The New Suburbs: Evolving travel behavior, the built environment, and subway investment in Mexico City
Mexico City is a suburban metropolis, yet most of its suburbs would be unfamiliar to urbanists accustomed to thinking about US metropolitan regions. Mexico City’s suburbs are densely populated—not thinly settled—and its residents rely primarily on informal transit rather than privately-owned automobiles for their daily transportation. These types of dense and transitdependent suburbs have emerged as the fastest-growing form of human settlement in cities throughout Latin America, Asia, and Africa. Wealthier and at a later stage in its economic development than other developing-world metropolises, Mexico City is a compelling place to investigate the effects of rising incomes, increased car ownership, and transit investments in the dense, peripheral areas that have grown rapidly around informal transit in the past decades, and is a bellwether for cities like Dakar, Cairo, Lima, and Jakarta.
I begin this dissertation with a historical overview of the demographic, economic, and political trends that have helped shape existing urban form, transportation infrastructure, and travel behavior in Mexico City. Despite an uptick in car ownership and use, most households—both urban and suburban—continue to rely on public transportation. Furthermore, suburban Mexico City has lower rates of car ownership and use than its central areas. In subsequent chapters, I frame, pose, and investigate three interrelated questions about Mexico City’s evolving suburban landscape, the nature of households’ travel decisions, and the relationship between the built environment and travel behavior. Together, these inquiries tell a story that differs significantly from narratives about US suburbs, and provide insight into the future transportation needs and likely effects of land and transportation policy in these communities and others like them in Mexico and throughout the developing world.
First, how has the influence of the built environment on travel behavior changed as more households have moved into the suburbs and aggregate car use has increased? Using two large metropolitan household travel surveys from 1994 and 2007, I model two related-but-distinct household travel decisions: whether to drive on an average weekday, and if so, how far to drive. After controlling for income and other household attributes, I find that the influence of population and job density on whether a household undertakes any daily car trips is strong and has increased marginally over time. By contrast, high job and population densities have a much smaller influence on the total distance of weekday car travel that a household generates. For the subset of households whose members drive on a given weekday, job and population densities have no statistical effect at all. Contrary to expectations, a household’s distance from the urban center is strongly correlated with a lower probability of driving, even after controlling for income. This effect, however, appears to be diminishing over time, and when members of a household drive, they drive significantly more if they live farther from the urban center. The combination of informal transit, public buses, and the Metro has provided sufficient transit service to constrain car use in the densely populated suburban environments of Mexico City. Once suburban residents drive, however, they tend to drive a lot regardless of transit or the features of the built environment.
Second, how much are the recent trends of increased suburbanization, rising carownership, and the proliferation of massive commercially-built peripheral housing developments interrelated? To investigate this question, I first disentangle urban growth and car ownership trends by geographic area. The fastest-growing areas tend to be poorer and have had a much smaller impact on the size of the metropolitan car fleet than wealthier, more established neighborhoods in the center and western half of the metropolis. I then zoom in to examine several recent commercial housing developments. These developments, supported by publiclysubsidized mortgages, contain thousands of densely-packed, small, and modestly-priced housing units. Their residents remain highly reliant on public transportation, particularly informal transit, and the neighborhoods become less homogenous over time as homeowners convert units and parking spaces to shops and offices. Finally, I use the 2007 household travel survey to model households’ intertwined decisions of where to live and whether to own a car. As expected, wealthier and smaller households are more likely to purchase vehicles. However, they prefer to live in more central areas where households with cars tend to drive shorter distances. If housing policy and production cannot adapt to provide more centrally-located housing, growing incomes will tend to increase car ownership but concentrate more of it in areas where car-owning households drive much farther.
Third, how has the Metro’s Line B, one of the first and only suburban high-capacity transit investments, influenced local and regional travel behavior and land use? To explore this question, I compare travel behavior and land use measures at six geographic scales, including the investment’s immediate catchment area, across two time periods: six years before and seven years after the investment opened. Line B, which opened in stages in 1999 and 2000, significantly expanded Metro coverage into the densely populated and fast-growing suburban municipality of Ecatepec. While the investment sparked a significant increase in local Metro use, most of this increase came from people relying on informal transit, rather than cars. While this shift reduced transit fares and increased transit speeds for local residents, it also increased government subsidies for the Metro and had no apparent effect on road speeds. Furthermore, the Metro remains highly dependent on informal transit to provide feeder service even within Ecatepec. In terms of land use, the investment increased density around the stations but appears to have had little to no effect on downtown commercial development, where it might have been expected to have a significant influence. In short, the effects of Line B demonstrate much of the promise and problem with expanding high capacity transit service into the suburbs. Ridership is likely to be high, but so too will be the costs and subsidies, while the effects on car ownership and urban form are likely to be modest.
Individually, each chapter contributes to a specific body of transportation and planning literature drawn from the US as well as developing countries. Collectively, they point to connection between land use and transportation in Mexico City that is different from the connection in US and other rich-world cities. In particular, there is a physical disconnect between the generally suburban homes of transit users and the generally central location of high-capacity public transit. Addressing this disconnect by shifting housing production from the periphery to the center or by expanding high-capacity transit to the periphery would require significant amounts of time and public subsidy. Thus, contemporary policies to reduce car use or increase accessibility for the poor in the short and medium term would do well to focus on improving the flexible, medium-capacity informal transit around which the city’s dense and transit-dependent suburbs have grown and continue to grow.