MANHATTAN:ON A SUNNY summer's evening, the High Line is almost as close to heaven as you can get in Manhattan. Once an elevated railway transporting goods to and from the Hudson Yards, it lay abandoned for years before undergoing a remarkable transformation into New York's favourite linear park.

Stretching from Gansvoort Street to 30th Street, the High Line has become the hippest thing on the west side of Manhattan. Now the Lower East Side is responding with a radical proposal for the world’s first underground park, in a former trolleycar depot beneath Delancey Street – it’s being called the Low Line.

Designers Dan Barasch and James Ramsey have pioneered the idea of using solar collectors at street level to gather sunlight and transmit it via fibre-optic cables to diffusers underground, creating an environment for plants and trees to flourish in the cavernous trolleycar depot (its floor-to-ceiling height is six metres).

With 1.5 acres of space, it would undoubtedly be New York’s most unusual pocket park. “Of course, the lighting will be supplemented with an electric supply at night and during cloudy periods . . . and we’ll also need additional energy for a ventilation system,” Ramsey says, adding this would be “as green as possible”.

Through Kickstarter.com, the pair managed to raise $150,000 (€120,000) to build a "mini-Low Line" – a model to show how the venture would work. "We're doing all we can to build community support, from every small business, real estate owner, local resident, student, or artist to all elected officials," Barasch told Yahoo. They already have backing from New York's Metropolitan Transit Authority, which owns the one-time trolleycar depot, which had a very short life; it was created in 1903 to serve trams coming from Brooklyn over the Williamsburg Bridge and was abandoned in 1948. The vestiges of its former use are still there, however.

“We fell in love with the site because of its architectural details: old cobblestones, crisscrossing rail tracks, vaulted 20-foot ceilings and strong steel columns,” says Ramsey, an architect who heads Raad Studio, a design firm based in nearby Chrystie Street. Barasch, who runs the project, has worked for Google.

The site is in the heart of the Lower East Side, not far from Chinatown and Little Italy, which is now an up-and-coming area. “Our neighbourhood is one of the oldest in the US and has been home to generations of immigrants for centuries. It is a centre of diversity, culture, creativity and innovation,” they say.

They’ll need serious sponsorship to turn their vision of the Low Line into reality. It was only after significant funding was pledged by a foundation headed by New York fashion designer Diane von Furstenberg and her husband Barry Diller that the first phase of the High Line got off the ground in 2005.

Since then, the couple have stepped forward to provide funding for the second and third phases, subscribing a total of $35 million (€28 million). But then, von Furstenberg’s faceted-glass penthouse sits on top of her fashion empire’s headquarters in the Gansevoort Market Historic District, overlooking the High Line.

As architecture critic Paul Goldberger has noted in National Geographic, the line’s transformation into a public amenity was little short of miraculous. Former New York mayor Rudy Giuliani “couldn’t wait to tear it down”, as his administration saw this crumbling urban relic as an impediment to gentrifying the Chelsea area.

“Never have public officials been so wrong. Almost a decade after the Giuliani administration tried to tear the High Line down, it has been turned into one of the most innovative and inviting public spaces in New York city and perhaps the entire country . . . part promenade, part town square, part botanical garden.”

The great attraction of the High Line is its elevation nearly eight metres above street level, which gives users a sense of floating in space as they walk along it, amidst the amazing variety of plants, sniffing the scent given off by drifts of lavender, or loll about sunbathing on the lawn above 23rd Street.

It might never have happened but for the vision of freelance writer Joshua David and artist Robert Hammond, both of whom lived in the area and were fascinated by the potential of this hulk from another era. They formed Friends of the High Line in 1999 and spearheaded a campaign to save it from the threat of demolition.

Friends of the High Line is a non-profit conservancy working with the New York City Department of Parks and Recreation to maintain it as an “extraordinary public space for all visitors to enjoy” – and this, being the US, includes raising private funds to cover most of its annual operating costs and public art programming.

High Line Art currently features a exhibition called Lilliput (the name borrowed from Jonathan Swift’s Gulliver’s Travels), featuring a series of miniature sculptures “installed in unusual and unexpected places along the High Line – amongst the vegetation and along the pathway – to create an art treasure-hunt for visitors”.

Beautifully paved in stone, with remnants of the railway tracks retained, it is straddled by several buildings including the trendy Standard Hotel, where floor-to-ceiling windows have been used by exhibitionists to engage in public sex. Further along, a naked man appears to wave from a window – but it’s a painting.

It’s a mark of the affection for the High Line that it has been virtually crime-free since it opened – no doubt aided by CCTV cameras and restricted opening hours – it closes at 11pm in summer. On its second anniversary last June, the police department said there had been no reports of muggings or other significant crime.

Designed by New York-based landscape architects Field Operations and architects Diller Scofidio + Renfro, with planting by Dutch garden designer Piet Oudolf, the linear park is such a hit that developers have been scrambling to build apartments alongside it. “Live artfully steps from the High Line,” one of their billboards says.

“Think the High Line is cool? Check out our roofdeck,” says another. Right at the end of it, Hudson Yards is billed as “New York’s next great neighbourhood” – the biggest comprehensive redevelopment scheme in the city since the Rockefeller Center; it will include 2.4 million sq m of office space and 20,000 apartments.

Last April, Friends of the High Line racked up an important victory when the New York City Planning Commission unanimously approved a zoning amendment that will secure the remaining undeveloped section of the disused railway as public open space – and imposed a levy on the developers to cover 30 per cent of its cost.

This will be the final phase of extending the linear park from the old meatpacking district around 12th Street all the way to 34th Street – a remarkable achievement. Whether the much smaller but technically challenging Low Line project sees the light of day is an open question at this stage. It certainly deserves a whirl.

See thelowline.org and thehighline.org