Steven Holl

To Antony Wood's mind, the future of cities is vertical, replete with super-tall buildings, rooftop parks and, yes, lots of skybridges.

Antony Wood has a Blade Runner-like vision of our urban future, with zigzag skybridges linking super-tall buildings and vast green parks dozens of stories above the ground. Yet, as architects and developers link all sorts of towers in Asian and Western cities, it's starting to sound less like science fiction than 21st century reality.

“When I started this, people thought I was crazy,” says Wood, who studied skybridges in his 2003 dissertation and is now the director of the Chicago-based Council on Tall Buildings and Urban Habitat.

Around the world, some 190,000 people are moving to cities every day, or more than five and a half million people each month. By 2050, some 70 percent of humanity will live in an urban setting, according to a recent United Nations white paper that sees a need for 10,000 new cities to house three billion new urban inhabitants.

“We've got to recognize that we inhabit a different world now,” says Wood, who's also an architecture professor at the Illinois Institute of Technology. “The scale of the problem ahead of us is far greater than the problems we've already faced. If we accept that cities are going to get denser, and thus more vertical, we need to rethink our cities.”

For Wood, that rethinking begins with a broader conception of the ground level, where social interaction takes place and communities are built. Way up above, skyscrapers are primarily office, residential and hotel space.

“That's not a city,” says Wood. “If we're going to make tall buildings socially inclusive, the only way we're going to do that is to connect them at height, to allow us to introduce public zones in the sky and recreate the ground layer.”

The idea is not new. In the 1940s, the French-Swiss architect and urban planner Le Corbusier proposed building bridges and public spaces at height. But his skybridges were built at one or two stories, in Brutalist concrete European highrises after WWII, and the concept soon fell out of favor.

Wood envisions a series of bridges at 30, 50, even 100 stories, improving access and circulation as part of a network of towers. A school on the 57th floor of a building, for instance, would work only if it linked to family residences, a playground, a library.

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“If this sounds farfetched, we only need to look at Hong Kong,” says Wood.

In 1965, the developer HongKong Land built an enclosed, air-conditioned bridge over Chater Road to connect the shopping center at the base of its Prince's Building to guests at its new Mandarin Oriental Hotel. The move proved a commercial success, and HongKong Land soon expanded the concept to its other buildings across central Hong Kong.

A foot bridge in Hong Kong. Photo credit: Bobby Yip/Reuters

Other developers followed suit, and within a couple decades the Hong Kong government unofficially adopted the skybridge network as a planning tool. Today, skybridge-linked HongKong Land buildings connect nearly half a million square meters of office and retail space and encompass a population of over 20,000 workers. “You can walk several miles through central Hong Kong without touching the ground, in shopping centers, office towers, hotels,” says Wood.

A more recent example is Singapore's Pinnacle@Duxton, a seven tower, 50-story public housing complex designed by ARC Studio Architecture + Urbanism and completed in December 2009. Skybridges at the 26th and 50th stories link all seven towers and 1,848 apartments.

The 26th story bridge is for residents only and has a recreation center, jogging track, outdoor gym, children's playground and two viewing decks. The 50th story skybridge is open to the public and offers panoramic views of the city. Both hold up to 1,000 people at a time.

The Marina Bay Sands. Photo credit: Timothy Hursely (left); Safdie Architects (right)

A couple miles way, the Marina Bay Sands is said to be the world's most expensive hotel, costing a reported £4 billion. Designed by Moshe Safdie and completed in mid-2010, the hotel's three 55-story towers are topped by a rooftop SkyPark, which includes an infinity pool that seems to stretch on forever, sundecks, palm trees, gardens and a restaurant. At 340 meters, the SkyPark is longer than the Eiffel Tower is tall.

Linked Hybrid, a Beijing housing complex completed in 2009, has the look of a Philip K. Dick fever dream. Set amid vast reflecting pools, this 220,000 square-meter, eight-tower compound uses translucent glass bridges to connect 700 apartments, a hotel, shopping areas, a multiplex, a kindergarten and underground parking.

Steven Holl Partners designed it as “an open city within a city.” The Council on Tall Buildings chose it as its best tall building overall for 2009, arguing that the project embodies "where the future of tall buildings and urban cities is heading.”

That future has begun to appear in the West as well. The Telekom Center is a six-tower, skybridge-linked office complex on the outskirts of Munich, completed in 2004. Skyways and catwalks connect downtown buildings in Minneapolis, Atlanta, Calgary and other North American cities. And of the seven finalist proposals for the new World Trade Center in downtown New York City, five incorporated skybridges.

The design ultimately chosen did not, speaking to the real challenges that skybridges present. Since 9/11, tall buildings are seen as terrorist targets. Security, generally handled at a ground floor main entrance, becomes problematic when people are entering your building at several points, such as in central Hong Kong. The engineering is also difficult because skyscrapers need to be free to move slightly at the top. The skybridge connecting Kuala Lumpur's Petronas Towers at the 41st and 42nd floors, for instance, is not anchored to the buildings but rather designed to slide in and out and allow the towers to sway several feet in high winds.

Wood counters that skybridges “are the way to make our vertical cities more sustainable.” Networks of tall buildings have the potential to reduce our total energy consumption by sharing power and facilities between buildings and creating green corridors in the sky.

"This is not about sticking a few bridges in the sky," Wood says. "This is about building a three-dimensional city, where these zones in the sky become the responsibility of the city."

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