If all goes as planned, Midtown Manhattan will soon add a high-rise to its skyline substantially taller than the Empire State Building. In exchange for the gargantuan skyscraper, commuters would receive some $210 million of improvements to Grand Central Terminal, easing congestion. This pact would not only serve as a towering example of how cities rely on partnerships with the private realm to build civic spaces, it would also demonstrate how these arrangements influence the very projects architects design.

Over the past two decades, cities across the country have been turning to the private sector to help build schools, libraries, parks, and infrastructure. In recent years, the practice has become almost commonplace as municipalities grapple with budget shortfalls, high land prices, and a public that bristles at tax hikes. Today, the average American city relies on the private sector to help it perform a third of its municipal services, according to the National Council for Public-Private Partnerships, a nonprofit group. That proportion is sure to grow.

While citizens come to grips with existential questions about the risks and benefits of ceding the public arena to private industry, architects face challenges of their own. Public-private partnerships take countless forms and are invariably complex, borne of meetings and scrutiny that can last years. In many cases, designers find themselves shepherding a project for long stretches and assuming nontraditional duties along the way, like writing grants or navigating the rules of regulatory agencies. But the payoff can be sweet: a successful partnership can present an architect with a unique opportunity to build something that would never have existed otherwise. "These things are amazing professional bandwidth stretchers," says Gullivar Shepard, a principal at New York-based landscape architects Michael Van Valkenburgh Associates. "It's fascinating to learn about how the world works and not be in a design box. It gets very stuffy in there."

A Partnership by Design

One Vanderbilt, the office tower planned for Midtown Manhattan by Kohn Pedersen Fox (KPF), would rise 64 stories'twice the size permitted'if it wins city approval this spring. In exchange, commuters would get an array of improvements to Grand Central next door, including a public waiting room in the tower's lobby, an underground pedestrian corridor connecting the building to the terminal, as well as new elevators, stairs, and subway entrances. The developer, SL Green Realty Corp., would also build and maintain an adjacent pedestrian plaza.

The proposed partnership would not only deliver the public concessions, it would also affect what the glassy 1,500-foot-tall building, with 1.6 million square feet of leasable space ultimately looks like. The architects designed its tapering tower, for example, to fulfill requirements to protect sightlines to the Chrysler Building. The partnership "redefined the project from the get-go," says KPF president James von Klemperer. The architects considered an alternate design without the public component, which yielded a 30 percent smaller building that lacked the subgrade connections and the plaza. "It was an entirely different ilk of project," says von Klemperer.

The public, however, has been a reluctant stakeholder. The two community boards that represent the neighborhood rejected proposals to rezone the site, pointing to concerns that the deal could shortchange the people. But community boards are advisory bodies, and their resolutions are not binding. Ultimately, the City Council will determine the fate of One Vanderbilt. "Very often, they [public-private partnerships] are done in such a way that the public doesn't benefit," says Stanley N. Katz, the director of the Princeton University Center for Arts and Cultural Policy Studies. "More than anything else, it is a subsidy to the developer."

KPF had unsuccessfully attempted to win the community boards over, inviting members to the company's offices. "The architect's job is not just to solve problems—it's to be a bit firm at the right times, to make a strong argument," says von Klemperer. "Without strong ideas and a strong reputation that wins over your client—and, in a way, your public client—then your buildings won't be of much value."

The plan does have the support of Mayor Bill de Blasio, whose administration is simultaneously pushing a plan to rezone five blocks of the immediate neighborhood to allow larger buildings in exchange for amenities. Having the city on your side can prove instrumental. "You're not alone at the podium when you're trying to explain the transaction in a public forum," says Mary G. Murphy, a partner at the law firm Gibson Dunn who has negotiated numerous public-private partnerships in the San Francisco Bay Area.

Friends and Public Spaces

In some cases, private citizens lead the charge, organizing communities to turn fallow land into a public amenity. In Austin, Texas, a $147 million public project to divert floodwater from downtown paved the way for the restoration of Waller Creek, which winds through the city center. Now the nonprofit Waller Creek Conservancy (WCC) is working with Michael Van Valkenburgh Associates and Thomas Phifer & Partners to restore the creek, connecting existing parks along the 1.5-mile stretch and adding new ones.

Supporters of Waller Creek point to the creation of a nonprofit conservancy as the reason that the park might finally materialize. Unlike a city agency that has a narrow mandate—to build city parks, etc.—a nonprofit can be nimble. If it handles maintenance, for example, a designer could use costlier materials like wood for benches, which might be too cumbersome for a city agency to maintain. "Public entities have so many varying commitments citywide that they tend toward regulation and similarity," says Peter Mullan, the chief executive officer of the WCC. "When you have something that requires anything but that, a standardized solution is difficult."

In recent years, these sorts of partnerships have led to some innovative designs, such as the proposal to build Pier 55, a $130 million park-and-performance space that would replace a derelict pier in downtown Manhattan. "When you look around, the more unique spaces are being built with private money," says Madelyn Wils, the president of the Hudson River Park Trust, the city-state organization that oversees the pier. IAC chairman Barry Diller and his wife, designer Diane von Furstenberg, are not only bankrolling most of the project, but also spearheading it. The Trust first approached Diller in 2012 with a proposal for a modest, curvaceous park pier. Diller rejected the idea, selecting Heatherwick Studio to design an undulating cultural island with mushroom-shaped columns, tree-shaded footpaths, and three performance spaces. Diller has been "deeply involved" in every step of development, according to Signe Nielsen, a principal at Mathews Nielsen, the landscape architect for Pier 55. "While they don't weigh in on every single detail, they weigh in on those things that matter," she says.

