The earthquake-damaged Alaskan Way Viaduct should be torn down and replaced rather than quake-proofed, a team of independent engineers hired by the state has recommended.
In a report to be released today by the Alaska Way Viaduct Structural Sufficiency Team, the engineers said they studied repairing, retrofitting or replacing the viaduct, which was damaged in the Feb. 28 Nisqually Earthquake.
"As a result of our review, the committee recommends the (state Department of Transportation) proceed to replace the viaduct," the six engineers said in a two-page summary report.
"Even though a comprehensive seismic retrofit might achieve a level of safety comparable to a new structure, the eventual deterioration of the current structure due to aging would exact a greater sum of financial resources for maintenance and be less reliable than a new structure built to current seismic design standards."
The engineers found a one-in-20 chance of an earthquake that would cause the viaduct to fail.
"That risk is greater than acceptable - we have to act now," Transportation Department spokeswoman Linda Mullen said.
Replacing the 2.2-mile elevated roadway on the downtown Seattle waterfront would likely cost hundreds of millions of dollars and create a huge traffic mess.
The engineers said replacement should begin immediately and estimated it would take 10 years, the same amount of time required to retrofit the viaduct.
The inspection team was hired by the Transportation Department last month to review viaduct repairs under way and determine whether the structure could be retrofitted to withstand another quake.
But Mullen maintained that even retrofitting must remain an option and said the report would figure heavily in any decisions the state made about the viaduct.
The roadway needs to go to the head of the list in transportation priorities, said Aubrey Davis, a member of the state Transportation Commission.
"We can't wait," Davis said. "If replacement is the only option we have, we have to start right away. We can't wait until it falls down."
But finding the money for a new viaduct wouldn't be easy.
"That's a big chunk of money," said state Rep. Ruth Fisher, D-Tacoma, chairwoman of the House Transportation Committee. "... Wow, things are getting expensive. It's just one more thing to put on our list of things to do - and pay for."
The 48-year-old viaduct sustained major damage in the earthquake. Several cracked columns have caused intermittent closures and weight restrictions, and prompted the state to set aside $5 million to study what should be done about the structure.
That study, set to begin in the fall, will include an environmental review of four options: retrofitting the viaduct, building a new viaduct, replacing the structure with a tunnel or simply tearing it down.
"The reality is, it probably should have been replaced earlier," said Jerry Weigel, a bridge and structures engineer with the Transportation Department. "This is a complex, huge problem."
The viaduct, which carries 100,000 cars a day, one-third of the city's north-south traffic, has been reduced to two lanes in each direction and is closed to northbound trucks and buses.
Initially, Transportation Department engineers believed the viaduct had escaped the earthquake relatively unscathed, but cracks were later discovered in a number of the support piers near the south end of the bridge, leading to emergency closures.
A 1996 study by engineers at the University of Washington found that the viaduct was built on soil that could liquefy in an earthquake. Engineers also found problems in the way the columns were connected to the foundation.
The UW study concluded that retrofitting would cost $340 million, tearing it down about $120 million and replacing it $530 million.
But those numbers are misleading, said Weigel, because they are five years old and do not take into account a new viaduct with increased capacity.
The viaduct cost $8 million to build. It opened in 1953.
The structural-sufficiency team was headed by David Goodyear of Olympia, senior vice president of TY Lin, a San Francisco engineering firm.
The team's recommendation will go to the Transportation Commission. The engineers were asked to look only at the viaduct's seismic safety and structural design, not at planning or capacity issues, nor at what a replacement roadway might look like.
Susan Gilmore can be reached at 206-464-2054 or firstname.lastname@example.org.