Debate continues over new I-5 bridge design

Cost, esthetic appeal, and impact on existing buildings, roads and airports are all factors in choosing a design for the new I-5 bridge, scheduled to start construction (pending funding) in 2012 or 2013.

Last year, the Columbia River Crossing taskforce, a joint effort between Washington’s and Oregon’s Departments of Transportation (DOT), recommended an “open-web” design for the new bridge. Early last month however, the Columbia River Crossing Bridge Review Panel nixed the feasibility of that design. According to the panel’s report, the open-web design posed too many engineering challenges. The 16-member panel suggested three alternative designs:

·    Composite deck truss bridge: Basically a flat-bed design, similar in appearance to a cross between the I-205 bridge and the rejected open-web design.

·    Cable-stayed bridge: Consists of one or more towers, with fan- or harp-shaped cables supporting the bridge deck. The Ed Hendler Bridge, which spans the Columbia River between Pasco and Kennewick on State Route 397 was the second cable-stayed bridge constructed in the United States (1978).

·    Tied-arch bridge: Outward-directed horizontal forces of the arch are borne as tension by either tie-rods or the bridge deck itself, rather than by the ground or the bridge foundations. Portland’s Fremont Bridge is the second-longest tied-arch bridge in the world.

Last week, the Washington and Oregon Departments of Transportation considered the merits of each design and released a draft recommendation in favor of a composite deck truss bridge. The DOTs concluded that a deck truss is the only bridge that meets all the criteria identified by the governors.

“The deck truss bridge allows us to take advantage of all the work done to date and move forward quickly,” said Washington Transportation Secretary Paula Hammond.

The DOTs now seek public review and comment on their draft recommendation before making a final recommendation to the governors in about two weeks. Before a final recommendation occurs, engineers will continue to weigh many factors including, airspace of nearby airports, marine traffic clearance requirements, navigation channel locations, fluctuating river levels, existing infrastructure and the inherent limitations of each design.

For instance, according to the bridge-design Web site bridgepros.com, cable-stayed bridges are price competitive in the 500- to 2000-foot span length range. The current I-5 bridge is closer to 3,500 feet long. Long-span cable stayed bridges can be vulnerable to high winds, which could be an issue given the proximity of Columbia Gorge.

Infrastructure considerations

According to Vancouver Mayor Tim Leavitt, both the cable-stayed and tied-arch designs would require a straighter path across the river than the current bridge, which could negatively impact existing buildings, such as the West Coast Bank Building. The composite truss design could accommodate more of a curve, allowing it to more easily integrate with the existing infrastructure on both sides of the river.

While the owners of the West Coast Bank Building may be somewhat concerned, properties farther away have less to be worried about.

“We’re far enough up the corridor that none of the connector alternates would have much impact on the Historic Site,” said Elson Strahan, president and CEO of the Fort Vancouver National Trust.

Another consideration is how the bridge design could affect air traffic. None of the three designs interfere with PDX traffic, but the cable-stayed design is tall enough that approval of the design would require a waiver from the Federal Aviation Administration (FAA).

For this reason, Steve Horenstein, a business and real estate attorney with Miller Nash LLP (located in the afore-mentioned West Coast Bank Building), thinks the DOTs and governors will choose the composite truss deck design. Horenstein also serves as co-chair of the Project Sponsors Council, which advises the governors on issues related to the River Crossing project.

“The truss deck design costs the least and has more certainty, because it doesn’t need FAA approval,” said Horenstein.

Leavitt, however, points out that the existing 230-foot towers on the I-5 bridges intrude into Pearson’s airspace already, while the proposed cables would actually improve the situation.

“It seems counter-intuitive that the FAA still needs to weigh in,” said Leavitt.

Cost considerations           

According to the Columbia River Crossing Bridge Review Panel’s recent report, the composite deck truss design would save nearly $100 million over the old open-web design. The other two alternative designs would also save money, but not as much. The cable-stayed design would be about $40 million cheaper than the original design, and the tied-arch design would only save about $10 million.

But it is important to remember that the bridge represents only about one-quarter of the total Columbia River Crossing project, which stretches for five miles from Marine Drive in Portland, north to SR-500.

Esthetic and community considerations        

While local officials admit that cost and infrastructure impact are important, they are also concerned about how the bridge project will affect the community.

“It’s absolutely incumbent on Vancouver to be crystal-clear as to how our community is left when the last bit of asphalt is laid down,” said Strahan. “Will our children feel we were good stewards of the community’s quality of life?”

Leavitt agreed, adding, “The City Council expressed a preference for a structure that will reflect the values of the community, and have some sort of esthetic value.”

Perhaps, suggested Leavitt, some sort of compromise between practicalities and esthetics is possible. If the composite deck truss design is chosen, said Leavitt, “that doesn’t preclude some vertical enhancement” that was appealing to the eye and could contribute to regional pride in the project.

I-5 Bridge Timeline

1917: First span opens 5 cent toll replaces steam ferry service in place since 1870

Cost: $941,000

1958: Second span opens 20 cent toll for cars, 60 cent toll for trucks

Cost: $14.5 million

2002: Bi-state task force formed to identify and prioritize I-5 corridor bottlenecks. The Interstate Bridge is one of them.

2008: New bi-state task force forms to propose bridge and infrastructure design.

2010: “Open-web” design is recommended by Columbia River Crossing task force, design is reviewed by an independent review panel.

2011: Independent review panel rejects feasibility of open-web design and recommends three alternative designs. The Washington and Oregon Departments of Transportation release a draft recommendation of the deck truss design. The DOTs now seek public review and comment on that recommendation before making their final recommendation to thegovernors in mid-March.

 

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