In the context of intensified global climate change, accurately calculating the carbon emission reduction costs in the transportation sector is of significant practical importance for scientifically advancing carbon reduction efforts and achieving carbon peak and carbon neutrality goals. This paper employs the directional distance function (DDF) to assess the shadow prices of carbon dioxide emissions in the transportation sector across various provinces in China from 2010 to 2020. The results indicate substantial disparities in carbon reduction costs among provinces, with an overall trend of “higher costs in the west and lower costs in the east,” placing greater pressure on the western regions. Requiring all regions to achieve the same reduction targets may lead to inequitable outcomes. Based on these findings, this paper suggests formulating more targeted, differentiated carbon reduction policies to promote a green transition in the transportation sector that balances efficiency and equity.