The gap between relatively developed and less developed areas in China has become more evident with economic development. However, only a few investigations have compared factors of transportation CO₂ emissions in relatively developed and less developed areas at the micro level. Factors differ for transportation CO₂ emissions between areas. To assess their differences, we select Guangdong and Guangxi provinces in China as examples. This study conducted a decoupling research between transportation CO₂ emissions and economic output based on the Logarithmic Mean Divisia Index (LMDI) decomposition and Tapio decoupling model during 2000-2017. The LMDI model successfully quantified the effects of six factors, focusing on technology-related factors, i.e., research and development (R&D) efficiency and per capita R&D expenditure. Different factors of transportation CO₂ emissions in the two provinces were then compared. Results were as follows: (1) Four decoupling states appeared in the two areas. (2) Per capita R&D expenditure was the primary contributor to increased CO₂ emissions, followed by population size. Relative to those in Guangdong, the two effects were weaker in Guangxi. (3) Energy intensity was the major inhibitor of CO₂ emissions in Guangdong, followed by R&D efficiency. The two effects can reduce CO₂ emissions in Guangxi, although the inhibitory effects were relatively small. (4) Freight transportation intensity in Guangdong increased CO₂ emissions, whereas it decreased CO₂ emissions in Guangxi due to the extremely weak inhibitory effect. Finally, the study provides valuable suggestions for the development of low-carbon transportation in different areas.