Transport systems perform vital societal functions, but in their present state cannot be considered "sustainable". One of the most controversially discussed long-term solutions to climate change and air emission externalities is the introduction of hydrogen as an energy fuel and fuel cell vehicles. In this paper, we integrate the two debates on the sustainability of today's transport systems and on the opportunities, threats and possible transition paths towards a "hydrogen economy" in road transport. We focus our analysis on developed countries as well as the specific needs of the fast growing markets for car travel in the emerging economies. We conclude that the use of hydrogen can significantly reduce CO2 emissions of the transport sector, even if taking into account tailpipe and upstream emissions as well as alternative technology developments. Moreover, local air pollutants can be reduced up to 80%. Possible negative impacts, including accident risks, nuclear waste or increased biomass demand, need to be benchmarked against these benefits. Thus, we highlight the need for integrated energy and transport policies and argue for more reflexive and inclusive societal debate about the impacts and beneficiaries of hydrogen transport technologies. (C) 2008 Elsevier Ltd. All rights reserved.