By Henry Fountain

SAN FRANCISCO — Venture deep inside the new skyway of the San Francisco-Oakland Bay Bridge, and it becomes clear that the bridge’s engineers have planned for the long term.

At intervals inside the elevated roadway’s box girders — which have the closed-in feel of a submarine, if a submarine were made of concrete — are anchor blocks, called deadmen, cast into the structure. They are meant to be used decades from now, perhaps in the next century, when in their old age the concrete girders will start to sag. By running cables from deadman to deadman and tightening them, workers will be able to restore the girders to their original alignment.

The deadmen are one sign that the new eastern span of the Bay Bridge, which includes the skyway and a unique suspension bridge, is meant to last at least 150 years after its expected opening in 2013. (The existing eastern bridge, which is still in use, will then be torn down.)

But to make it to the 22nd century, the new span may at some point have to survive a major earthquake, like the one that destroyed much of San Francisco in 1906 or the one that partly severed the Bay Bridge in 1989. With two faults nearby that are capable of producing such large quakes, survival is no simple matter.