Economic development, which usually involves a transition from a rural, to an industrial and to a post-industrial society, is also linked with transitions in passenger mobility. A core aspect of this transition concerns the move from non-motorized (mainly walking) to motorized forms of transportation. The above figure represents a generic model of this transition in terms of the respective share of collective versus individual mobility and non-motorized versus motorized mobility. The initial stage of involves the development of collective forms of transportation (tramways, subways, buses) while individual forms of transportation (mainly the automobile) become prevalent at a later stage of economic development. This is particularly linked with the growth of individual incomes where at some point individual motorized mobility becomes affordable to a large share of the population. While in developed economies (e.g. North America and Western Europe) this transition took place over several decades, if not a century, many developing economies are experiencing a fast mobility transition, which is placing pressures on their transport systems. It remains to be seen how the balance between individual and collective as well as motorized and non-motorized will pan itself out in the future. It is expected that collective and non-motorized forms of mobility will play a greater role in an increasingly urbanized world where sustainability issues are more prevalent.