Choosing what kind of bridge will span the Columbia River between Vancouver and Portland is an important decision that will last for a century or two. Beyond a shadow of doubt, the best choice is a cable-stayed bridge. Not because it will look better, but because it will function better for the people on it, the fish beneath it, and for the tax- and toll-payers footing the bill.
The Washington and Oregon departments of transportation have recommended a “composite deck-truss” similar to the Marquam Bridge over the Willamette River. Supposedly, it will cost $50 million less and be less risky to build, while the cable-stayed option is depicted as an aesthetic luxury. While it is certainly true that the cable-stayed would offer a landmark connection between our cities and states, the reasons supporting the cable-stayed are all practical.
The cable-stayed bridge is likely more fish-friendly. With its longer spans, it requires only three piers, all of which would be built in the deepest part of the river, farther from critical habitat near the river’s shoreline. The deck-truss design demands at least 10 piers and likely 12, many of which will land near or in the highest-value, shallow habitat.
Though a deck-truss bridge certainly can be built to our seismic zone standards, nobody knows for certain just how devastating our long-overdue Doomsday Event will be. From Loma Prieta, Calif., in 1989 (which caused a section of the Oakland Bay Bridge to fail), to Santiago, Chile, in 2010, to New Zealand and Japan just this year, each major earthquake teaches engineers new lessons. But with its inherent flexibility, bridge design experts conclude that a cable-stayed bridge is far better equipped to survive nature’s surprises.