There is a strong likelihood of a large earthquake in the San Francisco Bay Area — about a 2-in-3 chance of magnitude 6.7 or larger before 2036, according to the United States Geological Survey. This New York Times piece discusses the building of the new Bay Bridge:

Unlike more conventional suspension bridges, in which parallel cables are slung over towers and anchored at both ends in rock or concrete, the 2,047-foot suspension bridge has only a single tower and a single cable that is anchored to the road deck itself, looping from the eastern end to the western end and back again. (With a conventional design it would have been extremely difficult to create an anchorage on the eastern end, in the middle of the bay.)

The new bridge is the longest self-anchored suspension bridge in the world, and it is asymmetrical, with one side of the span longer than the other. The choice of such a design raised the cost of the project significantly. In a conventional suspension bridge, the road deck is added last, hung from suspender cables attached to the main cables. In a self-anchored design, the deck has to be built first.

The eastern span replacement of the San Francisco – Oakland Bay Bridge has been under construction since 2002. Originally scheduled to open in 2007, it is now scheduled to open to traffic in 2013 at an estimated cost of $6.3 billion. A good interactive from the NYT is here. An incredibly detailed Wikipedia article is here.