Although the Columbia River Crossing has received the most attention, another Portland bridge project—the Willamette Crossing, a span for MAX and pedestrians north of the Ross Island Bridge and south of the Marquam Bridge—is at a more critical juncture. As Randy Gragg reported recently on the Portland Spaces Burnside Blog, TriMet and the bridge’s Boston designer, Miguel Rosales, have narrowed their search to two designs: It’s a cable stay vs. a “wave” bridge design.
Reading Randy’s interview with Rosales, posted earlier this week, it seems abundantly clear that the “wave” bridge is by far the best choice for Portland. I don’t mean it’s merely the one I like best. It’s the one practically everybody does. At the same time, that selection seems to be the underdog because of its uniqueness. It’s simply easier for engineers and bridge builders to do what they’ve done before.
Obviously the cable-stay form conjures notions of great bridges like the Golden Gate. There isn't something like it in or downtown Portland, and it's naturally dramatic. Yet, the cable-stay selection, Rosales tells Gragg, is also, somewhat surprisingly, the more off-the-shelf choice. This is a design-build process, and the contractor (perhaps the client too) favors keeping costs down as the highest priority. Building the cable-stay would allow the contractor to basically copy the other bridges of this sort. No surprises for them.
But the cost estimates making the cable-stay option may be inaccurate. The cable bridge would be longer than the wave bridge, and the longer it is, the more costly.
What’s more, the cable-stay bridge would be inappropriately tall. Rosales says its pair of 250-foot high towers would rise higher than the Marquam Bridge. (Which is very tall.) And its towers would have more environmental impact than the wave bridge because they’d be built on the shore or shallow water instead of deep water.
The designer adds of the cable option, “If the details are not done well, it can be very unattractive. Have you seen the details on the Sauvie Island Bridge for the arch? They are terrible. All the connections of the cables are very awkward. Basically, there is no finesse in any of the details. A lot of the new cable-stay bridges built through the design/build process they are terrible looking. This bridge will be design/build, [and] there is enormous pressure to cut costs.”
The wave would be the first of its kind: “Typically the undulating, parallel, steel waves providing the structural support are solid,” Gragg explains. “Rosales’ version would be an open web.” That means when you’re standing on the bridge, the outer railings would be see-through. On the cable bridge, they wouldn’t (see accompanying images).
“The cable-stay would be completely different than anything you have in Portland,” Rosales said. “But in this context, it will not look very good with the other bridges. It’s a completely different scale. It’s very monumental. The bridges next to it are kind of low key. I think it will clash. To me, a cable bridge creates the sense of a gateway into someplace. But this bridge is more a connection between the two sides of the river. It’s not really a gateway into anything. It’s about flow from one side to the other.”
Rosales and TriMet have continued to go forward on the wave design. “There have been a lot of studies done on the wave bridge because TriMet’s engineers keep asking, ‘What about this detail or that? They’re trying to figure it out,’ Rosales told Gragg. ‘We’re way into the design now. It’s more than preliminary design, very detailed. We could go farther, but everybody is keeping their distance. I don’t know what’s behind that the decision.’”
“When you do a bridge that is more unique, a lot of the details have to be figured out more carefully,” he added. “You cannot take them off the shelf. They cannot be copied from another bridge. If the preliminary design is done well and the details are resolved correctly – which would be our hope given how many hours we’ve already spent working on the wave bridge already – it’s harder to change. Engineers won’t change something that hasn’t been done before without further calculations because that’s a risk.”
“But you know, it’s not always terrible to be the first to do a design. At least three of the bridges I’ve designed were the first. They were not the cheapest of all the choices, but we kept them within the final bid amount. And they have brought a lot of attention to the places they were built. Does anybody regret them? Not at all. But did the agency take a risk? Yes.”
TriMet surely wants to do the right thing: deliver a beautiful, most functional bridge at a reasonable cost to taxpayers. There are some people focused more on cost and efficiency of construction—the short term concerns—and others looking more at the long-term value of having the right bridge by the right designer for the right place. As the transit agency’s advisory board has shown them, the wave may be the right long-term choice: a quality bridge in the tradition of the Hawthorne Bridge or the Broadway Bridge. Will they go ahead and make it, or succumb to the kind of regrettable thinking that delivered the eyesore of the Marquam? It's certainly not to say a cable bridge would be an eyesore. I'll bet we'd most all come to like it. And while it's in some ways more off-the-shelf, Morales and others could also help assure that the details and overall quality are high. But particularly as long as the Marquam is there, I'm not sure a cable bridge here, even in the best designed scenario, would be the right fit.
What do the rest of you think?