So watch out: There's another hairpin turn coming.

Seven years after Philadelphia engineers first trotted out a misguided plan to replace the decaying, but dignified, structure with a soulless, interstate-grade speedway, they've finally agreed to discuss design. A public forum will be held March 6 and 8 at the Philadelphia School. But whether the city gets the urban gateway it deserves remains a long shot.

The design forum, which comes about after a year of nagging by South Street community activists, does suggest a dawning recognition on the part of the city that this $54 million bridge project isn't primarily about moving cars efficiently. It's about forging a gracious, urban-scaled link between two vital neighborhoods, Center City and University City.

Neighborhood residents have argued for years that the new bridge should feel like the continuation of a city street, rather than a highway interloper in the style of the no-frills Walnut Street Bridge.

But it wasn't until November that architect James C. Campbell and former ward leader Terry Gillen were able to cobble together official support for a design charrette, an architectural-brainstorming session. Using state funds secured by Sen. Vincent Fumo, they've hired Wallace Roberts & Todd - the firm that assisted PennPraxis with its Delaware waterfront study - to guide the dialogue.

Campbell already has a laundry list of changes he believes would be easy to implement: Eliminate the dedicated turning lane. Use the gained space to widen the bridge's sidewalks from a stingy 9 feet to a comfortable 13. Reconfigure the corners so it's harder for a tractor-trailer to whip onto the Interstate 76 ramps.

And finally, dress the bridge in appropriate architectural clothing that reflects its true identity as an urban boulevard, one that just happens to be suspended over a gentle river.

Though city engineers say they're willing to consider ideas that bubble up during the charrette, it's unlikely they'll take up any suggestions. David Perri, the Streets Department official responsible for the project, says there's too little time and even less flexibility.

The crumbling bridge has been closed to buses and heavy trucks since last spring, and the city is intent on bidding the project by the end of March and starting construction in July. The Streets Department is certain to resist any costly design adjustments unless activists can pry additional money from government funding agencies.

That narrows the options, doesn't it? The only change Perri considers feasible is a reprogramming of the traffic lights to lengthen the crossing period for pedestrians.

So the odds are that the South Street Bridge will stand as a monument to a lost civic opportunity.

Because it is the southernmost of the Schuylkill's Center City crossings, it could have been - should have been - an iconic entry to Philadelphia and a magnificent podium for admiring the city's growing skyline. But the Street administration saw it only as a routine infrastructure project.

Here's a perfect example of where political leadership and strong city planning could have teamed up to make a difference. Instead, the bridge was farmed out to a firm that specializes in highway projects, Gannett Fleming. After it designed the bridge according to federal interstate standards, Gannett Fleming hired an architect, H2L2, to decorate it.

H2L2 is the successor firm to the one founded by the renowned Paul Philippe Cret, who designed the inspiring Ben Franklin Bridge with engineer Ralph Modjeski. The firm's architects say they are as disappointed with the look of the South Street Bridge as everyone else.

"It's essentially a highway overpass," designer James Templeton concedes. "We did a lot of sketches, but the city never saw them."

Templeton originally had grand ideas for the bridge that included glowing glass-paneled lanterns over the bridge piers, and sidewalk planters for trees. But, one by one, each grace note was eliminated. The glass was replaced with stainless-steel mesh, because that material supposedly requires less maintenance. Templeton said he was shocked to discover in the final rendering that the steel lanterns had been given four-cornered hats. It now looks as if giant tin salt shakers had been affixed to the bridge's sides.

In an ideal world, one can't separate a bridge's engineering from its architecture. We still marvel at the sight of a streamlined span jump-stepping over a broad river as if it were a mere puddle. When these structures fail, as the Minneapolis highway bridge did last summer, it makes us question the fundamentals of our society.

Even in its decrepit state, with hunks of concrete falling regularly into the Schuylkill, we still sense that the octogenarian South Street Bridge belongs to the noblest tradition of bridge-building. It's heavy enough to give us confidence in its ability to stand up to the elements, yet delicate enough in its detailing to put a spring in our step as we saunter across its pocked sidewalks.

But unless the engineers see the light during the design charrette, it looks as if we'll never walk that way again across the South Street Bridge.