Even by New York standards, the High Line Promenade would be unusual: floating two stories above street level for a mile and a half. It might feature prairie grass, wetlands, or a beach, as it courses along the western edge of lower Manhattan, through a landscape of warehouses and smokestacks.
If the promenade is built, the structure will require a transformation. Today, the High Line is a rusty elevated railroad line that some local property owners want to see demolished. The tracks - last used in 1980 to deliver a load of frozen turkeys - are now sprouting lush berry vines and dainty saplings. Rotting ties and engine parts are largely concealed by chest-high vegetation.
Property owners have pushed to raze the structure since the late 1980s. But New Yorkers from US Sen. Hillary Rodham Clinton to actor Kevin Bacon have banded together to save the line and make it into a public walkway. Their nonprofit group, Friends of the High Line (FHL), is planning a fundraising campaign and has solicited proposals for the site.
The project has attracted major architectural firms, including Zaha Hadid, this year's Pritzker Prize winner. Four teams have put forward their ideas, which are on display at the Center for Architecture until Sept. 2.
The FHL has a long way to go in securing funding. The group hopes to receive federal money under the rails-to-trails program to help with expected costs of between $40 million to $65 million.
New York is not alone in trying to save some of its elevated past. An elevated line in Paris became the sunny Promenade Plantée (Planted Promenade) in 1988. A Chicago group hopes to refurbish the three- mile Bloomingdale line, which has been used as a bicycle path since trains stopped running in the early 1990s. And Philadelphia's Reading Viaduct Project aims to transform a former downtown commuter line into an elevated walkway. Outside major cities, there are similar projects in Jersey City, N.J., and the Florida Keys.
The High Line would be the first elevated line to be converted by an legal arrangement called "railbanking," which has already made ground-level trails of 4,431 miles of railway nationwide. Under the National Rail System Act of 1983, railway owners may lend, lease, or sell the rights to use former rail corridors indefinitely. Trail agencies borrow those rights and open the corridors for use as trails.
The High Line used to serve adjacent warehouses, some of whose owners would like to see it disappear. The line was built in the 1930s and was intended to transport much of the huge volume of goods shipped into New York harbor. But it was completed on the eve of the Great Depression and remained under-used until the industrial boom that came to New York after World War II. Rail traffic decreased with the growth of trucking in the 1950s. The line carried its last load in 1980.
Where some saw blight, others saw opportunity. Local residents Robert Hammond and Joshua David felt like pioneers when they founded FHL in 1999.
"When we started the organization we really didn't know how people would react to it, whether people would consider it a far-fetched idea," Mr. David says. Happily, he adds that the neighborhood, which is known for its artistic bent, was enthusiastic about the idea from the start.
Rudolph Giuliani, then New York's mayor, was not.
In 2001, Mr. Giuliani promised to demolish the line in a contract he formulated among the city; the line's owner, Consolidated Rail Corporation (CONRAIL); and property owners. FHL sued to invalidate this agreement on the grounds that the city had failed to observe a land-use review procedure mandated by the New York City charter.
A judge ruled in FHL's favor, but the city has appealed that decision. New York's current mayor, Michael Bloomberg, supports FHL.
Envisioning the High Line as a pleasant public space takes imagination. Late in 2003, FHL asked for proposals from design teams that thought themselves up to the task.
The architecture teams' designs each seek to disguise the structure's limitations. The TerraGRAM team, led by Michael Van Valkenburgh, plans a path that meanders side to side over the former track, obscuring the linearity of the supporting structure.
Another architectural firm plans to soften the same linearity by breaking the line into different ecological environments - a grove of trees, grasslands, and even a small beach.
At the same time, the plans aspire to accentuate qualities of the line that neglect has imparted - abundant wild greenery and an eerie tranquility.
The designs should be about "exploiting the majesty that's already there ... [about] appreciation for the industrial landscape and taking it for what it is," Mr. Van Valkenburgh says.