What’s more, the way streets are laid out now determines the pattern of later growth. “Street connectivity fundamentally constrains both people’s travel choices and also how cities can adapt and evolve in the future,” says Millard-Ball.
Throughout much of the 20th century, urban growth in North America and Europe emphasized car-led development. Cul-de-sacs were perceived as family-friendly and safer for children, but contributed to car-dependency and other problems associated with sprawl.
Today, at least in higher-income countries, more cities are moving away from disconnected street networks and are adopting policies that encourage walkability and transit-oriented development. A ‘hipsturbia’ trend sees developers catering to the millennials by building neighborhoods with easy walking access to cafes, restaurants and local shops.
That isn’t the case in lower and middle-income countries, where most of the world’s population growth is taking place, much of it on the periphery of cities. One billion people are currently thought to be living in slums that typically grow up without government planning or oversight.
Middle classes are also drawn to the edges of these cities to escape soaring real estate prices in the urban core. These new developments are often built by private interests with little consideration for environmental impact or social equity.
“As the middle class swells in many of these countries with income growth, those preferences for having a larger home is leading to this move to the periphery,” says Anjali Mahendra, the Director of Research at the World Resource Institute’s Ross Center for Sustainable Cities. “Private developers are coming in to cater to that demand.”
Gated communities, an extreme example of a disconnected neighborhood, are flourishing in response to fears about urban crime. In South Africa, walled-off estates that originally were reserved for whites during apartheid have since evolved into exclusive properties for the well-off. High-end gated estates represent 15 percent of the value of the country’s entire property market, but only 5 percent of the number of residential properties, according to a 2016 analysis by Lightstone Property, a local real estate valuation firm.
Sometimes, governments are the ones who spearhead sprawl. In 2001, Mexico embarked on an ambitious $100 billion project to build affordable housing across the country. But many of the new developments were built far away from city centers and job opportunities, and featured long blocks of houses clearly designed around car ownership. In some cases, the government failed to bring in public infrastructure, so new residents didn’t have access to tap water, a stable electricity supply, or transit. Some of the new neighborhoods began decaying, and hundreds of thousands of people have since left those homes.
“You’re seeing cities willfully put affordable housing in very disconnected locations, and that is a big problem because they’re doing it at a very large scale,” Mahendra says. “You’re going to see these inequalities increase, and the environmental impact increase.”
