This paper focuses on urban passenger transport eco-efficiency, which can be defined as the production of maximum benefits to society while minimising environmental impacts from urban transport’s inputs of energy and materials. Researchers have intensively studied transport’s varied environmental impacts, particularly through Life Cycle Assessment; this paper argues that primary transport energy per capita is presently the best measure of impact. Although transport’s societal benefits have generally been regarded as self-evident, access to out-of-home activities, not passenger-km, should be considered as the fundamental useful output of an urban transport system, since transport is a derived demand. We argue that access levels are roughly similar in all high-income OECD cities, so that these cities can be ranked on transport eco-efficiency simply on the basis of per capita primary transport energy.