Drivers of transportation CO2 emissions and their changing patterns: Empirical results from 18 countries

Transportation continues to be a significant contributor to CO2 emissions and may potentially be the final sector to reach its carbon peak in the future. Identifying the drivers of transportation CO2 emissions (TCE) and understanding their changing patterns is crucial to effectively control TCE. However, previous studies can only obtain fixed parameter values of TCE influencing factors throughout the study period, or although they can obtain the impacts of specific factors on TCE with accompanying changes over the years, they cannot conveniently clarify the changing patterns. Therefore, the key contribution of this study resides in providing a spatially explicit understanding of the heterogeneous primary drivers of TCE across countries, and in uncovering the temporal dynamics of these primary drivers' influences on TCE. The results show that at the country-group level (considering 18 selected countries as a group, collectively representing over 60% of global TCE), the drivers of TCE were GDP, energy intensity, and population in order of contribution. However, for developed countries, GDP and energy intensity contributed less to TCE than for developing countries. In addition, the influence of energy intensity on TCE declined faster than that of GDP, suggesting that decoupling TCE from economic growth should always be the top priority regardless of a country's development level. Policy-wise, for countries where GDP is the primary driver of TCE, measures to reduce transportation activities include industrial upgrading, coordinated planning, and accessibility promotion. For countries where energy intensity is the primary driver of TCE, measures to improve transportation efficiency consist of technology adoption, regulation/pricing, and habit improvement.