Seattle scales back earthquake work on city bridges as costs soar

After promising Seattle voters that the city would reinforce 16 bridges to better withstand earthquakes, the Seattle Department of Transportation now says that work would cost hundreds of millions of dollars more than once expected.

Instead of 16 bridges, the city plans to complete seismic retrofits on 11, leaving notable and costly locations like the Ballard and Fremont bridges off the list.

Costs for some bridges increased by several million dollars, like a span along 15th Avenue in Ballard now set to cost about $5 million instead of $1 million. Other estimates rose by far more: Improvements to a First Avenue South bridge over a rail yard went from an expected $4 million to $254 million. That cost for a single bridge is more than triple the amount SDOT had planned to spend for retrofitting all 16 bridges. 

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All told, the estimate for retrofitting the 16 bridges soared from $67 million to $731 million.

City transportation officials say deeper study of the bridges revealed expensive work related to the foundations that run underground and are surrounded by soil that can be at risk of liquefying during an earthquake.

With the specter of the Big One, local and state governments have been under pressure for years to do more to prepare. In Seattle, the cuts to seismic work are the latest trouble for the Move Seattle levy, a $930 million property tax package voters approved in 2015. City officials scaled back planned work under the levy after acknowledging costs were rising and City Hall had promised more projects than it could finish.

The city’s bridges have come into new spotlight this year, as the city shut down the West Seattle Bridge due to cracking and SDOT told city auditors the department should be spending at least five times as much as it currently spends on bridge maintenance. Earthquake improvements, though, received less outside attention and weren’t considered in the audit report.

Even as the city scaled back the Move Seattle levy in 2018, SDOT said it could continue to deliver on seismic retrofits for the 16 bridges promised to voters. 

The seismic work was “on track,” the department wrote in April 2018. This year, SDOT leaders revealed to a citizen oversight committee that was no longer the case. 

After city staff and outside consultants assessed each of the bridges and what retrofits were needed, costs on all but two of the 16 bridges rose.

“We had to start with some base assumptions,” said Lorelei Williams, SDOT’s deputy director of capital project delivery. “The ultimate design is just much more involved than we had anticipated.” 

The city’s spending plan in 2015 assumed levy money for seismic work would be paired with $37 million in federal grants and other outside money. The city has received far less in grant money — $3 million so far — though an SDOT spokesperson said the lack of grant funding has “not negatively affected this program.”

In Pioneer Square, about 27,000 drivers a day travel on an elevated span of Fourth Avenue South passing by Union Station. Seismic work SDOT initially said would cost about $9 million is now expected to cost $109 million.

Farther south, another Fourth Avenue South bridge crosses the Argo rail yard between Sodo and Georgetown. There, the estimated cost for retrofits rose from about $4 million to about $249 million. The city closed a northbound lane on the bridge in 2017 because of deterioration caused by heavier loads and aging of the bridge, according to SDOT.

Seismic retrofits for another bridge over the same rail yard, on First Avenue South, would also cost about $254 million, compared to an initial $4 million estimate. The bridges over the rail yard, built in the 1930s, each carry 17,000 to 22,000 vehicles per day, according to federal data. 

In Fremont and Ballard, costs for the 103-year-old bridges over the ship canal rose from about $7 million each to $29 million and $32 million, respectively. The Ballard Bridge carries about 54,000 vehicles a day and the Fremont Bridge carries 28,000.

As SDOT and its consultants began to study the bridges and run them through earthquake simulations, they found needed work not just on aboveground structures, but in foundations that run below the ground or underwater, said SDOT roadway structures Director Matt Donahue. 

In some cases, those foundations are surrounded by soil that can liquefy during an earthquake, creating the need for various work to strengthen that soil, as was done near the downtown seawall, where crews injected grout into the soil. 

“It’s very difficult for complex bridges to really know what the as-built analysis is going to reveal until you do it,” Donahue said.

Certain areas of Seattle are at a well-documented risk of liquefaction. A map released by the city the same year the levy went before voters shows swaths of industrial land in the city are at risk of liquefaction, including the areas where the Fourth Avenue bridge and the bridges over Argo rail yard are located.  

For some of the bridges SDOT planned to retrofit, “those soils were a lot more susceptible to seismic forces than was previously thought,” Donahue said.

Work on underground bridge foundations is a common cost driver, said University of Washington civil engineering professor Marc Eberhard. When costs for seismic retrofits rise high enough, governments may consider wholesale replacement of the bridges instead.

“If you start trying to fix the foundations, your prices go up exponentially,” said Eberhard, who has advised governments on seismic safety but is not currently under contract with the city. 

Locations near water or rail yards can drive costs because equipment needs to be arranged under water or in a way that allows railroads to continue operating.

To retrofit bridges for earthquake conditions, crews can use carbon fiber wrap to strengthen parts of the bridge, similar to some of the work being done on the West Seattle Bridge. They can also use restraints to essentially tie the upper part of a bridge to its foundation, preventing the two parts of the structure from sliding in different directions during an earthquake and splitting apart. 

Most of the bridges SDOT has studied need a combination of these methods, Donahue said, and some need soil work.

Now, SDOT plans to remove the most expensive bridges from its immediate plans and move ahead with others, like the Admiral Way bridge in West Seattle, 15th Avenue over Leary Way in Ballard and several pedestrian bridges. Work is already done on the Cowen Park Bridge in Ravenna and underway on the West Howe Street Bridge in Magnolia.

Levy opponent Eugene Wasserman said the cutbacks reflect neglect of the city’s oldest bridges.

“The levy money should be used for the most potentially devastating things and that is the Ballard Bridge going down,” said Wasserman, president of the North Seattle Industrial Association, made of industrial and maritime businesses along the ship canal. The city has studied replacing the Ballard Bridge, but has not funded a new structure.

Williams said SDOT is drafting a plan for needed work on all of its bridges and other structures, which will include the earthquake work dropped from the levy. That plan is due in 2023.