there is a persistent difference between development trajectories spanning the extremes of highly energy intensive eg the united states to highly energy efficient eg japan the concept of path dependency discussed further below helps to explain these differences in energy use patterns among countries and regions even at comparable levels of income the first is characterized by the emergence of steam power relying on coal that helped to overcome the constraints of preindustrial energy systems including the limited availability of mechanical power lowenergy densities and the lack of ubiquitous and cheap transport systems see also landes the second energy technology transition is characterized by the displacement of the previously dominating coalbased steam technology cluster by electricity drives light and petroleumbased technologies automobiles aircraft petrochemicals this second transition is far from completed some two billion still lack access to modern energy services provided by electric appliances and enduse devices johansson et al