Report: Seattle's Alaskan Way Viaduct safe for drivers

SEATTLE -- An independent report released Monday found that while safety concerns exist, Seattle’s Alaskan Way Viaduct can remain open to drivers.

The aging viaduct suffered damage during the 2001 Nisqually earthquake. More recently, signs of settling and cracking prompted transportation officials to hire the engineering firm CH2M HILL to conduct a review of the structure’s integrity.

“The report’s conclusions support the Washington State Department of Transportation’s decision to keep the viaduct open to traffic,” the Seattle Department of Transportation wrote in a statement. “However, refinement of some of WSDOT’s analysis of certain portions of the structure is recommended, especially because additional settlement is expected from continuing tunnel construction activities.”

Signs of settling and cracking started to surface after 2012, when work began on a deep bore tunnel to replace the two-story viaduct.

The tunnel boring machine, nicknamed Bertha, is in the process of being repaired after suffering serious damage underground. Seattle transportation officials said Monday that before she can start moving again WSDOT must complete additional analysis of the viaduct.

The independent report also suggested that the viaduct continue to be monitored very closely, especially once tunneling resumes.

“Given the current condition of the viaduct structure and the magnitude of the observed settlements, the viaduct should be actively monitored for any additional differential settlement as well as any signs of distress,” the report stated.

Questioned by members of the Seattle City Council on Monday, transportation officials could not say at what point the viaduct would no longer be safe for everyday use.

If the viaduct were to fail before the tunnel is complete, the city could face traffic gridlock. The tunnel is not expected to open to traffic until the end of 2017, which SDOT said is two years longer than previously planned.

Read the entire report here.