For two years, the Trust honed the design with Diller before announcing it to the public, sparking outrage from critics, who characterized the plan as a backroom deal shrouded in secrecy. "Decisions about what ought to be done with public space ought to be public decisions," says Princeton's Katz. "The fact that the super-wealthy can purchase those decisions makes a huge difference in the way we behave."

Not All Solutions Are Private

A 2011 proposal to build a two- or three-story addition atop the Mies van der Rohe-designed Martin Luther King Jr. Memorial Library in Washington, D.C. (the architect's last building, completed posthumously in 1972), was certainly ambitious. The library would have rented out the new space, using the revenue to subsidize a renovation of the existing building. But the trustees abandoned the plan earlier this year, after an appraisal found that it would generate minimal revenue and overly complicate the project. Instead, the city's capital budget will finance a $225 million expansion and renovation by Dutch architects Mecanoo Architecten and the Washington, D.C., firm Martinez+Johnson. A one-story addition aims to bring light and air into the building. "We decided it was better for the library to go it alone," says Richard Reyes-Gavilan, the library system's executive director. "It would have been exceedingly difficult to maintain the integrity of this landmark and build up three floors."

In fact, Washington, D.C., has almost never turned to the private sector to renovate or build its libraries, instead relying on city funds for construction, including those for two libraries designed by David Adjaye. "Overwhelmingly, the residents of the city and library users don't think libraries or recreation centers should be privatized,"says Robin Diener, director of the D.C. Library Renaissance Project, an advocacy group.

The exception is the West End Library in D.C.'s wealthy Foggy Bottom neighborhood, part of a larger development designed by New York firm TEN Arquitectos on partly public land. Construction recently began on a $215 million mixed-use project there that will include 164 market-rate residential units built atop a 20,600-square-foot library with retail. On a separate parcel, the developer, EastBanc, will build a fire station, athletic facility, and 61 units—all but six affordable. (In exchange for the public land, a team led by the developer agreed to build the fire station and the library, a $25 million investment.) The city provided a $7 million low-interest loan for the affordable units. Public-private partnerships "are much more complex, but they bring up other opportunities that end up being really good challenges," says TEN Arquitectos' Enrique Norten.

The project took more than a decade to break ground. A 2007 city proposal to put the land out for bid fell apart, delaying the project until 2010. After EastBanc was awarded the site, the D.C. Library Renaissance Project, which is backed by consumer advocate Ralph Nader, lambasted it as a sweetheart deal that gave away public land to a private entity. As a result, the project was tied up in litigation for nearly two years until an appeals court threw out the case last spring.

The Only Way Forward

Sometimes a partnership is the clear option. The Port of San Francisco, for example, maintains the city's ports, like the famous Fisherman's Wharf and Pier 39. Some of the piers are deteriorating and used for municipal parking, as saltwater relentlessly penetrates the piles. In recent years, the Port has turned to the private sector to pay for their restoration. In exchange, the Port gives the private entities incentives, like the chance to rent public waterfront land at a steep discount.

In 2013, the Exploratorium, a beloved science museum, opened its new location on Piers 15 and 17 near the Embarcadero. The design by the San Francisco firm EHDD created a 330,000-square-foot campus with a renovated shed and a new two-story glass pavilion that houses a restaurant and bay observatory. The deal that was hammered out with the Port gave the museum (a nonprofit) rent abatement in exchange for rehabilitating the aging bulkhead and rebuilding a pavilion. "What the Port gets is an important historic structure that is maintained and made available to the general public, that wasn't before," says Byron Rhett, the deputy director of planning and development for the Port. The museum gets 50 years of free rent.

The $300 million project was financed with private donations. The biggest challenge was restoring the integrity of the pier: for the first year of construction, 30 divers timed their work with the tide cycles. The designers and the museum also had to deal with myriad state and city agencies that restricted the use of colors, signage, and windows on the historic structure. And because the pier is state land, there had to be some public access. "A lot of agencies had to give us permission to do what we needed to do," says Marc L'Italien, a principal at EHDD. "There is a science to all that. Typically, as architects, that is not our forte."

And on East 57th Street in Manhattan, a public-private partnership allowed developers to build on a parcel of city land that was previously underdeveloped. The result was something that neither the private sector nor the public could have done on its own. Over a period of a decade, the developer, World Wide Group, worked with Skidmore, Owings & Merrill (SOM) to build three public schools, a Whole Foods Market, and now a 65-story residential building that is the last piece of a complex puzzle. "The city benefited tremendously by getting three beautiful schools on time, on budget, and off their books," says Julia Hodgson, the director of development for World Wide. "What we got was a site that was otherwise unavailable."

The model seems to be taking hold. In 2012, the City of New York released requests for expressions of interest for three similar Manhattan sites for developers to rebuild aging schools in exchange for development opportunities. As cities turn to these partnerships on a regular basis, architects and designers may find their place in the process shifting as well. "Our role is to act at some level as the arbiter between the public interest and the private interest," says Vishaan Chakrabarti, a principal at SHoP Architects, which has been involved in numerous public-private partnerships, including the transformation of the Domino Sugar Plant in Brooklyn into a 3.3 million-square-foot mixed-use development. "We put flesh on the bones."

Freelance journalist Ronda Kaysen writes the Ask Real Estate column for The New York Times.