Spatial-temporal characteristics and regional differences of the freight transport industry's carbon emission efficiency in China.

The freight transport industry is an important field in which to achieve the goal of carbon emission reduction within the transportation industry. Analyzing the spatial-temporal characteristics and regional differences in the freight transport industry's carbon emissions efficiency (CEE) is an essential prerequisite for developing a reasonable regional carbon abatement policy. However, few studies have conducted an in-depth analysis of the freight transport industry's CEE from the perspective of geographic space. This study combines the super-efficiency slack-based measure (SBM) model and the window analysis model to measure the freight transport industry's CEE in 31 Chinese provinces from 2008 to 2019. We then introduced a spatial autocorrelation analysis and the Theil index to analyze the spatial-temporal evolution characteristics and regional differences in the freight transport industry's CEE in China. The results show that (1) the overall level of the freight transport industry's CEE is low, with an average of 0.534, which showed a weak downward trend during the study period. This indicates that the freight industry's CEE has not improved, and there is a massive requirement for energy conservation and emission reduction. (2) From 2008 to 2019, CEE gradually shows a spatial distribution pattern of being "low in the west and high in the east," with a significant, positive spatial correlation (all passed the significance level test at P < 0.01). This indicates that the spatial diffusion and inhibition of the freight transport industry's CEE in adjacent areas cannot be ignored. (3) The overall differences in the freight transport industry's CEE show a fluctuating upward trend from 2008 to 2019. The inter-regional differences of the three regions (east, central, and west) are the main contributors of the total differences. Therefore, narrowing inter-regional gaps in CEE is one of the main ways to improve the freight transport industry's CEE.