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TRANSACTIONS NEWSLETTER ONLINE

November-December 2009

Project Update
Next in Line for Seismic Retrofits:
Dumbarton and Antioch Bridges

Dumbarton Bridge (top); Antioch Bridge (bottom).
Photos: John Huseby, Caltrans

The Dumbarton and Antioch bridges may not have the iconic presence, name recognition or heavy traffic volumes of the San Francisco-Oakland Bay Bridge, but they are important links in the regional transportation network nonetheless. And now MTC’s Bay Area Toll Authority (BATA) is working with Caltrans to bring these spans up to current earthquake safety standards. BATA is also developing a plan to raise tolls on the region’s state-owned bridges to cover the $750 million cost of the retrofits as well as to compensate for declining toll revenues and escalating construction bond costs.

“These two bridges were built before the Northridge and Loma Prieta earthquakes,” said Andrew Fremier, the MTC deputy executive director who oversees BATA’s operations. “We’ve learned a lot since then.”

Opened in 1982 and 1978 respectively, the Dumbarton and Antioch bridges were too young to merit a seismic review back in the 1990s when Caltrans initially mapped out a bridge seismic retrofit program. That earlier effort targeted five of the region’s seven state-owned toll bridges and is now largely complete, with the exception of the new East Span of the Bay Bridge, which is still under construction.

The 1.6-mile long Dumbarton Bridge carries an average of 60,000 vehicles a day across the southern end of the Bay. The retrofit strategy calls for modifying deck joints and reinforcing columns on the approaches. Along the bridge’s central hump, new isolation bearings will be placed between the superstructure and the piers to reduce shaking movements transferred to the deck in the event of an earthquake.

The retrofit approach is similar for the Antioch Bridge, which stretches 1.8 miles across the San Joaquin River and transports an average of 15,000 vehicles a day between Eastern Contra Costa County and Sacramento County. Its tall columns also will require cross-bracing.

The retrofit work is scheduled to begin by April 2010 and be completed in 2012 on the Antioch Bridge, and 2013 on the Dumbarton Bridge.

— Brenda Kahn

Toll Increases Ahead

MTC’s Bay Area Toll Authority has been formulating scenarios for raising the current toll scheme for the region’s state-owned bridges, under which cars and light trucks pay $4, trucks pay according to the number of axles, and carpools and vanpools traverse for free during commute hours. View and comment on current proposals.

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