Losing the West Seattle Bridge

The closed West Seattle high bridge (image: SounderBruce)

On Wednesday, SDOT revealed bad news about the deteriorating West Seattle Bridge. The bridge now seems certain to remain closed through the end of 2021. It is not clear whether it can ever reopen to traffic. Any repairs are unlikely to yield more than another ten years of useful life. (The coverage of the technical issues by SCC Insight is recommended).

Long after the COVID crisis has receded, it will have a disastrous impact on mobility within West Seattle and to downtown. The bridge normally carries 100,000 cars and 25,000 transit riders daily.

West Seattle will need a new road bridge no later than about the time Link light rail to West Seattle is scheduled to open. So while Seattle absorbs the budgetary impact of repairing and replacing its busiest arterial bridge, and West Seattle residents look forward to years of grinding traffic congestion, there may also be an opportunity to combine these projects and reduce the total cost of the new bridges across the Duwamish.

Link to West Seattle is scheduled to open in 2030, initially with a stub line terminating at SODO, followed by through-service to the downtown tunnel in 2035. The timeline should be viewed as aggressive, with controversy over the alignment already having delayed the EIS alternatives selection. Local demands for tunneling within West Seattle threaten to add maybe $700 million to costs and require third-party funding. At the same time, the COVID crisis threatens delays to ST3 projects as tax revenues come up short of expectations.

All of the options being studied for the Duwamish rail crossing are close to the existing road bridge (image: Sound Transit)

Combining two complex bridge projects may not be a recipe for accelerating timelines. But it may eventually reduce construction costs if a single structure is determined to be less expensive than two, which would be a boon for Sound Transit and Seattle.

First, SDOT must figure out its timeline for construction. It's not yet known whether the bridge can be repaired for about ten more years of useful life, or if a more urgent bridge replacement is needed. The current bridge opened just six years after its predecessor was struck by a freighter and irreparably damaged. In our more cautious era, Sound Transit is targeting a final design for West Seattle Link in 2025 with five years of construction to follow.

Whether and when the high bridge can be repaired may determine whether SDOT and Sound Transit can collaborate on a shared bridge. It gets more complicated if one agency needs to move more quickly than the other. We should learn more about that assessment in the next few months. Whatever structures are eventually built, it makes sense for Seattle and Sound Transit to coordinate activities as separate bridges would nevertheless be close to each other. Close coordination may yield an outcome with reduced property impacts. But, as Mayor Durkan observed Wednesday, the city will not want to lose time.

The construction of the high bridge in 1984 cost about $400 million in current dollars. The budget would surely be higher today (although perhaps a new bridge need not be as high). At a minimum, the city will want to design a safer replacement of the current lanes with shoulder space. The fourth eastbound lane was not part of the original design, and the extra load may have contributed to the bridge's cracking. If the city adds HOV lanes across the span in both directions, the cost will rise further, but may be worth it. A rebuilt bridge with complete HOV lanes would be a boon for buses until rail opens.