Existing Dumbarton Rail Bridge

The existing Dumbarton Rail Bridge will see revived rail service within a few years. A new bridge for
high speed rail would replace it if the Altamont Alignment is chosen.


Bay Crossing



The Altamont Alignment requires a new bay crossing at Dumbarton, between Newark and East Palo Alto. This is the location of the first bridge across San Francisco Bay, the Southern Pacific's Dumbarton Bridge, built in 1910. The old bridge is owned by the San Mateo County Transporation Authority. It will soon see a revival of passenger rail service, with new commmute trains running between BART in Union City and destinations on the Caltrain line.

If high speed rail comes into the Bay Area across the Altamont Pass, it would cross the bay at Dumbarton on a new, high-level bridge, replacing the old rail bridge. A new rail bridge in this location would be a simple project, costing about $200 million. But there is a misconception that a bridge here would be impossible to build......

No new bridge has been built across the bay in my lifetime.... CHSRA staff to MTC, May 9, 2003

Let's take a look at this statement. Without knowing the exact age of the staff member, we'll assume he was born sometime after the Bay and Golden Gate Bridges opened in the 1930's.

From Caltrans' site on Bay Area Toll Bridges:

In 1956, the Richmond San Rafael Bridge opened.

In 1958, the second Carquinez Bridge opened.

In 1962, the Benicia Bridge opened.

In 1967, a new San Mateo Bridge replaced the original span.

In 1984, a new Dumbarton Bridge replaced the original span.

In 2003, a second trestle was added to the San Mateo Bridge.

In 2003, a new Carquinez Bridge replaced the original span.

From my count, 7 bridges have been built across the bay in the past 50 years.

A new bridge would cost billions.... CHSRA staff to Atwater City Council, October 16, 2003

A new Dumbarton rail bridge will cost no more than $200 million. The 6-lane highway bridge built at Dumbarton in 1984 cost $70 million. Using Caltrans' Construction Cost Index to escalate the 1984 cost to 2004 dollars,

Caltrans Construction Cost Index

which sat at about 95 in 1984, and sits at 190 today (from Caltrans), the index has doubled. This means that what cost $70m in 1984 would cost about $140m today. Allowing for an extreme variation in costs due to added environmental safegards and mitigations today relative to 1984, and ignoring that the 1984 highway bridge is 2.5 times the width of a high speed railway bridge, it is safe to assume that $200m should be sufficent to build a new rail bridge at Dumbarton.

...look how complex the Bay Bridge project is.... CHSRA staff to MTC, May 9, 2003

The new East Span for the Bay Bridge, is going to be 10 lanes (120') plus shoulders (32'+/-) and walkways (24'+/-) or about 176' wide on twin roadways. The cross-section for a twin track HSR bridge is about 37', or less than 1/4 the width of the Bay Bridge. Each bridge is roughly 10,000' long. Since costs are calculated by size and complexity, the Dumbarton Bridge would be less than 1/10 the cost, or less, of the East Span because:

  • It's 1/4 as wide.
  • The East Span of the Bay Bridge (ESBB) provides a clearance 191' high and 1,400' wide over the main channel - The Dumbarton highway bridge (would be same for a high-level rail bridge) only needs to provide a clearance over the main channel of 85' and a span of 340'. That is less than 1/2 the height of the ESBB and less than 1/4 the horizontal clearance.
  • It doesn't need to build expensive bypasses to keep existing traffic moving (check out the plans for temporary structures to connect the new bridge to Yerba Buena Island).
  • It doesn't have an un-tested "self-anchoring" suspension system, adding much to the cost.
  • It crosses much shallower water (easier foundations)
  • It doesn't cross an extremely active channel, nor is it next to ship traffic of the Port of Oakland.

Existing Dumbarton SR84 Bridge


More discussion of the Bay Bridge project versus a new Dumbarton railway bridge..........

Discussion of wetlands impacts in the South Bay and Central Valley..... 


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