Almost 5 million people a year visit the High Line, a park built on an old railway, in Manhattan. (Adrian Higgins/The Washington Post)

On Manhattan’s Far West Side, they built an elevated railroad in the 1930s because freight trains and pedestrians kept colliding down on 10th Avenue. The trains won.

On the High Line today, the locomotives are long gone, and the pedestrians have emerged the victors. Seven days a week, a shifting throng simultaneously observes and forms its own pageant. By 10 a.m., the early joggers, commuters and yoga students have melted away before the arrival of the walkers, heading up through Chelsea or down to the Meatpacking District. They stop like currents in an eddy for a while, or they find a grassy backwater, but mostly they go with the flow. The polyglot visitors find a trendy destination, the natives a transcendental sidewalk that stretches a mile and a half, now that the third and last segment opened this fall.

The path narrows to just a few feet for much of its course, yet almost 5 million visitors pass one another every year in relaxed good cheer. Just five years after opening, the High Line has become one of the top visitor attractions in New York — more popular even than the Statue of Liberty — and an emblem of the reversal in the historical decline of the American city in general and Gotham in particular.

It has become an archetype for cities everywhere craving their own High Line mojo. In Washington, it is the inspiration for a proposed elevated park where the old 11th Street Bridge crossed the Anacostia River and, separately, for a component in the long-range redevelopment of Union Station.

The reasons for its broad appeal are both tangible and elusive but reduce to this: The High Line serves up the Big Apple on a platter 30 feet high. Look eastward, and you can savor the view of Midtown’s iconic skyscrapers. Look west, and the Hudson River lolls by, black and sparkling in the autumn light. The High Line takes you, voyeuristically, past the windows of high-rise offices and apartments and, increasingly, close to the swanky condos rising around it. You can look down to the bistros of the once-gritty Meatpacking District, or the leafy cross streets of West Chelsea, or the ribbons of silver commuter cars in the Hudson Rail Yards.

Five years after opening, the High Line has become one of the top visitor attractions in New York and an emblem of the reversal in historical decline of the American city in general and Gotham in particular. (Adrian Higgins/The Washington Post)

For all the attention-grabbing vistas, the focus eventually settles on the park’s interior character. It is a runway where people go to see and to be seen, like a return to the 19th-century promenade — synonymously a place and an act, where generations past put on their Sunday best and headed to the park, not to walk but to strut.

And while the High Line propels movement, “that doesn’t necessarily mean getting from here to there,” said Chris Reed, a landscape architect who teaches at Harvard’s Graduate School of Design and who takes students to the High Line. “The act of the promenade is something we lost in the 20th century, and a project like this allows us to focus on just that, the experience of movement.”

The idea of reusing old transportation corridors is not new — in Washington, the C&O Canal, and the Capital Crescent and W&OD trails, are obvious examples of such reincarnations. But the High Line’s success has been so swift that its success appears in hindsight to have been preordained. This would be a misread.

From rail cars to wildflowers

After the last train squealed its way along the tracks in 1980, the High Line became just another peeling grave marker to old, working New York. In time, the rails took on a mantle of rust, and the rotting ties and track ballast turned into a growing medium for weeds. Some of the weeds took the form of pretty wildflowers — goldenrod, milkweed and Queen Anne’s lace; some were thuggish trees and vines. Together, though, they imprinted the idea of vegetation turning the High Line into a garden, however feral, apart from the city.

Robert Hammond and Joshua David, two civic activists who saw this potential, formed Friends of the High Line in 1999 and battled to save it. Over time, they marshaled the civic and economic forces necessary to succeed.

The first two sections, which opened in 2009 and 2011, run 20 blocks, from the Meatpacking District north through West Chelsea, and cost $152 million to design, engineer and reconstruct. The new phase, called the High Line at the Rail Yards, which officially opened in September, initially cost $35 million, though it is a scaled-back segment that will be structurally rehabilitated in about a decade as the adjoining rail yards become the platform for a whole new skyline above them.

