In 1810, most of New York Citys 96,000 residents lived on the southern end of Manhattan. A year later, a three-man commission published what must have seemed a wildly ambitious plan for the citys expansion. Anticipating a population of 400,000 by 1860, the commissioners plan covered nearly the whole island in a now-famous rectilinear street grid, a design meant to make new construction as affordable and convenient as possible. In fact, the commissioners werent ambitious enough. By 1860, New Yorkers numbered nearly 814,000; by 1900, the citys population of 1.65 million had occupied the commissioners entire grid.
In his new book, Planet of Cities, my colleague Shlomo Angel argues that our urbanizing world needs a fresh dose of the commissioners audacity. Over the next 40 years, the United Nations expects the worlds cities to grow by roughly 2.7 billion residents, with nearly all that growth occurring in the developing world. UN projections have sub-Saharan Africa and the Indian subcontinent growing by close to 700 million urban residents each; for Latin America and Southeast Asia, the number is about 200 million each.
Ignoring this influx isnt an option. Rural families will arrive in an uncoordinated fashion, often entering slums that lack access to basic services and compounding such urban challenges as crime, lack of sanitation, contagious disease, traffic congestion, pollution, and vulnerability to natural disaster. But if governments respond by trying to contain urban expansion with greenbelts or urban growth boundaries that artificially restrict the supply of developable land, the result will be prices and rents higher than many arriving families can afford.
Angel writes that governments in the developing world, whose financial capacity is often limited, should focus on what may sound unglamorous: establishing an arterial grid of dirt roads throughout each citys future territory, much as the commissioners did in Manhattan. The grid should connect to the citys existing network of roads, of course, and it should cover an area that the city expects its future population growth to require. These arteries will one day carry public transportation and private traffic, and such infrastructure as water mains, sewers, storm drains, and telecommunications networks will follow their routes.
Angel suggests that cities space arterial roads less than a mile apart. That spacing will ensure that residents are never more than a ten-minute walk from public transportation. The arteries themselves should be 60 to 100 feet wide so that they can support not only regular traffic but also designated bus lanes, bike paths, and medians. At first, cities need only acquire the green space and rights-of-way for the arterial grid. Selected segments can then be improved as the city grows, the superblocks between the arteries are subdivided and developed, and the demand for services rises.
Angels approach is different from most urbanist schemes in not relying on government to make specific prescriptions about land use, development, and density—tasks that even the strong, well-financed governments of the West have often done poorly. His plan for urban development is essentially market-driven; the grid that the government creates merely establishes a sensible framework for future city growth. But governments can use the grid to shift building away from areas that are environmentally sensitive or susceptible to natural disasters, since proximity to arterial roads will be attractive to developers. By leading, rather than following, developers into new areas, cities can also avoid driving arterial roads through existing neighborhoods.
While twenty-first-century urbanization can offer millions a path out of poverty, it also presents major policy challenges. If cities in developing countries are to accommodate millions of new residents, they will have to do what New York did so well in the nineteenth and early twentieth centuries: make room for urban expansion. A sufficiently expansive, well-defined grid of arterial roads is a good first step.