There's not going to be a giant fence surrounding the big Made in America music festival on the Benjamin Franklin Parkway during Labor Day weekend.

There will be two.

And city officials say that will be sufficient to provide concertgoers with a safe, enjoyable experience and to keep out those who don't buy tickets for the Parkway's first-ever paid event.

Twelve days before the first chord is to be struck, the City of Philadelphia on Monday released preliminary details about how the event will function and promised to release more throughout the week.

The two-day festival is set to bring as many as 50,000 people a day to the Parkway. Rapper, songwriter, and record producer Jay-Z headlines on Sept. 1, and Pearl Jam, the iconic Seattle grunge band, takes the lead on Sept. 2.

For Philadelphia, the festival offers a huge upside, including the potential to mark the city as a hip, urban backdrop for a cross-culture of major American music stars. It also brings risk, in the combustible combination of long hours, hot sun, and oceans of beer at the Budweiser-sponsored fest.

For the city, the concert represents a new breed of cat - smaller yet in some ways more complicated than previous jams, particularly in the creation of a huge perimeter around the festival grounds.

The boundary will run from the Art Museum north to Pennsylvania Avenue, southeast to 22d Street, south to Park Towne Place, northwest to 24th Street, north to Callowhill Street at Eakins Oval, and then west to the Art Museum.

That space will be surrounded by an 8-foot-high fence. Sixteen feet inside will be another 8-foot fence, this one covered with scrim, a lightweight fabric, to block people from seeing inside.

Police and private security personnel will be stationed inside and outside the fences. Signs will warn that attempts to climb or sneak past the barriers will result in arrest.

"This is a new thing for the city in some respects. It certainly is new on the Parkway," said Mayor Nutter's spokesman, Mark McDonald. Similar fencing has been used elsewhere, most notably at Lollapalooza in Chicago, he said.

The dual-fence system answers a key question surrounding the event: How are organizers going to enforce a ticket-holders-only entrance policy on the expanse of the parkway? And what will prevent non-ticket-holders from simply hanging around nearby to hear the show?

McDonald said some people might try to listen by standing near the exterior fence, but it would hardly be the same as being inside, because of the location of the stages and speakers.

High-powered acts include hip-hop superstar Drake; mega pop-star/singer/producer/DJ Calvin Harris; Skrillex, the electronic producer and DJ who won three Grammy Awards this year; Maybach Music, the alliance of hip-hop heavyweight Rick Ross, Washington rapper Wale, and Philadelphia's Meek Mill; and the resurgent soul man D'Angelo.

Also appearing will be rap godfathers Run-DMC; Brooklyn indie-rock band Dirty Projectors; genre-smashing avant-pop acts Janelle Monáe and Santigold; the controversial hip-hop collective Odd Future; and indie-electro band Passion Pit.

A spokesperson for promoter LiveNation said Made in America would offer music on four stages: one in front of the Art Museum steps, a second on the north side of the parkway, a third in the form of a giant electronic-dance-music tent on Von Colln Memorial Field, and a fourth, smaller "Heritage" stage on the south side of the Parkway.

With music aimed in several directions, the blended-together sound that might be heard outside the fence won't be very appealing, the spokesperson said.

Construction of the concert venue begins Thursday. The big challenge to motorists starts a week later, on Aug. 30, with street closures and parking restrictions that will run through Sept. 2.

"The City of Philadelphia has extensive institutional experience in managing large events on the Parkway and other sites in the city," Mayor Nutter said Monday. "Whether you are going to the festival or you want to visit our museums and other institutions on the Parkway, this Labor Day weekend in Philadelphia will be a great, fun-filled time for everyone."

The Art Museum and the Barnes Foundation plan to be open as scheduled during Labor Day weekend. Some neighbors and civic organizations have been nervous, as the start of the festival approached with no firm logistical details.

"I don't know who is in charge, and how it's going to impact us - we haven't been told," Bruce Butler, president of the Fairmount Civic Association, said last week. He said he hoped to get more information next Monday night, when some civic-association board members meet with police officials.

At this year's Welcome America Independence Day festival, chaos erupted near the Parkway when a 16-year-old boy shot two teenagers, the violence stemming from a neighborhood dispute. In 2011, rumors of a shots being fired caused a stampede that left Parkway spectators frightened, though no one was injured.

Performances on both days are scheduled to begin at 2 p.m. and end at 11 p.m., the concert to benefit United Way organizations in the Philadelphia region, South Jersey, Lancaster County, and New York City.

Oscar-winning director Ron Howard has been secured to film a documentary of the show.

One thing about Philadelphia, experts say, is this: The city knows how to put on giant public events, its track record reaching back to the 100,000-strong Live Aid concert at John F. Kennedy Stadium in 1985.

It handled the 2005 Live 8 concert that drew hundreds of thousands to the Parkway. And, of course, every July 4, the city stages the Welcome America extravaganza that draws half a million.

This audience will be limited to 50,000 each day - a fraction of some previous Parkway mega-events, and only a few thousand more than attend a typical Phillies game.

Huge outdoor festivals have been popular since the 1960s and, if anything, they're growing in popularity today. Dave Matthews played at wide-open Bader Field in Atlantic City last year, paving the way for this year's big Metallica festival there. The Firefly Music Festival in Dover, Del., spreads out across 87 acres of wooded grounds, Bonnaroo covers 700 acres in Tennessee, and the Coachella Valley Music and Arts Festival, commonly known as Coachellafest, takes place in the California desert.

Populous northeast cities often lack that kind of open space, but they do have many music fans. So promoters see a chance to plug a gap in the market - and make money. The challenge has been to identify urban spaces that offer room, access and the kind of iconic backdrop that only a big American city can provide.

The progress of Made in America is being followed by other organizers, including Jay Sweet, producer of the venerable, 53-year-old Newport Folk Festival in Rhode Island.

"If I were in Live Nation's place, I'd be communicating to every possible ticket-buyer or fan: Use public transportation, use public transportation, use public transportation," Sweet said. "Carpool. Bike. Take a bus. Do whatever you can to not drive."

Another recommendation:

"There has never been, in the history of events, someone who uttered, 'Oh, this place has too many Porta-Pottys,' " he said. "You cannot underestimate the fact, especially at a festival cohosted by a beer company, that the more people drink beer, the more they have to pee."

If he were running the show, he said, he would be thinking about all that could go wrong and trying to plan for those contingencies. What if a six-car wreck closes I-95 and people can't get to the show? What if the skies let loose a flooding rain, or lightning? Knowing how to evacuate 50,000 people is as important as knowing how to get them inside, he said.

David Fiorenza, an economist at the Villanova University School of Business who studies urban revitalization and arts projects, said that for Philadelphia, Made in America amounts to a bonus event, like an Eagles playoff game, generating additional revenue for the tax coffers and unexpected, end-of-season business for restaurants and hotels.

The show should draw from New York, Washington, and Baltimore, claiming entertainment dollars that might have gone elsewhere, and planting the thought with visitors that they should come back to Philadelphia on their next vacation.

One big upside, he said, is the city will collect wage taxes from every wealthy artist who steps on stage.

"Pearl Jam will be out 4 percent - and Eddie Vedder will complain to Rolling Stone next year," he said.

McDonald said that he had no immediate economic projections on whether the city will make or lose money, but that any cost should be balanced against the additional revenue that will flow to dining and retail establishments.

"The big benefit here is big cities do big things," he said. "And this is a pretty big one."

Contact staff writer Jeff Gammage at 215-854-2415,, or on Twitter @JeffGammage.

Inquirer music critic Dan DeLuca contributed to this article.