Bay Bridge

Winning Single-Tower Suspension Design

Night view of new span looking west from Oakland

On June 24, 1998, MTC (acting as the Bay Area Toll Authority, or BATA), approved a single-tower self-anchored suspension design for the main span of the new east half of the San Francisco-Oakland Bay Bridge. The design consists of a single steel tower divided into four tapered columns, which are linked by horizontal cross-beams. Two large cables drape over the top of the tower and tie into anchorages in the roadway decks. Thinner, suspender cables hang from the large cables and connect to the outside of the roadway decks, creating "a majestic portal through which drivers pass between Oakland and San Francisco," in the words of the designers.

The array of cables creates an interesting criss-cross effect when viewed from certain angles. The back side of the span (closest to the island) is shorter than the front side, resulting in a bridge that is pleasingly asymmetrical. The asymmetry is not only visually appealing, but also shifts the tower west to a better foundation farther up the rock shelf near Yerba Buena Island, and makes possible a shipping channel with more than 1,200 feet of horizontal clearance.

This distinctive long span, which is designed to bridge the shipping channel adjacent to Yerba Buena Island, will connect to a more modest viaduct that will continue the rest of the distance to the Oakland shore. (continued below photos...)

Click on any photo to see a larger version

When it was selected in June of 1998, the incremental cost for this design (that is, the net cost above what a more basic bridge would cost) was estimated at $91 million, which translates to a 9.5 month extension of the toll surchage. In selecting this design, MTC (acting as the Bay Area Toll Authority, or BATA) also set design parameters for a bicycle/pedestrian path that would add another $50 million to the cost, for an additional 5.2 month extension of the toll surcharge.