San Fran Bay Bridge New East Span
By Peter Samuel
San Fran Bay Bridge
New East Span total $1.5 billion
One of the world's most heavily trafficked toll bridges is to be mostly rebuilt in a $1.5b+ project. California's governor Pete Wilson announced Feb 13 that the state had accepted a recommendation from the state dept of transp (Caltrans) and a panel of seismic experts that the eastern span of the San Francisco-Oakland Bay Bridge be completely replaced rather than beefed up to protect it against future earthquakes. The bridge which carries an average 280,000 vehicles/day is a double deck structure 5 lanes on top of another 5 lanes. Built by a state Toll Bridge Authority it opened in 1936 with the upper deck carrying 6 lanes of car traffic and the lower deck carrying trucks, buses and a pair of train tracks. In the late 1950s the crossing was reconfigured under Caltrans to 5-atop-5 lanes and the BART subway system took trains into an under-Bay tunnel.
The Bay Bridge takes a lot of the commuter traffic of four major east Bay freeways (I-80, SR-24, I-580 and I-880) and local traffic from the major railhead and port city of Oakland to the southern part of the San Francisco central business district where it connects to the I-280 and US-101 expwys. The Bay Bridge is a total of 7.2km shore-to-shore and is strictly a bridge/tunnel/bridge. The west span of 2822m links San Francisco to the small but high mid-Bay island called Yerba Buena and has two suspension spans. The island of shale rock is traversed in large part by a 546m long double deck tunnel claimed to be the largest cross-section tunnel in the world (23m wide 18m high).
The East Span between the island and the East Bay shore near Oakland is a 3200m long bridge of a series of steel cantilever truss spans, the longest of which (425m) goes above an old shipping channel to the port of Oakland. It is said to have consumer 6% of total US steel production in 1933 with trains from Pittsburgh running constantly to Oakland with the rolled sections. This East Span is in the worst shape. During the 7.1 Richter scale Loma Prieta earthquake of 1989 the bolts on the upper deck of a truss section sheered off and that deck section hinged down onto the lower deck closing the bridge for several weeks. Investigations have found several of the main piers are weakened. Most are on wooden deep piles which are rotting.
Retrofit vs New Span: An optional retrofit of the existing structure would involve two completely new piers to support the long truss span midway and substantial reconstruction of the existing piers and other strengthening for an estimated cost of $900m. For only about $100m more (plus $75m for interim strengthening and demolition of the old span) the proposed new East Span Bridge can be built. It will be located curving north of the existing structure, a pair of 5-lane bridges side-by-side. Equipped with breakdown shoulders, a gentler grade and eliminating a sharp turn at the eastern end of Yerba Buena Island the new bridge will speed traffic flow slightly and reduce congestion caused by disabled vehicles. The new travel lanes will be 12' compared to the present 11' (3.66m vs 3.35m). Caltrans favors a clean lined thin concrete box girder structure 3075m long consisting of two 168m spans and eighteen 152m spans, though it has presented a double tower cable stayed main span option that would cost an extra $220m. The state says that if Bay area communities want the fancier cable-stay design, they will have to pay the premium themselves. It doesn't serve any practical function.
The West Span Bridge is to be given a seismic retrofit costing almost $400m, so the total Bay Bridge upgrade will cost in the region $1.5b to $1.8b. Caltrans hopes for completion in 2004. Tolls will almost certainly double on the present low $1 though a substantial amount of tax money is proposed for the project. (Contact Jeff Weiss 510 286 5543 www.ca.dot.gov)