by Shlomo Angel and Alejandro M. Blei

Abstract: Urban transport and land use policy are informed by our perceptions of the prevailing spatial structure of cities. This structure can be characterized by five models: The Maximum Disorder model, The Mosaic of Live-Work Communities model, the Monocentric City model, the Polycentric City model, and the Constrained Dispersal model, where the great majority of jobs are dispersed throughout the metropolitan area and where workers and workplaces in a metropolitan-wide labor market adjust their locations to be within an tolerable commute range of each other. We examine evidence from a stratified sample of 40 U.S. cities and from the 50 largest U.S. cities to show that the latter model best explains the spatial structure of contemporary American cities. The Constrained Dispersal model is, in essence, a hybrid model that combines elements of all other models. It postulates that the Maximum Disorder model is largely correct, except that it applies only to 3 out of 4 jobs but not to all jobs, and except that commuters and workplaces move to be within a tolerable commute distance of each other. It postulates that the Mosaic of Live-Work Communities model is also correct, except that it only applies to 1 out of 12 people, on average, who live and work in the same community. It postulates that the Monocentric City model is also correct, except that only 1 out of 9 jobs, on average—rather than all jobs—still locate at the CBD. And it postulates that the Polycentric City model is also correct, except that only 1 out of 4 jobs, on average—rather than to all jobs—locate in the CBD or in employment sub-centers. In essence, the great majority of workplaces is now dispersed outside CBDs, employment sub-centers or live-work communities, and is beyond walking or biking distance. Maintaining and increasing the productivity of American cities requires a sustained focus on meeting the travel demands of the great majority of commuters rather than on improving mobility at large or on transportation strategies focused on CBDs, employment sub-centers, or live-work communities.

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by Shlomo Angel and Alejandro M. Blei

Abstract: The greatest productive advantage of modern-day American cities is that they form large and integrated metropolitan labor markets. We present new evidence on the importance of self-adjusting commuting and location patterns in sustaining the productive advantages of larger metropolitan labor markets, mitigating the difficulties in coping with their sheer size, and reducing the added burdens on their transportation infrastructure. As a result of these adjustments, the metropolitan labor market—defined as the actual number of jobs in the metropolitan area reached in less than a 1-hour commute—almost doubles in size when the workforce in a U.S. city doubles. More particularly, when U.S. metropolitan areas double in population, commute time should be expected to increase by a factor equal to the square root of 2. Instead, it only increases by one-sixth of that factor because of three types of adjustments that take place as cities grow in population: increases in residential density, locational adjustments of residences and workplaces to be within a tolerable commute range of each other, and increases in commuting speeds brought about by shifts to faster roads and transit systems. The policy implications of these findings are that the more integrated metropolitan labor markets are, the more productive they are. We should therefore support policies that increase overall regional connectivity; policies that allow for speedier rather than slower commuting, for more rather than less commuting, and for longer rather shorter commuting to take advantage of metropolitan-wide economic opportunities; and policies that remove impediments to the locational mobility of residences and workplaces for all income groups so that they can easily relocate to be within tolerable commute range of each other.

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Abstract: Using a novel methodology, we study the changes in the population densities of the built-up areas of Manhattan and its neighborhoods from 1800 to 2010. Built-up areas were determined from historical maps, insurance maps, and air photographs, while population data were collected for census wards from 1790 to 1910 and for census tracts thereafter. We found that densities remained stable, at 200 persons per hectare, until 1840 when the growth in the built-up area could no longer keep up with rapid population growth. By 1910, average densities in Manhattan were triple those of 1840, while average densities in some neighborhoods were twice as high and more. Densities then started to decline, largely due to three public actions: the annexation of Brooklyn, Queens, the Bronx and Richmond County to Manhattan in 1898; the creation of vast new areas for urban expansion in the 1900 Topographical Bureau plan; and the building of the subway system from 1904 onwards. These actions led to the rapid decongestion of Manhattan’s overcrowded neighborhoods, as lower-income workers suburbanized while still commuting to Manhattan on a nickel fare. Densities in Manhattan declined until 1980 and have risen slightly since. New York City is now expecting a significant increase in population, entailing significant densification in Manhattan and elsewhere. Using the lessons learned from our study, we outline a densification program that could accommodate a larger population without recourse to heavy-handed land assembly for large and heavily subsidized housing projects. Our strategy is based on our conviction that we can achieve a more efficient, more equitable, and more sustainable densification in New York City with small actions on the part of the many than with big actions on the part of the few.

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