Now that an initial structural analysis of the West Seattle High-Rise Bridge is complete, city officials must do a cost-benefit analysis on whether to repair the bridge, or replace it with a new one.
Officials said that engineers, bridge consultants and the city’s technical advisory panel all agree that repairing the bridge is possible. However, the question now remains, city officials said, whether the cost to repair the nearly 40-year-old bridge will be a good investment of taxpayer money, over the cost of replace the bridge.
The bridge, which connects West Seattle with the rest of the city, was closed in March after cracks were discovered in the bridge’s underside which appeared to be growing quickly. SDOT has since said it anticipated the bridge would remain closed until 2022.
At issue now is whether or not repairs would produce a bridge that would last another 15 years, or whether the cost of a new bridge would be a better investment.
“Our bridge consultants at WSP have been working on the engineering contours of a cost-benefit analysis for quite some time, so we are already several months into this work,” SDOT said on its web site. “This has resulted in the identification of a variety of broad concepts for what repair or replace could look like and a clear set of choices to be evaluated and compared through a cost-benefit framework. These are by no means complete designs, but serve as a starting point for weighing the pros and cons for these potential pathways forward.”
While the city does its cost-benefit analysis, it is simultaneously searching for a team to lead the design and engineering for a potential placement.
The city and its Task Force teams will be looking at six broad concepts — shoring up the bridge to restore some travel capacity; more comprehensive repairs to restore traffic capacity; partially replacing the superstructure with foundation strengthening; replacing the entire superstructure with foundation strengthening; replacing the entire bridge in the same footprint; or replacing the entire structure with a tunnel.
Officials will look at 10 criteria when judging the cost-benefit analysis for each concept, including “constructability,” environmental impacts, equity, funding, maintenance and operations, regional economic impact and seismic resilience and safety.
“After receiving input from Community Task Force members and TAP members in early August, we will finalize the evaluation criteria for the cost-benefit analysis. Meanwhile, we will continue to develop cost estimates for each repair or replace concept and gather the pertinent information needed to evaluate each concept. The cost-benefit analysis will be complete in October and used to inform the city’s decision to repair or replace the bridge,” the SCOT said.