This paper examines the extent to which countries have succeeded in decoupling transport emissions from economic growth, and how changes in emissions intensity, economic growth, and population growth have contributed to changes in transportation-related emissions. The paper employs a modified version of the Tapio decoupling model, and demonstrates that over the 1990–2018 study period only 12 of 145 countries achieved “absolute decoupling,” defined as reducing emissions while growing gross domestic product. The majority of the top emitters remain in a “relative decoupling” state, with emissions growing more slowly than gross domestic product. Many of the middle- and low-income countries have not achieved decoupling; their emissions are growing as fast as or faster than gross domestic product. To understand the driving factors of transport-related carbon emissions, the paper conducts index-decomposition and an econometric analysis. The results reveal that while transportation emission intensity has declined in most countries, economic growth and population growth have offset these declines. If these patterns continue, achieving the goals of the Paris Agreement with improvements in efficiency alone seems unrealistic. The paper also shows evidence that higher energy prices are associated with strong emissions reduction.