Amid talk of earlier restoration, West Seattle Bridge Task Force looks at risk management
An eye opening story on Sept. 9 by Mike Lindblom in the Seattle Times offered the potential of a much earlier return to nearly full service for the West Seattle Bridge. The story outlines how Seattle Department of Transportation engineers and consultants now believe the bridge could possibly open up to six lanes by the end of 2022. Previously SDOT has suggested repairs might extend well into 2023. The story also suggests a new lifespan for the repaired structure of between 15 to 40 years. Those decisions of course have not yet been made and await the the outcome of both the full recommendations from SDOT consultant WSP and the final decision by Mayor Jenny Durkan.
Immersed Tube Tunnel proponent Bob Ortblad, while not privy to the ongoing data from bridge monitors or relative success of repairs still maintains the bridge is unlikely to be returned to that level of service. "You can add the post-tension cabling but it's like a broken leg. It's not going to get better. Carbon fiber is brittle stuff. I think there's a 50-50 chance the bridge does not get traffic back on it. This whole thing is one big experiment. It's never been done at this scale before."
If and when a replacement is required, if a bridge is the choice in the same footprint, the community would face another likely four year closure as the old bridge is demolished (18 months) and a new one is built (2.5 years).
Ortblad pointed out again that the immersed tube tunnel option as a replacement could be pursued regardless of whether the bridge is repaired or replaced.
The West Seattle Community Task Force meeting held later on Wednesday was virtual via WebEx and offered an update on stabilization progress, an overview and Task Force feedback on the Reconnect West Seattle Final Implementation Plan, updates on the Low Bridge Access Policy, a detailed presentation on the cost/benefit analysis for the West Seattle High-Rise Bridge looking at risk management, and a facilitated Q&A with SDOT and Greg Banks of SDOT consultants WSP.
Bridge Safety Program Manager Heather Marx spoke out stabilization being done on the bridge. The work platforms that were installed in July are now moving to other spots to continue the application of the carbon fiber wrapping and epoxy injections into cracks. Holes are drilled and what amount to syringes (though larger in scale) are used to channel the super strong glue into smaller cracks.The purpose is to protect the steel inside the bridge not to make it stronger.
Post tension brackets are now inside the girders where the cabling will be attached to add linear strength.Two sets of these will be installed, one to tighten the cracked sections and later more to run the length of the span over the bridge. Carbon fiber wrap is also being applied inside the girders.
Low Bridge Access Policy
The Low Bridge Access policy was covered by Marx. Former Mayor Nickels suggested a new Van Pool policy should be established. Marx mentioned that a Task Force Committee will be established to inform allocation policies with representatives from business, employers, Metro the City and the Port. Only members of the existing Task Force would take part in this sub committee.
Reconnect West Seattle updates
Colin Drake and Danielle Friedman of SDOT led the discussion on how to get the community reconnected.
They released the final plan on Wednesday.
The SDOT initiative to move as many people as possible while the bridge is out of service moves into the next phase following the results of a multi-neighborhood survey that got more than 15,000 responses.
SDOT plans to spend $6 million over the next 18 months to implement more than 55 community projects or program elements. Drake said "We're spending a million bucks on each neighborhood."
In 2020 there are 23 community prioritized projects or actions to improve mobility and neighborhood safety.
As fall arrives 32 more will move into project development.
Drake and Friedman spoke about the implementation and community feedback and then shared the 2020 projects list one aspect of which was the establishment of a Freight Only lane northbound on West Marginal Way SW. Former Mayor Greg Nickels pointed out that this would reduce traffic capacity by roughly 50% and "will get huge pushback once this is more broadly known". Drake said they would listen to community members and stake holders before taking any action along these lines. Such a Freight Only lane would would begin at the base of the hill at Highland Park Way SW.
Jolene Haas also expressed concern about Duwamish Safe Streets not being added to the plan. Drake acknowledged that this was not in the survey process but probably should be.
The full plan was promised to be made available soon.
Cost Benefit Analysis
Marx then introduced Greg Banks who is with SDOT's engineering consultants WSP who went through a lengthy description of the Cost Benefit Analysis.
The roadmap shown above details when the decisions were made regarding the process of the Cost-Benefit Analysis. The outcome of the process is intended to make the most informed decision possible on repair or replacement.
The presentation included for the first time a more elaborate explanation of where an Immersed Tube Tunnel might be located, at least in simple terms.
Banks touched on the challenges with a tunnel from utilities, to Terminal 18 an 5 access and railway conflicts.
Banks then went into the Cost-Benefit Analysis explanation. The process consists of Attribute Weighting, then defintions of those plus measurables. Incorporating costs and how to monetize the risks involved followed by the next steps. The slides below provide that data. More information on aspects of a potential tunnel as replacement will be discussed in a meeting on Sept. 23.
All the stakeholders involved, from SDOT to the Technical Advisory Panel to the Community Task Force all agreed that seismic safety was the top concern. SDOT's Matt Donahue said that the West Seattle High Rise bridge was "probably the least vulnerable of Seattle's bridges "including the Fremont, Ballard, and Magnolia Bridges since it was the most recent built" and built at a time when seismic standards were informed by more awareness.
Also mentioned in the meeting was a request by the US Coast Guard to have an even higher clearance for a replacement bridge than the existing 140 feet. That is now part of the evaluation process.