The transportation sector is a major source of greenhouse gases and air pollutants, and it has a crucial effect on the synergistic reduction of NO_x and carbon. In order to find the energy-efficient vehicle technologies with the highest net reduction potential and lowest net reduction cost over the life cycle, this study traced the CO₂ and NO_x emission streams of 33 energy-efficient technologies, hidden in the supply chain during the production phase, through structural path analysis, and measured the emission reductions during the use phase using the emission factor method. Moreover, we applied structural decomposition analysis to quantify the three main drivers, including emission intensity, industrial structure, and final demand, of changes in CO₂ and NO_x emissions from 11 transport subsectors during 2012–2018. Results indicate that CO₂ emissions of the transport sector more than doubled from 2012 to 2018; however, the influence of NO_x was less significant. The final demand of the road subsector was the most significant driver contributing to CO₂ emission changes, with an increase of 109.27 Mt. The emission intensity of road transportation caused the greatest mitigation effect on NO_x emission changes, with a decrease of 1902 Kt. The findings of the scenario analysis demonstrate that the most efficient action of the pure electric technology for passenger cars reduces 20.92 Mt NO_x emissions, and the parallel hybrid technology for heavy trucks offers the greatest cost effectiveness with a net abatement of 2577 Mt CO₂ over its life cycle. Consequently, the aggressive development of new energy technology has become a prerequisite strategy to synergistically reduce CO₂ and NO_x emissions.