From SFWiki

The Bay Bridge crosses the San Francisco Bay from the East side of the peninsula over to Berkeley and Oakland. It is a bridge in two parts, separated in the middle by Treasure Island. The Western span is a suspension bridge, while the Eastern span is a piece-meal metal bridge which is in the process of being replaced, due to its lack of Seismic Retrofitting.

There is a toll at the Eastern entrance to the bridge, which is currently priced at three dollars.