Bay Bridge

Caltrans is still sparring with the Navy and the city of San Francisco over where the new eastern part of the SF-Oakland Bay Bridge will be located – south or north of the existing cantilever truss that is deemed highly earthquake prone. The Bay bridge consists of a western part (a pair of shortish suspension spans) over major shipping channels from San Francisco to Yerba Buena/Treasure Island mid-Bay and the Eastern part from the Island to Oakland. Yerba Buena Island is an unusual rocky outcrop and the roads go through a short doubledeck tunnel through it, and Treasure Island is an artificial extension made of dredge silt. The Bay bridge is 2x5-lanes doubledeck. One section of the east span collapsed in 1989 from the Loma Prieta earthquake and the whole bridge was out of action for two months. Subsequent investigations have shown the whole east section is vulnerable and that it is most economical to build a replacement. This will be 2x5-lanes side by side.

Caltrans first proposed a clean lined concrete box girder design for the new Eastern portion but demands for a ‘signature span’ from local political figures have led to selection of a single-tower asymmetrical suspension span. The design (above) is by TY Lin and Moffat & Nichol. Involves a four piece tower 160m (525') high located close to the shore of the island holding four main suspension cables of 0.8m diameter (32") – two shorter ones tie back into the deck on the island and two longer ones support either side of the roadway heading 385m (1263') over a shipping channel toward Oakland. It is a self-anchoring suspension span, which is an unusual bridge type anyway. This will be a first as an asymmetrical single tower self-suspender.

But the Caltrans/Lin design is far from a sure thing. Caltrans wants the new span to the immediate north of the old span. But the US Navy has a defunct base there which it is handing over to the city of San Francisco and both the Navy and the city want the bridge on the south side. There, Caltrans says it encroaches on a US Coast Guard station on the island and on the port of Oakland.

A Caltrans official told us they won’t proceed with the new span on the south side. San Francisco’s mayor Willie Brown and the navy both say they won’t allow the bridge on the north side of the bridge, so there’s an impasse. The Navy has given Caltrans permission to do drilling on the north side to explore foundation conditions for the main tower, which is a start.

Tolls collected on the Oakland side were doubled a year back to pay for the $1.5b 3.6km long project. The bridge carries 240k veh/day.