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The Relationship Between Subways and Urban Growth

Key takeaways from a new study on the effects of subway location and expansion around the world.
Tokyo is the largest city in the world, but ranks fifth in terms of its number of subway stations.
Tokyo is the largest city in the world, but ranks fifth in terms of its number of subway stations.REUTERS/Kimimasa Mayama KM/CCK

In the major cities of the world, subway systems are typically seen as a means to foster density, reduce reliance on cars, mitigate sprawl, and provide residents with access to affordable transportation. Recently, subways have also been seen as contributors to gentrification, as the advantaged and affluent colonize locations near stations to reduce their commutes and save time. But how do subways really affect urban development? To what degree do they promote density and centralization?

A new study by my University of Toronto colleague Marco Gonzalez-Navarro and Matthew A. Turner of Brown University helps to flesh out this relationship by looking at the effect of subway location and expansion on transit ridership, population growth, and the development of urban areas. To get at this, the authors developed a unique data set describing all subway systems in the world. Their data includes information on underground, surface, and above-ground rail transit lines, and identifies the latitude, longitude, and date of opening for every station. To examine the effect of subways on urban development, they utilize data from satellite images of the world at night (drawn from NASA satellites), and then calculate “light intensity gradients” for each city to measure its centralization. Finally, they draw upon data for population changes from the United Nations.