"Light and sound" were going to "play on the graceful glass structure" of the Transbay Terminal being rebuilt in downtown San Francisco, according to the original plans. Artists' renderings show an undulating glass shell over the planned transit hub.

The originally planned glass exterior of the Transbay Terminal. (Transbay Joint Powers Authority)

But this week, as project organizers celebrated the groundbreaking for a neighboring glass tower, they also confirmed that the terminal itself may not be covered in glass after all — instead the shell will most likely be made of perforated metal.

The news of this change prompted a chorus of raspberries when San Francisco Chronicle urban design critic John King in the San Francisco Chronicle reported it earlier this month.

"Oh, cool. Drippy, dirty mesh," said one commentator on King's blog post.

"Bait and switch —promise one thing to get people interested and then back out giving some lame excuse," said another. "It's one reason that government and developers can't be trusted."

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The Transbay Joint Powers Authority is contemplating the change because in the final design stages it became clear that, well, glass breaks. And and earthquake or a bomb blast could create the mother of all messes.

An artist's conception of the possible perforated metal shell for the Transbay Terminal. (Transbay Joint Powers Authority)

"The second reason is cost," explained Maria Ayerdi, executive director of the TJPA. "It was going to be very expensive to put in the appropriate fixtures to hold up the glass and make it as safe as we wanted to make it."

Moving from glass to metal could save $17.5 million out of a total budget for the project of about $1.7 or $1.8 billion she said.

Construction costs stayed close to budget for years because the recession lowered demand. Now that's changed, with a couple of dozen cranes at work in San Francisco, said Ayerdi.

The designers haven't settled on a material yet. "We're examining several different choices from a clear anodized aluminum epoxy painted finish to a stainless steel in a matte finish for the exterior skin of the station," said Ayerdi.

"And we're looking at a number of different patterns from the worlds of science, math, engineering even art."

One possibility: an "aperiodic" patterninvented by Roger Penrose in 1966. "We want to find a pattern that will be educational to the public when they come and visit the station," said Ayerdi.

A rendering of a perforated metal design. (Transbay Joint Powers Authority)

The 40-acre project, bounded by Mission Street, Main Street, Folsom Street and Second Street, will provide a nexus for 11 transit systems, including several bus lines from around the Bay Area, including the bullet train being built to Los Angeles, the existing Caltrain, a shuttle to Amtrak, paratransit and a "people mover" like a moving sidewalk connecting underground to a nearby BART station, Ayerdi said.

There will be tracks available for Amtrak to steam directly into the station, too, if it gets the money together for that, Ayerdi said.

The originally planned glass design. (Transbay Joint Powers Authority)

And the terminal design still maintains one of its signature features, a 5.4-acre rooftop park.

But none of that is what city leaders were celebrating when they dug their shovels into the dirt on Wednesday, however. It was the TJPA's final sale of 101 First Street, a 50,000-square-foot parcel, to Hines and Boston Properties for $192 million.

That's the developer that plans to build a soaring monolithic glass tower on the site The 1,070-foot tower, designed by Pelli Clarke Pelli architects, will be the highest west of the Mississippi, with 60 stories of commercial space.

Both the tower and terminal are on track to be completed around the end of 2017, Ayerdi said.

The money from that sale and others are helping to finance the public transportation part of the project. And besides that, the tower is pretty, said Ayerdi.

The Transbay Transit Tower. (Transbay Joint Powers Authority)

"It's going to grace and redefine our skyline for generations to come. It's going to be a pearlescent luminescent color, a tall slender elegant tower that will anchor the Transbay Terminal station. It will anchor and mark the importance of transportation to the city of San Francisco and the Bay Area and the State of California."

Fine words. And you'd expect such praise from the public face of the project.

But San Francisco Joel Karr, a principal at Weske & Associates San Francisco architecture firm says they're not exaggerated. "It's really a powerful architectural statement and I'm excited to see it built," he said.

And he's not as upset as King's peanut gallery about the switch from glass to metal on the terminal itself. "I feel they've made an effort to retain those elements of light," he said.

Joel KarrJoel Karr

San Francisco Transbay Terminal Design May Change