The costs may seem high, but as the architects and landscape architects got down to work, they discovered that much of the infrastructure needed major renovation. The High Line is, essentially, an elongated rooftop garden, where the depth of the (highly engineered) soil is measured in inches rather than feet, and elaborate stormwater-management and irrigation systems lie hidden from view.

Another view of the High Line in New York City. (Adrian Higgins/The Washington Post)

The clients — the Friends group and the city of New York — chose landscape architect James Corner Field Operations and architects Diller Scofidio + Renfro to lead the design. The force behind the park’s formidable horticultural presence is a Dutch plant designer named Piet Oudolf.

Together they have leavened the directional nature of the experience through planting effects, including passages through woodland motifs, and with design elements in broader parts that offer places to sit, view commissioned sculpture and other art, watch performances, and generally experience urban culture while floating above the city.

The first section also contains a small, squared-off amphitheater whose stage is a glass viewing wall down to 10th Avenue, where Manhattan’s surly traffic is tamed as a form of animated entertainment.

The second segment is especially rich in its horticultural effects — a tunnel of trees called the Chelsea Thicket opens to a popular resting spot, with a lawn and banks of seats.

Keep going and you pass through an idealized and richly planted herbaceous meadow, until the line arcs westward to the new segment past the elegant lines of the Radial Bench.

The underlying design philosophy of the whole High Line, James Corner said, was to recognize the sheer power of its passage through the city and the drama of its years in the wilderness. The new section features a discrete children’s play area, but the High Line is free of dog runs, playgrounds and conventional park planting schemes. Bikes, skateboards and cigarettes are banned. The plants, now maturing, give the High Line its singular spirit.

“We wanted a wild, dynamic landscape that was interesting not just in winter, spring, summer and fall, but almost every week having different blooms and colors and textures and scents,” Corner said.

Beyond the average shrub

Piet Oudolf, the plant designer, turned 70 in October but has a timeless, rugged look about him that suggests a Viking elder. His passion for perennials and ornamental grasses was informed by German horticultural researchers and has been honed over a lifetime as a nurseryman and plant designer. He works out of his farm and trial gardens in the Netherlands, and is a well-established leader of a naturalistic movement in gardenmaking that is ecologically informed but artistically driven.

Among his high-profile commissions in the United States have been the Lurie Garden in Chicago, Battery Park in Lower Manhattan and, at the New York Botanical Garden in the Bronx, the Seasonal Walk. He has yet to do a major project in Washington.

To achieve the dynamic qualities he is known for, Oudolf taps uncommon plant varieties and groups them in rich layers. This bestows them with texture, volume, movement and a vitality that persists after the top growth dies back at this time of year.

“I want to show the world there’s more than the average shrub,” he said. “I never go for the average.” Even plant geeks are caught off guard by some of his choices.

Todd Forrest, vice president of horticulture at the New York Botanical Garden, said he was astonished to find on the High Line plantings of a wildflower from Arkansas named Penstemon cobaea. “I thought this was great — in the most highly designed of locations, you find a true curiosity.”

Oudolf also used an enveloping tunnel of bigleaf magnolia, a junglelike tree native to the eastern United States and hardy, but rarely planted outside arboretums.

In what’s known as the Wildflower Meadow, Oudolf developed a matrix of Korean feather reedgrass that slowly yields to a matrix of switch grass. Both are heavily interplanted with clumps of perennials chosen for their late season of bloom and interest.

The success and high profile of the High Line have served to put the practice of landscape architecture, so often overshadowed by architecture, into the limelight. The sophistication of the plant designs is undoubtedly lost on the great majority of visitors, but the effect — of a restless, changing, naturalistic form evoking the original wildflowers — is not.

“It should take you in, and you don’t have to know about plants,” Oudolf said. “You have to feel it.”