BOSTON - For more than two decades, the words Big Dig were a virtual epithet, a sort of national shorthand for pork-barrel extravagance, skillful political earmarking, cost overruns, and government bumbling.

But now that Boston's decrepit, elevated Central Artery has been carted away and replaced with a 10-lane underground tunnel that allows traffic to glide silently below downtown's streets, the $14.8 billion price tag and associated scandals are receding in the city's memory.

Today, the Big Dig looks more like Boston's Big Coup.

On a bright morning in the fall, Boston dedicated a 1.5-mile linear park that is the public face of the Big Dig. A series of connected lawns and gardens, the greenway hugs the contours of downtown, skirting the historic Quincy Market and opening up spectacular views of the South Boston waterfront. Once an outback of crumbling warehouses, wharves, and parking lots, the area is morphing into a glittering arts district. The city is visibly whole again.

Covetous glances are being cast from Philadelphia, another city long separated from its waterfront by an interstate highway.

Not long ago, the idea of bringing down the great barrier of I-95 seemed beyond Philadelphia's reach. But in recent months, a group of influential Philadelphians has been talking seriously about embarking on a "Philly Dig." They are emboldened not just by Boston's success, but also by President Obama's emphasis on stronger infrastructures and Mayor Nutter's interest in developing the historic waterfront.

"This is the time to be ambitious," argued Gary Hack, an internationally recognized urban planner and former dean of University of Pennsylvania's School of Design. "If Philadelphia had a plan ready for I-95, we could probably be starting something right now."

Striking the highway from the city map was once dismissed as the idle fancy of urban planners and waterfront activists. But in the next decade or so, the most intrusive part of I-95, the 30-year-old Penn's Landing segment, will reach the end of its functional life and require a reconstruction.

"The question we should be asking right now is: Do we rebuild I-95 as is, or do we rethink the whole thing?" said Harris Steinberg, who runs the nonprofit consulting firm PennPraxis, which developed a waterfront policy for the city in 2007. The Obama administration's interest in urban areas, he said, "has given the city a license to do something bold."

Actually, what Hack and Steinberg envision is less a Big Dig than a No Dig.

Instead of burying the highway in an expensive tunnel, they would entirely rip out a stretch of I-95 that runs south of the Ben Franklin Bridge and I-676. Traffic volume drops off there, proponents argue, because the bulk of the highway's users are commuting into Center City from the north. Airport travelers, they point out, can take I-676 to I-76.

With I-95 out of the picture, cars would flow along the Delaware River on Columbus Boulevard. That road would still give drivers access to Penn's Landing, the South Philadelphia retail chains, and the sports complex. But drivers would be traveling on a city street bounded by sidewalks and bike lanes and regulated by traffic signals. The highway could pick up again around South Street, or perhaps Washington Avenue.

The transition would be similar to what happens near Cape May where the Garden State Parkway downsizes to a local boulevard.

Opponents, who include planners and traffic experts, point out that tie-ups can overwhelm the southern end of Columbus Boulevard, near the big box stores. But Philly Dig supporters maintain that problem is manageable.

Unlike Boston's Central Artery, the central part of I-95 between Market and South Streets runs in a trench. Since the trench is roughly the width of a Philadelphia block, eliminating the interstate would enable the city to stretch its street grid farther east. The land could slope gradually down to level of the river.

For motorists, driving on a boulevard would certainly be slower and more cumbersome than zipping along on an interstate. But the trade-off, proponents argue, is that the Delaware River would become more accessible, especially for pedestrians.

Once the wide highway is gone, large-scale waterfront development would finally make sense. The city would gain about six blocks of tax-producing real estate, which could be sold to private developers for additional revenue.

The concept is getting lots of encouragement from outsiders. During a speech to the Ed Bacon Foundation in December, John O. Norquist, the head of the Congress for the New Urbanism and a former Milwaukee mayor, told Philadelphians that I-95 was expendable. "Get rid of it," he urged.

Alex Krieger, a Harvard University urban planner who prepared the initial design for Boston's new greenway, contends that removing I-95 would be a modest undertaking compared with the Big Dig. While Boston needed almost four miles of underground tunnels and costly ventilation systems, Philadelphia would need only to take a jackhammer to roughly a mile of I-95.

"Philadelphia's problem is a lot easier to solve than Boston," Krieger said. "It's not such an incredible engineering challenge."

