San Francisco – Oakland Bay Bridge Second Crossing

Structural Forum is intended to stimulate thoughtful dialogue and debate among structural engineers and other participants in the design and construction process. Any opinions expressed in Structural Forum are those of the author(s) and do not necessarily reflect the views of NCSEA, CASE, SEI, C3Ink, or the STRUCTURE® magazine Editorial Board.

The Bay Bridge is one of the grandest engineering achievements in American history, as described in the Feature article this month. However, the recent renovation has not added a single lane to relieve traffic congestion, which has a negative impact on the Bay Area and California economies. There is one obvious solution for the problem – to build a second crossing between San Francisco and Oakland on an alignment approximately parallel to the original bridge.

After initially proposing this idea, the authors completed a feasibility study. We believe that the new bridge should be a double-decker, saving 15% of the cost versus two side-by-side decks and saving 50% of the shade cast on the Bay. The west span should be a new suspension bridge in harmony with the existing, with complementary spans up to 2500 feet (760 m); the east span can be a new bridge with spans similar to the existing east portion, but it would be more efficient to retrofit and relocate the existing structures onto new foundations on piles near the current alignment.

Figure 1

Existing Bay Bridge and proposed second crossing.

The old existing structure is currently planned for demolition. Saving and reusing it is only one option for building this portion of the second crossing, but it seems to be the best. The existing east span foundations are the most deficient part of the old bridge, while its superstructure has performed well during the past 80 years of service. Our study makes use of effective methods of strengthening the existing trusses, such as transforming the system to several continuous structures, reinforcing or replacing some elements found deficient, replacing the existing concrete deck with orthotropic or other lightweight steel decks, etc. Such reuse is a rare opportunity to create the much-needed second trans-bay crossing faster and for less cost.

The feasibility study proves that a new Second SFO Bay Bridge Crossing is perfectly achievable. The new west span – as a suspension or cable-stayed bridge of up to 2500 feet (760 m) – is not a problem for today’s construction techniques. Currently there are more than 40 such bridges with spans longer than 2500 feet. Based on our study, the new east span could be easily built with modern steel trusses and orthotropic or other lightweight decks, or by relocating the existing structures to new foundations using high-capacity jacks on barges with temporary piers. Preserving and reusing 60,600 tons (55,000 metric tons) of steel is also a significant economic and environmental saving.

The main achievements of the new crossing would be increasing the trans-bay traffic capacity and providing a bicycle lane between San Francisco and Oakland. It would add four new lanes to the existing five in each direction, thus increasing the overall capacity by 80%. By 2035, the Bay Area population is estimated to increase by 50% from 1990, when the traffic congestion was already very heavy. The California Department of Transportation (Caltrans) needed five years of planning and design plus nearly 12 years of construction to build just one half of a full crossing, so it is obvious that we are running out of time to solve the problem.

The estimated steel quantities for the second crossing are 152,670 tons (138,500 metric tons), including over 99,200 tons (90,000 metric tons) for new structures and 53,460 tons (48,500 metric tons) for retrofitted members from the old east span; 78,800 tons (71,500 metric tons) for the new west crossing (including the San Francisco approach and Yerba Buena Island transition structures), and 73,850 tons (67,000 metric tons) for the east crossing, only 20,400 tons (18,500 metric tons) of which would be new steel. This project can be completed in less than five years, including design competitions and construction. Based on recent construction of similar bridges, the estimated cost is $2.55B. The efficiency of the second bridge crossing is demonstrated by comparing the 152,670 tons for this entirely steel structure with the 266,750 tons (242,000 metric tons) of steel used for the new east crossing replacement, which is about half as long as the overall new proposed crossing and mainly a concrete bridge.

Accomplishing a second Bay Bridge crossing is a challenging task, but not at all comparable to the problems that our predecessors had to overcome some 80 years ago, designing and building simultaneously the Bay Bridge and the Golden Gate Bridge during the Great Depression. This project is completely within the capability of American engineers and builders; the only challenge is to persuade federal and California state transportation authorities to begin working immediately on planning and designing the new crossing.

