From most vantage points in the San Francisco Bay, two bridges compete for attention.

The Golden Gate is the region's brand ambassador. It draws tourists, aesthetes, and those interested in driving over an architectural apotheosis. The Bay Bridge, on the other hand, is the region's transportation workhorse—and these days, it's getting a lot more attention than its orange neighbor, thanks to several hundred rusted-out anchor bolts and one recently exposed corrosion-threatened main cable.

Opened in 2013, the Bay Bridge's new eastern span cost $6.4 billion, and its failures are attracting the ire of the region's taxpayers, legal experts, and those interested in driving over a piece of public works that will survive the next major earthquake and fifty to one hundred years of normal wear and tear. As architecture writer Jay Merrick once wrote: "Engineering is interesting when it works, but much more compelling when it doesn't."

So what's behind the compelling failures of the Bay Bridge? No bridge is purposefully engineered to invite rust. But onlookers don't have to shrug and blame Murphy's Law while they wait for investigations, more investigations, and (probably) lawsuits sort out the blame. "There are generally two different causes for a structure's problems," says Edward Tenner, author of Why Things Bite Back and several other books about engineering and failure. "One is when something just isn't built or maintained according to best practices, and type two is when there was an innovation that wasn't fully tested in the field."

It's typically easier to pull out the mistakes in the first category—the neglect of best practices. The Bay Bridge is really two bridges that meet halfway on an island in the middle of the San Francisco Bay; the half we care about is that recently rebuilt eastern span. On Monday, the San Francisco Chronicle detailed how rainwater is running into the anchorages for eastern span's main steel cable. Every day, 240,000 drivers rely on that potentially rusted cable.

That influx of water is possible because construction workers left the anchorages open to the elements for a year during building, despite instructions that they be sealed. But that's not all. After massive, floating cranes raised the bridge's sections and attached them to the cable, workers installed guard rails. Unfortunately, the holes they drilled let rainwater flow into the anchorages.

Another example of best practices failing are the hundreds of rusted seismic anchor bolts in the bridge tower's foundation. A state senate investigation revealed that these bolts—made with shoddy steel—weren't properly tested. But the bolts were part of a design approved by the state's transportation agency, procured by a third party contractor from a manufacturer in China, and tested by a third party lab before installation. "Engineers need to specify the right materials, and somebody needs to test them," says Raymond Levitt, a civil engineer at Stanford University. "Somewhere in that chain the ball got dropped."

CALIFORNIA DEPARTMENT OF TRANSPORTATION

These problems go back to the Bay Bridge's innovative (and really quite beautiful) design. In other words, the type two failure mentioned above. The bridge's asymmetrical eastern span is supposed to evoke the Golden Gate's suspension apparatus: One side of the cable is a long, quadratic curve and the other a steep Gaussian swoop. But unlike the Golden Gate's cables—which are anchored into firm basalt—the cable holding up Bay Bridge's eastern span is looped through, and connected back to, the bridge itself. In other words, the east span is self-anchored, bootstrapped just like so many precocious young companies whose employees drive over the bridge every day to work.

So it's not really fair to compare the two bridges when it comes to their engineering specs. "When the Golden Gate Bridge was built, that was using proven technology," says Tenner. The Bay Bridge's design has much more to prove.

Especially when it comes to its self-anchored suspension. Technically, that design is proven, too: Pittsburgh's Three Sisters Bridges were built using the technology in the 1920s, and South Korea's Yeongjong Bridge is a self-anchored span longer than 900 feet. But those bridges all share their loads over two towers, and the Bay Bridge is over 1,200 feet long, asymmetrically loaded on a single huge tower. The Bay Bridge might be too ambitious. "It’s not beyond human capacity or knowledge to do a bridge like this right," says Levitt. "But I think there are more problems than I would expect to see on a bridge this complicated."

In his 2012 book To Forgive Design: Understanding Failure, Henry Patroski, a scholar of disaster, wrote that engineering innovations have cycles. Once an engineer establishes a new design, others push it for bolder designs. "But if it gets bold enough it runs into new or unforeseen events that reveal weaknesses," Tenner explains. “For example, now we have bigger and bigger cable stay bridges, and it’s not clear if there might be some hidden problem with cable stayed bridges that might be revealed over time."

The Bay Bridge's problems are still coming to light, but none so far are terminal. This is lucky. Plenty of engineering projects discovered their problems too late. For every Golden Gate, there's a Tacoma Narrows, a bridge designed by the Golden Gate's designer, and just as beautiful—at least until it got shook down by the wind. At this point, the only things shaking down the Bay Bridge are hordes of taxpayers, commuters, inspectors, and journalists.