Introduction: the complexity of urban environments

Urban areas have been recognised for decades as complex systems (North 1990), akin to organic structures (Simon 1997). Both comparisons aptly acknowledge the dynamics and interactions at play in cities and metropolitan areas, complexities which tend to scale up with population and size. Transportation is a key component of the development and management of increasingly large and complex cities because it provides the means to move goods and people along mobility chains. Ideal urban mobility systems provide access to activities as quickly and conveniently as possible.

High quality urban transport generally requires the participation of multiple organisations across different elements of the system. While political entities define objectives to be achieved, planning agencies design the system (for example, operations, infrastructure). Different types of operators oversee vehicle operation, infrastructure, traffic management, parking, and so on. Regulating agencies establish and monitor market rules; other agencies undertake the enforcement role. The success of transportation interventions, especially the implementation of Bus Rapid Transit (BRT) services, depends on all these entities acting in concert, and this is where complexity is born. Lack of consistency between these entities will inevitably lead the system to underperformance or even to collapse. Each time a new economic agent (or actor) enters the system, new interactions develop, either with other private agents, or with public entities, or both, and readjustments are needed. As noted by Macário (2011), in mobility systems the mutual dependence between actors requires the system to have structural consistency. It is this consistency that provides alignment between operational results and planning objectives and between these and the strategic vision of the city.

The implementation of a BRT system is always done in cities where an urban mobility system already exists, however informal. Implementation can often be disruptive to this pre-existing system, whether due to lack of intermodal adjustment, inequitable situations between new and incumbent operators, and conflicts over tariffs, or to gaps in information systems. Examples of such disruptions are reported in several cities, such as Bogotá, Santiago, Léon and Mexico City (Flores and Zegras 2012; Kash and Hidalgo 2012) and are also addressed in Chapter Four of this book.