How we live is indicative of who we are, and both are changing. As city planners look to the next quarter century, they must factor in three profound shifts in modern society: information technology, mobility and climate.
As with everything else, technology is changing not just how we live and work, but the cities where we live and work. That technology has already affected social change, making younger generations more mobile and urban. Technology has also offered new solutions to some of the biggest challenges for 21st century urban planners—climate change and how we make our neighborhoods as green as possible.
As we look ahead 25 years and try to picture what our urban landscapes will look like, one thing is certain, the imprint of more violent storms, hotter summers and colder winters will be evident high on our rooftops and down on our streets.
The U.S. economy is becoming ever more urban, due to shifting demographics. People are living longer, which means that the percentage of households with school-age children is declining. In some cities it is under 20 percent. Younger workers wait longer to start families and older empty nesters want the easy amenities offered by city life.
That is reversing the trend of the last 50 years, when Americans sought McMansions out in the so-called exurbs to raise their families. Now, even if they're not in a city center, people want to be able to work from, or at least near, their homes.
"That means an adjustment in what that housing stock looks like," said Harriet Tregoning, who recently joined the Obama administration's Department of Housing and Urban Development as director of the office of sustainable housing and communities. "There will be fewer large family homes, more smaller units used at the beginning and end of adulthood."
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Tregoning's unique visions of transportation, parking and energy usage, while heading the District of Columbia's Office of Planning, prompted one urban blogger to deem her the city's "futurist-in-chief."
Tregoning points to the millennial generation, whose employment and wage growth has been weakest in the economic recovery. They may not have a lot of income now to be able to live where they want, but they're willing to live in a smaller space and have all the amenities of a mixed-use, mixed-income neighborhood.
"Small units are going to be in demand, and most of our communities haven't built those small units before," she said. "Yes, it's a niche, but we have no product."
As for transportation, she envisions lots of streetcars and other public transit. Some of the lanes that we're now using to park vehicles are going to be given over to pedestrians, bicyclists or transit users because people are going to be driving a lot but owning fewer cars.
"Every car that we have is going to be driven by more people, and more times a day, but we will store those vehicles less. The streets are going to look a lot different."
Not just the streets. The buildings and landscapes will, too, as cities try to adapt themselves to the growing crisis of climate change.
"Clearly cities are already starting to and will increasingly have to grapple with the adaptation that's required by climate change. That adaptation will have to account for sea level rise, more intense storms, more flooding in coastal areas and in inland areas from rivers," said Douglas Foy, CEO of Serrafix, a strategic consulting firm focused on environmental, energy, transportation and climate change issues.
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Foy, former secretary of commonwealth development in the administration of then-Massachusetts Gov. Mitt Romney, points to potential new building codes requiring that electrical and IT systems be put on higher floors. He also said urban planners will need to incorporate more green space into flood-prone cities because that will turn out to be one of the best barriers or adjustments to flooding and storm issues. He points to Boston's "Emerald Necklace," an 1,100-acre chain of parks, as being an enormously valuable flood control device, because you can flood the esplanade with the Charles River.
"It's natural features built into cityscape. They are a comparatively inexpensive way to be resilient," said Foy.
Foy and Tregoning also envision cities in which cars drive themselves, parking spaces tell you when they're vacant and restaurants grow their own food on their roofs. These cities will also have to address the so-called, "heat island effect," which is when their internal energy ends up heating themselves from within. This is why large cities are often 10 to 15 degrees hotter than their nearby suburbs.
"You're going to see lots of green roofs, greener streets, ...more street trees that provide shade," said Tregoning.
The American Society of Landscape Architects is promoting the idea of "The Edible City," in which under-utilized spaces, such as rooftops, abandoned lots, or even parking spaces, can be converted to "green" with vegetable gardens. The idea is to have residents eat healthier by having access to fresh fruits and vegetables. The society says 41 million in the past year grew vegetable gardens but much more can be done. "We want to be able to integrate agriculture into untapped urban areas," said Phillip Stamper-Halpin, a society spokesman.
What's more, whether it's white roofing to reflect the sun, shared bicycle programs or shared automobile ventures, like Zipcars, a movement has already begun, but only just begun, said Tregoning. The basic infrastructure of cities will be rebuilt over the next 25 years, and integration of technology and traditional infrastructure to make urban landscapes more energy efficient will offer endless possibilities for joint ventures between municipalities and corporate America.
As cities enlarge, urban centers will be injected into what were formerly suburbs. First ring suburbs and second ring suburbs, like Bethesda and Rockville, Md., are examples of rapidly urbanizing regions. The two, just outside the D.C. limit, are extremely popular with millennials and empty nesters. These municipalities are adding transit, shortening commutes, and putting housing near jobs. That, in turn, supports retail and service sectors.
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While Americans will still go to work in office buildings, they will do it less frequently, and their offices may not even be their own. So-called "hoteling" of office space, where no one has a permanent desk but each employee is simply assigned a desk if/when they show up, is becoming increasing popular as workers are off-site more often.
"Every time someone signs a new lease, they're taking up less office space per person," said Tregoning. "They are doing that for cost and flexibility. It is not a reflection of jobs but of a different type of space need."
And that gets back to the changing social dynamics of the millennials. Even more so than the previous cohort, they demand choices—choices about how and when they work—more flexibility and a work-life balance. They want choices in transportation. They want conveniences and amenities. But perhaps most importantly, they are keenly aware of their changing planet and will likely be more accepting of and inventive in how they accommodate and adapt to that change. More than anything else, that will change the way they live and the cities in which they live.
—By CNBC's Diana Olick. Follow her on Twitter @Diana_Olick.