The largest crack on the Alaskan Way Viaduct grew by 3 millimeters in the past six months, and the state is deciding whether the roadway...

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The largest crack on the Alaskan Way Viaduct grew by 3 millimeters in the past six months, and the state is deciding whether the roadway needs to be repaired.

State officials say there is no safety problem on the bridge because of the growing crack, which has expanded from 4 to 7 millimeters.

Yesterday’s announcement about the crack followed a weekend inspection of the bridge. But engineers found no new settling of the support piers had occurred on the viaduct, which was built in 1953. Increased settling could have meant costly repairs, such as bracing and strengthening the footings of the viaduct and perhaps keeping heavy trucks off the road.

The state conducts full inspections of the viaduct every six months. It has been watching a section near Columbia Street and Yesler Way, which has settled about 4 ¼ inches. Last year the state determined that if that section should settle a total of 6 inches, repair would be needed.

“There’s no settlement and no emergency,” said Linda Mullen, spokeswoman for the Washington State Department of Transportation. “The crack is growing, but there’s no negative impact to the rest of the viaduct.”

She said the crack was found in an area near Colman Dock and was in an area the state has been monitoring since the 2001 Nisqually earthquake damaged the viaduct. The state has 30 instruments on the structure to monitor cracks.

The crack is on a joint on the southbound lanes.

“This is just more evidence that the viaduct is continuing to age,” said Harvey Coffman, state bridge-preservation engineer. “This crack does not pose a safety threat, but we will continue to keep an eye on it and decide what repair, if any, is needed.”

The state wants to replace the viaduct, which carries 110,000 cars each day, and money from a new gas tax approved by the Legislature would provide $2 billion, enough to replace the viaduct with an above-ground structure.

But Initiative 912 on the November ballot would overturn the tax, leaving viaduct replacement uncertain.

Susan Gilmore: 206-464-2054 or sgilmore@seattletimes.com