Once an elevated freight railroad that ferried goods and materials to and from Manhattan's west side factories, now a public park featuring sun decks, ponds, and native plantings, the High Line is not your typical piece of infrastructure. Built in the early 1930s to move train traffic off 10th Avenue, the viaduct once stretched more than two miles from the west side rail yards to St. John's Park Terminal on Spring Street. Unlike most elevated tracks, which run above the street, the High Line cut through the center of the block and into the warehouses it was meant to serve, creating a safer environment at grade. Though an immensely functional artery, use of the route declined with the rise of commercial trucking in the 1950s. In the 1960s the city demolished the southern section from Gansevoort Street down to Spring Street, and the last train traveled the track in 1980, pulling a load of frozen turkeys.

The High Line was abandoned. Over the next 25 years, nature was left to its own devices and allowed to take its course. Among the steel rails and crushed rock grew trees, grasses, and wildflowers. What once was a bustling corridor of commerce became a bewitching garden in the city, an enchanted ruin open only to the adventurous.

The elevated track would have stayed that way until it eventually was demolished if it hadn't been for the efforts of two men, Joshua David and Robert Hammond, who in 1999 formed Friends of the High Line and began advocating for its preservation and adaptation into a public space. David, a journalist, had lived in the shadow of the rail for years, but didn't know its full extent until doing research on West Chelsea for an article. “When I realized it was still intact from Gansevoort to 34th [streets] I thought, what an amazing opportunity, what a way to experience the city, it's so unique and special,” he says.

Friends of the High Line obtained the support of Mayor Michael Bloomberg, raised more than $130 million, and held an international design competition that attracted 720 entries from 32 countries. In 2004, a team was selected that included landscape design firm James Corner Field Operations; architects Diller Scofidio + Renfro; and lighting designers L'Observatoire International.

URBAN INFRASTRUCTURE / URBAN LANDSCAPE “The question for our team was how to take this incredible landscape and bring people up onto it without destroying it,” says Ric Scofidio of Diller Scofidio + Renfro. “How do you put a path on it while keeping the serene quality?”

The designers did not want to follow in the footsteps of the project's predecessor, the Promenade Plantée in Paris—another park built on an abandoned railroad viaduct—which functions more as a thoroughfare than as a place to relax and enjoy the surrounds. The team's answer was to develop a concrete planking system whose long tapering members vanish into the plantings, creating an integrated trail and a sense of walking through the growth rather than down a “linear path through a garden,” as Lisa Switkin, associate principal of James Corner Field Operations, puts it. The system is raised to accommodate drainage and electrical systems, and integrates well with the existing rails. The designers also “peeled up” certain planks to form benches, creating a seamless flow from path to seating. To further slow down the traffic and create a leisurely environment the team developed “pooling” areas to catch visitors, such as a terraced seating area perfect for viewing the city, and a grassy lawn just right for a nap.

But before construction could begin, the slate, so to speak, had to be wiped clean. The existing rail bed, and in some places the concrete decking, had to be removed, and the tracks were tagged so they could be returned to their original locations. While the existing steel structure was quite robust, some of it had to be repaired or replaced, and the entire expanse had to be sandblasted in containment units and then primed and repainted. Steel beams also were removed to allow for access stairs at various entry and exit points along the line.

LANDSCAPE / PLANTINGS The vegetation that had grown on the High Line during its years of dereliction was a vigorous mix of native and invasive species that needed no help from green thumbs to grow. This meadow in the sky also gave a surreal quality to the postindustrial surroundings. The designers wanted to maintain both of these qualities when developing and integrating a manmade landscape. “From the beginning one of the primary challenges was to keep the spirit of what was already a magical space,” Switkin explains.

The designers put together approximately 210 species of mostly native grasses and perennials, a collection that built off the self-sown greenery and its resilience. They also worked with the microclimates that exist along the 1.45-mile course, which switches from open to sheltered, wet to dry, sun to shade, and woodland to grassland. The plants chosen are wild in character, distinct from the look of a traditionally cultivated garden where the interventions of the horticulturist are clearly visible. This varied texture is further enhanced by the fact that the plants' bloom cycles were staggered to maintain a changing but constant variety of color throughout most of the year.

Another factor that guided the selection of plants is the High Line's lack of depth—it is basically a 6-acre green roof. “It's quite different from most park landscapes in the city because the shallow rooting zones generally only have between 18 to 24 inches of soil,” Switkin says. The team combined a highly engineered soil mix that accounts for this minimal depth with a 2-inch layer of crushed stone, reminiscent of railroad ballast, which encourages water retention.