the impact of road network characteristics on traffic carbon emissions varies significantly across different regions. These differences are reflected not only in spatial distribution but also in the underlying mechanisms of influence. Therefore, when formulating low-carbon road network planning strategies, it is essential to fully consider the spatial heterogeneity, non-stationarity, and nonlinear characteristics of the road network. A comprehensive analysis from the multidimensional perspective of "density-hierarchy-structure" is recommended to promote low-carbon urban transportation. These findings provide a scientific basis for urban transportation planning and low-carbon development, contributing to sustainable urban development, improved traffic efficiency, and enhanced quality of life for residents.