Henry Grabar is a staff writer for Slate’s Moneybox and a former fellow at CityLab. He lives in New York.
Meet the new bridge, same as the old bridge.
Back in the mid- to late-1990s, Columbus, Ohio, faced a familiar urban problem. The city’s vibrant High Street was split by the trench of Interstate 670, separating the hip Short North area from the Convention Center and downtown. For years, American cities like Boston, Phoenix, Seattle, Washington D.C., and Dallas have been hiding urban highways beneath decks, caps or lids supporting parkland. But Columbus tried something new: it hired architect David Meleca to transform the drab overpass into what by all accounts was America’s first habitable bridge, modeled after Florence's Ponte Vecchio, which debuted in 2004. Despite the fact that eight lanes of traffic run below and around it, the new block of High Street, lined with shops and restaurants, has proved largely indistinguishable from those around it.
The habitable bridge, out of favor since the Renaissance, has been making a bit of a comeback. After the I-670 cap opened in Columbus, Iraqi-British architect Zaha Hadid designed this stunning habitable bridge in Zaragoza, Spain, completed in 2008 (pictured above). The following year, architect Steven Holl, whose designs often include sky-borne passages, completed an apartment complex in Beijing where a swimming pool, bookstore and cafe hang between buildings. Plans are underway for habitable bridges over highways in Washington, D.C., and New Haven, Connecticut, and architects and planners have proposed similar ideas in Montreal, Abu Dhabi, Amsterdam, Acapulco, and London.
It's hard to imagine, but habitable bridges were once the rule rather than the exception. At one time, nearly every city in Europe could boast at least one chaotic span that balanced people, shops and houses over a river. The most famous was probably the old London Bridge, which Mark Twain portrayed in delightful detail in The Prince and the Pauper:
The Bridge was a sort of town to itself; it had its inn, its beer-houses, its bakeries, its haberdasheries, its food markets, its manufacturing industries, and even its church.... Children were born on the Bridge, were reared there, grew to old age, and finally died without ever having set a foot upon any part of the world but London Bridge alone…
Gradually, habitable bridges were replaced by their familiar single-use counterparts. Installing the urban infrastructure of modern life—plumbing, for instance—on solid stone bridges was nearly impossible. The design suffered further with the completion of Paris’ spare and uninhabitable Pont Neuf in the late 16th century, which attracted admirers from all over Europe.
"From the Renaissance on," says Alan Plattus, a professor of urban design at the Yale Architecture School, "there’s a developing idea that a bridge is a place where you get outside the city, where you get a view of the city." After the Pont Neuf, habitable bridges that burnt down were not rebuilt, and new bridges tended to be, well, just bridges. When Columbus started its freeway cap project in the early 2000s, there were only four habitable bridges left, in Florence (the Ponte Vecchio, at left), Venice, Bath, and Erfurt, Germany.
In Columbus, obscuring the view was the goal—the I-670 is no Seine—but Meleca found, like generations of European planners before him, that suspending an entire street poses a series of infrastructure challenges. Because bridges do not have the natural insulation of solid ground, simple concerns like heating pipes required inventive solutions. Forging a reliable connection between the roadway, which should give a few inches when trucks roll over the bridge, and the buildings, which should not, was another test. According to Meleca, these innovations go mostly unremarked, which is fine with him. "That’s when you know you’ve succeeded," he says. "When they don’t know they’ve gone over a bridge."
Unlike most single-use spans and green freeway decks (which can indirectly increase nearby property values), the I-670 cap and its kin are designed to be profitable investments. In Columbus, developer Jack Lucks, chairman of Continental Real Estate Cos., spent about $7.5 million on the buildings, while the city and state paid just $1.9 million for the bridge. If other cities replicate the Columbus model, the habitable bridge could shift the task of mending the urban fabric toward the private sector.
That's what's happening in New Haven, which has undertaken an enormous project to mend the scar of another urban renewal highway, using a similar public-private financing model. In order to turn the College Street overpass into a connecting street alongside a new biotech facility, the city is combining traditional government funding for infrastructure with the management and investment of a Massachusetts developer to build—and rent—the lab at 100 College Street. Within the next 10 years, New Haven should have a "habitable bridge" of sorts in College Street, at least on the west side, where traffic will roll under the new building.
In Washington, D.C., there are two projects in the works to build habitable bridges over Interstate 395. Plans to redevelop the District’s sleepy Southwest quadrant show the 10th Street overpass expanded into a tree-lined street with buildings on each side suspended above the highway. Closer to downtown, development group PGP is attempting to build an entire business district above Interstate 395.
Top image: Flickr user Wojtek Gurak.
Columbus photos: Flickr user Great Photographicon.
Left inset : Flickr user Colby Blais Dell.