"Seven or eight, depending on how you count them, including the houses," says Paul Turner, a professor emeritus in architectural history at Stanford. He’s the author of "Frank Lloyd Wright and San Francisco," a book that’s as much about the projects that didn’t get built as the ones that did.

"Frank Lloyd Wright actually designed close to 30 projects for the Bay Area, and they include some of his most unusual and really amazing buildings," he says.

Why did Wright’s proposals fail to get the go-ahead? A lot of times he was just dreaming too big (read: expensive) for the client. But that didn't stop him from dreaming big.

"For example, his first skyscraper was designed for Market Street in San Francisco," Turner says. "If there were some project that he found interesting, he would do the design and just hope that it would get built."

Wright never got the commission for a San Francisco skyscraper. Just as he never got a commission to design another Bay Bridge.

There was talk of a second span almost as soon as the Bay Bridge was completed in the 1930s. That's right: Traffic was that bad, that early.

In the late 1940s, Wright was competing for projects all across the country. Jaroslav Joseph Polivka, a San Francisco Bay Area engineer and fan of Wright’s, suggested he throw his hat in the ring for the proposed second Bay Bridge.

That was in 1949, and Wright would spend the last decade of his life trying to win over decision-makers in California. Essentially, he fell in love with his own proposal, which he called the “Butterfly Bridge.”

"The structure had the form of a thorax and wings of a butterfly in reinforced concrete. It’s a beautiful sculptural form when you look at the drawings that he did of it," Turner says.

The Butterfly Bridge would have started on the San Francisco end of the bridge, at the terminus of Army Street, now Cesar Chavez. Long, curved, concrete arms stretch across the water toward Oakland, carrying six lanes of traffic and two pedestrian walkways.

The literal centerpiece of the bridge: a hanging garden.

"People driving across the bridge could pull off into this landscape park and enjoy the views from high above over the bay. It’s kind of a crazy idea that traffic going across the bay could stop and there would be enough room for parking and everything, but that was the idea," Turner says.

The idea doesn't sound too crazy to me. After all, the Golden Gate Bridge is a tourist destination as well as a throughput for traffic. The proposal for the Butterfly Bridge was received enthusiastically by the San Francisco press. But the state Assembly Committee rejected the plan, influenced by consulting engineers dubious about the details.

"The engineers in Sacramento were able to say, 'Well, it’s just not worked out in enough detail. We don’t think it’s going to work. It’s too radical,' " Turner says.

To be fair to the pencil pushers in the state Capitol, Turner adds we have to imagine how things looked back in the mid-20th century.

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"The idea was so unusual, was so radical, it was unlike any earlier bridge that had been designed," he says. "And because Wright had not gotten a commission to do it, wasn’t being paid anything, they weren’t able to design the bridge in the kind of detail that would really be required, with all of the structural analysis and everything. That would have to come later."

Ultimately, they decided it wasn’t necessary because a few years later, people started talking about BART under the bay, and so that became the solution to this traffic problem.

Wright called that idea “suicidal,” which turns out to be an overstatement as the Transbay Tube is still going strong after more than 40 years.

In the end, Wright died, and with it, serious thoughts of doing something with his plans. Especially after the new, expanded San Mateo Bridge opened in 1967.

People still talk of building another bridge to span the bay. Just last December, Sen. Diane Feinstein and East Bay Rep. Mark DeSaulnier called for another bay bridge, a so-called “Southern Crossing” south of the Bay Bridge.

"Every now and then, people talk about an extra possible bridge and there’ll be stories in the newspapers. So it still captivates the imagination of the public because it is so beautiful," Turner says, sighing.

So what does Duncan Keefe of San Jose think? Should we resurrect Frank Lloyd Wright’s Butterfly Bridge?

"As much as I would have liked to see this bridge have been built, it was for a different time. These days, if we’re going to make any investment, it ought to be in getting trains across the bay, not cars. We have enough cars already, and you know, throwing more cars across the bay is only going to make the traffic situation on the Peninsula and in San Francisco even worse," Keefe says.