In many respects, what Hack and Steinberg propose is more like San Francisco's Embarcadero, a palm-lined boulevard that follows the bay and connects the waterfront to the downtown. San Francisco's dig came about by chance, after a 1989 earthquake destroyed its freeway.

Although the idea of tearing apart part of I-95 was first floated almost a decade ago, the stars seem finally to be aligning. This summer, Philadelphia will select a firm to prepare a detailed master plan for the central Delaware. Some of the world's best-known planners are angling for the job.

Alan Greenberger, the city's planning director, said the winner would be expected to offer scenarios for dealing with I-95, especially the trench section. It would be the first serious analysis of the city's options since the interstate separated Center City from its waterfront in 1979.

"To tell you the truth, I don't think the consultant is going to come up with any new ideas. I-95 has been looked at so many times already," Greenberger acknowledged. "What we're hoping is that they'll be able to create a consensus for one approach."

Ironically, some of the strongest opposition to a Philly Dig comes from Rina Cutler. Now the city's deputy mayor for transportation, she was Boston's transportation director when the Big Dig began.

While Cutler concedes that the Big Dig "is an amazing engineering feat that will succeed in knitting the city back together," she argued that the Massachusetts Turnpike Authority is burdened with huge debt from its share of the project. "It can't afford to fix anything," she said.

As Philadelphia embarks on the master plan for its riverfront, the challenge will be to provide a hardheaded assessment of the costs and benefits:

Will getting rid of I-95 really yield the promised development?

What costs will the city and state have to bear if the federal government doesn't fund the reconstruction?

And can Columbus Boulevard really handle the extra traffic?

Barry Seymour, who heads the Delaware Valley Regional Planning Commission, doesn't think so.

"Our take is that the volume is still significant going south. Delaware Avenue couldn't handle all the traffic," he said.

In Boston, the planning community is only just beginning to acknowledge that the Big Dig was worthwhile. October's ribbon-cutting for the greenway seemed as close as Boston had come to celebrating the end of the 22-year project.

Response to the park has been lukewarm. Its block-long segments often feel purposeless and empty - much like Independence Mall before its reconstruction. And the landscaping is decidedly second-rate.

Many Boston planners believe that the park hasn't caught on because it is too big and spread out. During the heated debates over the Big Dig construction, Massachusetts announced it would devote 75 percent of the land on top of the tunnel to open space. Today, many planners agree that Boston would have been better off with more buildings and less green space.

"The park totally lacks definition that you get from buildings," complained Thomas Piper, a professor of planning at the Massachusetts Institute of Technology. More density is needed to close the gap between Boston's downtown and its newly accessible waterfront.

Officials at the turnpike authority suggest that the necessary density is just a real estate boom away.

"We need to be patient," said turnpike chief Jeffrey Mullen. "I think we're looking at some of the most valuable real estate in the commonwealth." The authority estimates that the Big Dig has created the potential for $7 billion in construction and 43,000 jobs.

The Big Dig was never just about development, though. Its original purpose was to reduce Boston's famously incapacitating gridlock. Mullen said the new, wider underground tunnel had cut commuting times by more than half.

It wasn't until later that planners began to understand that the Big Dig would also help reintegrate Boston's storied Italian North End into the downtown fabric, said Rick Dimino, a former Boston transportation commissioner who runs A Better City, a nonprofit agency.

Burying the highway has also opened up thousands of acres in the old dock lands to development, he argued. Standing on the greenway, the area's new federal courthouse and new Institute of Contemporary Art beckon from across the channel.

"Taking down the elevated structure that was separating the waterfront from downtown was a renaissance event," Dimino argued. "It opened view corridors we're only beginning to feel and understand."

He and Mullen concede that the turnpike authority is still stuck with a massive debt. "But I think it would be wrong to blame the artery project alone," Dimino said. "We haven't raised the gas tax since 1991, and toll increases were deferred for years."

Cutler isn't convinced. "I can't really answer the question, 'Is it worth it?' The Big Dig wasn't done to knit back the city," she said. "It was done because rush hour was horrible."

Greenberger hopes the waterfront master plan will help break the impasse in Philadelphia. "I want the planners to tell us who is using this road, and do we really need it?"

"We understand," he continued, "that this is a balancing act, between the needs of traffic and the needs of waterfront development."

Cutler offered proponents this glimmer of support: "If an earthquake takes out I-95," she said, "I promise not to rebuild it."

Contact architecture critic Inga Saffron at 215-854-2213 or