The Bay Bridge tunnel through Yerba Buena Island is showing signs of crumbling.
Nine days ago a two-foot chunk of concrete fell in front of a car in the eastbound lanes, causing a blowout and minor damage. A report now said the 80-year-old tunnel is showing signs that some of its steel reinforcements are corroding.
"It's a major concern," said Lisa Fulton, a metallurgical engineer. "It's a safety hazard and that's exactly what happened."
Fulton said the cause is water seeping into the tunnel, and over time permeating the concrete and rusting the steel reinforcements.
"The things about this type of damage is you can't see how deep it is because you only see superficially," Fulton said, adding the rusting could extend deep within the tunnel. "If you have a steel beam there, the water can cause corrosion."
Caltrans said investigators are looking into the issue.
"What we have to find out is this internal or external? Was this caused by an internal structure problem? Wait it hit by an oversized vehicle? Was it some combination of both?" Caltrans spokesman Bob Haus said.
Caltrans also does not want to rule anything out regarding the cause, an answer that left Fulton shaking her head.
"This is not damage from any vehicle, or any other thing," Fulton said. "This is definitely deterioration."
Caltrans will not speculate how long it might take to repair the damage and said it first must determine the cause and the extent of the problem.
Haus said if Caltrans must close lanes to make repair it will try not to do it during commute times. Officials said more than a quarter-million people cross the Bay Bridge every day.