The first piece of the Reading Viaduct rail park opens in June. Then what?

Back in the early 2000s, when the Callowhill neighborhood was a wasteland of shuttered factories, a couple of artists came up with a crazy plan to turn the abandoned Reading Viaduct into a park. New York's High Line hadn't yet opened, and few in Philadelphia could imagine the overgrown relic as a public attraction. Before the project even started, the noted architecture critic Witold Rybczynski penned a commentary in the New York Times advising cities not to waste their money on such follies.

Score one for the dreamers. Last week, the Center City District announced that the first phase of the Rail Park would open to the public in June. Although workers are still busy cutting fat planks of golden brown ipe wood for the boardwalk and smoothing out the surface of the main path, I decided to stop by and see how the long-awaited park designed by Studio Bryan Hanes was progressing. Rybczynski was right about this much: Transforming Philadelphia's industrial detritus into safe public space is an expensive and time-consuming undertaking.

It took more than six years and cost $10.3 million to build the park's first quarter mile, partly because of the need to cart away huge amounts of contaminated soil. Given the long struggle, the path through the space is appropriately meandering. From the main entrance near Broad and Noble Streets, the trail switchbacks past urban glades, clusters of benches, reimagined steel catenaries, and a public art sculpture that resembles (much too literally) a telephone pole. After a 10-minute ramble, I reached a row of charming, sofa-sized swings that offer 360-degree views of the fast-gentrifying Callowhill neighborhood. Behind them, at the entry to the main viaduct, stood two sturdy steel gates.

And that, folks, is the end of the line. At least for now.

As the city prepares to mark the opening of the elevated park, the groups behind the project — the Friends of the Rail Park, the Center City District, and Department of Parks and Recreation — are trying to figure out what happens next.

The segment that will be completed in June is a mere 1,300 feet in length, but the Friends of the Rail Park has always envisioned something much more ambitious. Their master plan calls for a three-mile trail that will loop around the northern rim of Center City, allowing people to walk from the viaduct's terminus at Ninth and Fairmount, west to 31st and Girard. If the group can pull it off, the completed Rail Park could help connect a string of neighborhoods between Chinatown and Brewerytown, and provide a green escape for their residents. But they will have to raise vast sums of money to make the bigger park a reality, well over $100 million.

In some ways, the threat to the Rail Park's western half is even more urgent. After the trail crosses Broad Street, it dips down below street level into in a trench that traverses the rapidly developing area north of the Parkway. SEPTA owns the trench, yet Michael Garden, the vice chair of the Friends group, told me that he worries about adjacent property owners building on top of the opening and choking the trail mid-run.

Last week, developer Tom Bock secured a construction permit to build a condo building behind the Rodin Museum at 21st and Hamilton, alongside the rail cut. He has told the group that he would consider leaving the trench open to the sky, but the issue isn't so simple. Because the Philadelphia Museum of Art fears that the building could overwhelm the famous sculpture gallery, designed by Paul Cret, it has been lobbying for changes in its building's size and siting.

It's not unusual, at least in Philadelphia, to build a park without knowing who will oversee its development. But if the Friends of the Rail Park hopes to deal with these challenges, Garden acknowledged, they're going to need a more formal structure to oversee the park's daily upkeep and plan its future. The group began as a grassroots organization, and it remains a volunteer group. When it came time to build the park, the group needed the Center City District to act as a kind of developer, securing the funding and managing the construction.

The new management organization could take a variety of forms. The city could create a business improvement district, similar to the Center City District, to oversee the Rail Park. But many Philadelphia's trails, like the ones on the Schuylkill and Delaware Rivers, are run by nonprofit development corporations.

Finding the right fit will be tricky. Garden believes it's crucial that the organization's primary mission be to serve the surrounding neighborhoods, rather than to promote development. Because of the need to constantly raise money, some park managers in Philadelphia are consumed with event planning. "We don't want the Rail Park to become a privatized events space, even if renting it out for events is a very attractive way to raise money," he added. Yet the organization will likely to need financial support from big property owners.

Whatever form they choose, the Rail Park is going to have to compete for a shrinking pot of government funding. Both Garden and Levy say they expect the next phase of the viaduct won't have the same fancy design finishes as the nearly completed section. They're looking into the possibility of simply paving an asphalt path down the middle and opening it to the public. And why not? Its wildness is a big part of its allure.

Philadelphians shouldn't expect the park's expansion to proceed in a strictly linear fashion. On the Schuylkill, the development corporation has constructed several independent parks along the waterfront to serve different neighborhoods. As it obtains grants, it is gradually knitting the pieces into a continuous trail.

The condo proposal for the area behind Rodin Museum site has forced the Friends group to consider a similar approach. Based on the developer's offer to keep the trench open, they are looking into the possibility of developing a one-block-long stretch of the Rail Park. Because of the way the sides of the trench slope down, Garden said it would be relatively easy to install an access ramp. With minimal landscaping, it could be transformed into a sunken garden.

With its proximity to the Rodin and the Parkway, it's the perfect site for such an experiment. Not only would the project advance the Rail Park, it would act as a proof of concept.

Many people — Levy among them — still aren't convinced a below-grade park is a good idea. "There's a whole different set of challenges there," he said. "Safety is one." But, as Levy acknowledged, he was once doubtful that an elevated park could succeed.

Parks take time to evolve. The High Line was built in three stages. Atlanta's Belt Line, another elevated rail park, has been in the making for over a decade. What the Rail Park will need most as it forges ahead are the dreamers who can keep its vision alive.