“Low Carbon City-Green Transportation” Policy Synergy and Pollution Reduction and Carbon Emission Reduction—Based on DID Model

This study employs a multi-period DID model based on Chinese urban panel data from 2006 to 2022. It innovatively constructs a theoretical analytical framework for the “local-global” environmental regulation policy combination between urban development units and overall development, exploring the synergistic pollution reduction and carbon emission reduction effects of LCCPP and the NEVPAS. This framework reveals the “theoretical black box” of how policy combinations influence urban green development. The results indicate that, first, compared to control cities, pollution emissions and carbon emissions in “dual pilot” cities decreased by an average of 2.86% and 4.89%, respectively, and the synergistic effects of the “dual pilot” policy were better than those of the “single pilot” policy. Second, the positive impact of the “dual pilot” policy on pollution reduction and carbon emission reduction is more pronounced in eastern regions, non-resource-based cities, and areas with high environmental regulation intensity. Third, mechanism tests show that the “dual pilot” policy can positively influence pollution reduction and carbon emission reduction through three mechanisms: energy conservation and emission reduction, innovation induction, and economic agglomeration. Additionally, the “dual pilot” policy exhibits significant spatial spillover effects, not only effectively reducing local pollution and carbon emissions but also exerting a notable inhibitory effect on neighboring areas. Further research reveals that when the “dual pilot” policy exerts its pollution reduction and carbon emission reduction effects, it can enhance regional green output levels, strengthen property rights protection, and effectively promote regional green high-quality transformation without sacrificing economic growth.