The advantages of the second Bay Bridge crossing are:

  • Solving the traffic congestion on the current bridge;
  • Using the most innovative techniques available to build a new crossing within reasonable time and cost;
  • Providing an additional transportation link at considerable materials and cost savings;
  • Completing the pedestrian/bicycle lane for the full length between Oakland and San Francisco;
  • Setting an example for efficient use of funding for infrastructure renovation; and,
  • A great opportunity for our engineers and builders to revive the art of American bridge engineering.▪

A similar article appeared in the IABSE Conference Rotterdam Report, May 2013.

Letter to the Editor

As a life-long San Francisco Bay Area resident, I was motivated to write this letter when I read the two articles published in the February 2014 issue regarding the San Francisco-Oakland Bay Bridge. I found the articles topical and provocative. However, if we are to improve rush hour traffic through the San Francisco-Oakland-Berkeley corridor by considering the addition of a second identically configured parallel bridge adjacent to the existing one, I would have liked to have seen some of the more obvious questions/issues addressed:

  • Can the existing freeways at either end of the proposed second and existing bridges handle the greater number of vehicles on the two bridges so that the overall traffic situation would be improved?
  • What would be the cost of the new surface roadways, connector ramps and access points, and perhaps new freeways required to join to the new bridge? Where would these roadways be located and what would be the environmental impact (traffic, business, noise, views, etc.) on the cities of San Francisco, Oakland and Berkeley?
  • Assuming that the original 1930s bridge design was ideal, what would be the engineering and cost rationale for building a new bridge with re-used, archaic 1930s members, rather than just using new materials with an improved double deck configuration? Is it necessary to replicate the clear span of the Eastern span cantilever section?
  • Would it be practical and cost-effective to dismantle the existing bridge in such a manner as not to damage the individual elements, so that they could be stored and reconstructed later?
  • Since the original Eastern span is widely considered unattractive and a long-standing insult to the residents of the East Bay, would it be possible to get public support for its reconstruction?

I agree that the new Eastern span has not made the vehicular traffic situation any better; it actually seems worse now, if that is possible, and it is likely to get even worse in the future. But since the new Eastern span has just opened after 25 years of design and construction and at a huge cost to the taxpayers, not to mention the question of whether it was an appropriate or efficient engineering design, I must admit that adding another bridge in essentially the same place did not cross my mind. I have not really recovered from the last project. Besides, the concept of adding another cross-bay bridge south of San Francisco to the East Bay, also known as the “Southern Crossing,” has been studied in various alignments and locations since the 1940s, but consistently rejected.

As an alternative to more bridges and roadways, increasing the capacity and service area of the BART rail system deserves serious consideration as a means of reducing the demand on the existing Bay Bridge. Maybe a Southern Crossing with shared vehicular and BART rail traffic could be part of a comprehensive traffic improvement plan. Some people like to ride ferries, but I think that the time for that technology, as a serious contributor to traffic capacity, is in the past, although it might play a small part in the future.

Before we consider a second Bay Bridge, we really need an in-depth study to flush out the best alternatives and the true costs.

John Dal Pino, S.E.

P.S. Saving the old Eastern span is really a moot point, since demolition is already underway.

 

Response to John Dal Pino’s “Letter to the Editor”

These are all good points. We share the concerns raised by Mr. Dal Pino, and assume that various transportation agencies share them, too

The combined factors of high costs and lengthy construction time devoted to replacing the east span have likely exhausted any public enthusiasm for an additional bridge. Even so, substantial increases in public transportation budgets will not provide adequate relief where it is most needed. A second underwater tube for BART, for instance, is unlikely to address the true nature of the congestion. The only viable solution is a second bridge.

We believe the challenges associated with a second crossing can be surmounted. While space does not allow us to expand on our ideas for why a parallel bridge has practical and economic advantages, we also readily acknowledge the potential for other viable bridge options. Ultimately, we believe that a multi-stage design competition would get the best ideas on the table.

Regardless of aesthetic preferences related to structural systems (steel truss vs. concrete viaduct), the fundamental question remains: “How long do we delay plans for an additional crossing, and at what ultimate cost?” We feel engineering professionals are better suited to tackling this question pro-actively, rather than waiting for it to make the agenda of elected officials.

Ronald F. Middlebrook, S.E. and Roumen V. Mladjov, S.E.

About the author  ⁄ Ronald F. Middlebrook, S.E.

Ronald F. Middlebrook, S.E. (ronfranco@gmail.com), is retired from Middlebrook + Louie in San Francisco, California, and is a Past President of the Structural Engineers Association of Northern California (SEAONC).

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