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The West Seattle Bridge
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City closing in on decision to repair or replace the West Seattle Bridge

West Seattle Bridge. (Seattle DOT flickr)

We should know in just over a month whether the West Seattle Bridge will be replaced or repaired. All the risks and costs involved with the choices are now being weighed and calculated.

Why is it taking so long to figure out the West Seattle Bridge?

One of the 36 risks being evaluated is whether the Coast Guard might require a higher clearance over the Duwamish River. If that were to happen, both of the approaches would have to be altered, which would add significant costs to the project.

The City of Seattle’s Heather Marx told a task force Wednesday that it’s one of the possible variables the cost-benefit analysis must consider.

“The Coast Guard can require us to have a higher profile,” she said. “It’s not required that they do so, but that is something we have to consider a risk because they could require it of us.”

That’s the kind of detail that is going into this decision.

Seattle Department of Transportation Director Sam Zimbabwe told the group this cost-benefit analysis is only one of the factors that will be used to make final decisions. It will not determine what a repair would be, or what a replacement would be.

“We are not deciding today whether we are building a tunnel or building a replacement bridge,” he said. “We are deciding are we immediately going into replacement or are we working on repair into replace.”

The latest timelines suggest that a potential repair could give the West Seattle Bridge another 15 to 40 years of life. That’s a lot better than the initial 10 years Zimbabwe had estimated. A new bridge or tunnel would give the corridor up to 75 years of life.

An outside engineering firm is looking at three tunnel options, two north of the current bridge and one south of the bridge. The paths into the tunnel are somewhat problematic because the routes would cause problems for the Port of Seattle and other properties in the area.

“It’s hard not to believe that there aren’t fatal flaws in that whole concept,” Port Commissioner Peter Steinbrueck said.

There could be problems with moving utilities, the railroad tracks, and dredging the Duwamish River, but the city said there is no reason it can’t build a tunnel.

And again, this current analysis isn’t deciding whether a replacement would be a bridge or a tunnel — only if the city should repair first or just go to a replacement.

History of the West Seattle Bridge

The city has also released a list of 23 projects that are ready to go to help with traffic mitigation because of the West Seattle Bridge closure, including small improvements like better striping, traffic calming devices, and signal timing changes.

Former Seattle Mayor Greg Nickels, who co-chairs the task force working on the West Seattle Bridge, said one of the options on the table is a non-starter for him. That has him opposing a strategy that would create a northbound freight-only lane on West Marginal Way, which could cut capacity to the public by nearly 50%.

“When the community is struggling to find capacity, to keep from having people diverting into our neighborhoods, I think reducing the capacity on West Marginal Way northbound just sends the wrong message, and I think you will get huge push back on that when it becomes more broadly known,” he said.

The city said these 23 projects aren’t set in stone yet, and neither are the 32 others they are exploring. If they don’t work with what the neighborhoods want, they could be changed.

The city also plans to add “your speed is” signs on Airport Way and Cloverdale to try and reduce speeding on those two streets.

The task force is still figuring out who can use the Lower Spokane Street Bridge and what the upcoming photo enforcement on the bridge will look like. We’ll find out more in two weeks.

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