Source: adapted from Barter, P.A. (2004) A Broad Perspective on Policy Integration for Low Emissions Urban Transport in Developing Asian Cities. Draft paper for the International workshop Policy Integration towards Sustainable Energy Use for Asian Cities: Integrating Local Air Pollution and Greenhouse Gas Emissions Concerns. Institute for Global Environmental Strategies, Kanagawa.
The transport development of cities is often taking place within a path dependency, resulting in different levels of mobility and ownership of passenger transport modes such as cars, buses, and rail transit. This implies that once a specific path has been elected, future developments are locked in along that path since it is difficult to diverge from. The level of accumulation in existing infrastructure and technology conveys inertia. Still, there is the potential for a path divergence when there is a strong economic, political, and public will to alter the existing situation towards a new paradigm judged to be more suitable. From a pre-industrial city relying on walking, three main urban transport development paths can be identified:
- (A) Automobile dependency. This development path leads to the setting of automobile-dependent cities with investments continuously made in motorization and developing a road and highway system. The first step usually involves the diffusion of non-motorized forms of transportation, particularly the bicycle. This was the case in cities in developed economies in the late 19th and early 20th centuries and in Asian cities (particularly China) in the 1970s. At this stage, a path divergence (1) is likely to take place towards the setting of public transit services. However, a path followed in several developing economies concerns motorization with the motorcycle as an intermediary form, which leads to cities saturated with motorcycles, buses, and some automobiles. As road infrastructure investment continues and with economic development, the outcome is a car-oriented city where the automobile accounts for the majority of the mobility of passengers. Such an outcome can also be achieved by cities that initially undertook transit developments but through a path divergence (3) moved towards automobile dependency through the abandonment of several transit services or the lack of further developments the cope with mobility demand. This was particularly the case for North American cities such as Los Angeles and Houston.
- (B) Transit-oriented development. This development path involves slow levels of motorization and moderate road building. Through massive investments in public transit and transit-oriented land use development strategies, this path leads to the setting of transit cities where the bulk of the population uses public transit to satisfy their mobility requirements. Such cities are however not that common because as many cities undertook development, an additional path was followed, which lead to the development of hybrid cities.
- (C) Hybrid cities. This development path is the outcome of further motorization, but the pace of road development comes faster than the pace of urban transit development. It eventually leads to a saturation of the transport system with buses and automobiles. This situation characterized many cities in developed economies in the second half of the 20th century. A possible path divergence involves rapid motorization and a move towards automobile dependency (3). Alternatively, through restrictions on the use and ownership of the automobile and the development of alternative modes of transportation, a path divergence can be achieved (2), leading to more transit-oriented forms.