The transport sector (1996) is responsible for over 25 per cent of world primary energy use and 22 per cent of CO2 emissions from fossil fuel use. It forms the most rapidly growing sector with energy use in 1996 at about 70 EJ (EJ=exajoule. Joule is a measure of energy [kg m2 s-2] and exa is 1018). Without action, this figure will double to 140 EJ in 2025. Industrialized countries will contribute the majority of this figure until 2025. After that date, the majority of transport related emissions will come from those countries that are currently developing rapidly or that have economies in transition. Transport activity increases with rising economic activity, disposable income, access to motorized transport, and falling real vehicle and fuel costs. All these determinants of travel have been favourable over the last twenty years, hence the huge increase in travel, particularly by road and more recently by air.