When the traffic crawls to a halt on the eastern span of the Bay Bridge, more than a few motorists wonder: What if the "big one" strikes right now?

It's hard to ignore the fact that just north of the 71-year-old steel cantilever span sits its half-built replacement, scheduled for completion in 2013, 24 years after a 50-foot section collapsed in the Loma Prieta earthquake and killed a motorist.

That concern was even harder to suppress during Wednesday's rush hour, when car radios announced that the Interstate 35W bridge in Minneapolis suddenly gave way, pitching dozens of cars 60 feet into the Mississippi River.

Lamont Dill of Oakland said that when he heard the news, he thought, "that could happen anywhere," including the Bay Bridge he uses each day to get to his accounting job in San Francisco. After all, he reasoned, "We're due for a major earthquake."

But experts, as well as engineers at the state transportation department, Caltrans, are fairly certain that the bridge, and the other seven major bridges in the Bay Area, would never fall from a normal load as the 35W bridge seems to have.

The problem for Bay Area residents is that seismology is a slippery science, and old paradigms about what level of engineering is strong enough for the big one seem to change with every major event.

"We're not going to know until it happens," said Randy Rentschler, spokesman for the Metropolitan Transportation Commission and Bay Area Toll Authority, which is funding a large share of the $5.6 billion needed to rebuild the Bay Bridge's eastern span.


Advertisement

That's not to say Rentschler is pessimistic — far from it: "Caltrans has spent billions of dollars to make California bridges safe, and I think people ought to feel good about that."

And Caltrans says the bridge it has labeled as obsolete is fairly safe for its 250,000 to 300,000 crossings a day, but not necessarily safe enough to withstand a magnitude 8 quake.

After seeing images on television of the twisted steel remains of the Interstate 35W bridge in Minnesota, those nagging daily fears have been magnified. As a security guard on Treasure Island, Patrick Richard is "always on the bridge; I can't get around it."

"On a scale of 1 to 10 of a big earthquake happening right now, I think it might collapse," Richard said, adding, "but I'm not worried."

The good news for those worriers is that even one of Caltrans' biggest critics insists the old bridge, along with its permanently retrofitted cousins, the Bay Bridge western span and Golden Gate, is as tough as any in the area.

"These are 1930s bridges. They didn't have any welding almost, not in main members," as do bridges built in the 1950s and 1960s like the doomed Minnesota span, said University of California, Berkeley structural engineering professor Abolhassan Astaneh-Asl. "If you don't have welding, you don't have fatigue cracks," which, if left uninspected and unchecked, can lead to massive failures over time and are a possible suspect in Wednesday's collapse.

In addition, the eastern span also received two retrofits, one to fix the collapsed deck and get traffic moving and the second to strengthen it until its replacement is opened.

Yesterday the airwaves around the Bay Area were alive with bridge officials reassuring the motoring public that Caltrans does regular inspections and catches such signs of stress.

Ever mindful that bridges also need to satisfy drivers' psyche, Caltrans has also worked with officials to design its new structures so that people feel just as safe as the engineers believe the bridges to be.

The new eastern Bay Bridge spans, the largely assembled concrete skyway and the one-of-a-kind steel self-anchored suspension bridge that will reach 525 feet above the water, both use side-by-side decks rather than the old span's double decked design.

"It's not because we can't build a double-deck structure that's safe," said Bart Ney, spokesman for the bridge project. "It's because of the psychology of the driving public."

Ney explained that after the Loma Prieta earthquake, which crushed 42 people when the top deck of the Interstate 880 Cypress Structure collapsed onto the lower deck, as well as the 1994 Northridge quake in Los Angeles and the devastating 1995 Kobe, Japan, temblor, "people didn't want to be driving on those types of structures."

Contact Erik Nelson at enelson@angnewspapers.com or (510) 208-6410. Read his Capricious Commuter blog at http://www.ibabuzz.com/transportation.