Transport in Mega-cities -- Does city size matter?

I just returned from São Paulo, perhaps the third biggest metropolitan area in the world with a population of 18 million and an endless vista of apartment towers and commercial buildings in almost any direction from the center.  The traffic problems are large and reported in the daily newspapers as the peak number of kilometers of the main road network in congested conditions (equivalent to LOS F).  This indicator tends to range between 100 and 200 km for any given day.  The resources that mega-cities have at their disposal are also unusually large, but one may wonder—are there are economies or diseconomies of scale with city size?

The answer is probably both: yes and no, depending on the factor and conditions.  Complexity usually increases non-linearly in network problems, so it is logical to think that the problems of traffic management and public transport integration are disproportionately more difficult in mega-cities.  But anecdotal evidence also suggests that larger cities have significant comparative advantages—otherwise they would stop growing or simply shrink. As the 2009 World Development Report describes, there are limits to growth of cities and competitive factors involved in agglomerations.

What to do then in urban transport in mega-cities?  The strategy the World Bank has taken in Latin American cities is characterized by four pillars (for more, see the World Bank Working Paper 1633: Essentials for sustainable urban transport in Brazil's large metropolitan areas, by Rebelo, 1996):

• continuous and integrated transport, land use and environmental planning,
• metropolitan coordination and priority setting,
• financial mechanisms to at least cover long-run variable costs, and
  progressive private sector participation. 
   

Working simultaneously with these four policy dimensions, along with basic investments in infrastructure and services has resulted in some progress in cities like São Paulo, Rio de Janeiro, Santiago, Bogotá, and others.  But more needs to be done, and this is what we’re working on.  Comments are most welcome.