West Seattle Bridge repairs may or may not work. The Port of Seattle, city of Seattle and Sound Transit need to plan for a replacement.

Gothenburg, Sweden, is the largest port in Scandinavia. Last week, the city opened its second immersed tube tunnel, the Marieholm Tunnel. Gothenburg’s first immersed tube tunnel, the Tingstad Tunnel, was built in 1968. Together these tunnels can carry a total of 180,000 vehicles a day with little impact on the river and its riverbanks.

The Marieholm Tunnel is six lanes, crosses a 1,000-foot wide river and cost 170 million euros ($225 million). A Duwamish Tunnel would be six lanes, with a 500-foot wide river crossing and cost $2 billion, according to the Seattle Department of Transportation’s wildly inflated estimate. Sweden is not a low-wage country, and Swedish engineers and contractors are not that much better. Assuming SDOT’s bridge replacement estimate of $564 million is more accurate, and based on the Marieholm Tunnel’s cost of $225 million, a tunnel under the Duwamish could be built for less than a replacement bridge. A tunnel can also accommodate light rail better than a bridge, and be many times more earthquake-resistant.

Bob Ortblad, MSCE, MBA, Seattle