SEATTLE - The Alaskan Way Viaduct has sunk more than an inch since crews pumped out groundwater to build a repair pit for the tunnel machine, Bertha.
State officials say the settlement has been even and the viaduct remains safe.
But what if it keeps sinking and becomes damaged to a point it has to close?
"We have a plan that we could deploy," said Richard Sheridan of the Seattle Department of Transportation.
He said city workers are now reviewing an emergency traffic plan from 2005, developed with an earthquake in mind.
Eighty-five thousand vehicles a day drive State Route 99.
The city says it would divert northbound traffic from near Spokane Street to First and Fourth avenues.
Southbound traffic would be detoured to Denny Way and then Second Avenue.
There's less room for vehicles now on Second, because of a new bike lane, but SDOT doesn't see that as a problem.
"If you're someone who can take advantage of biking rather than driving, that's something we would recommend if the viaduct were not available for use," Sheridan said.
The city says it might take away street parking to ease congestion.
Police officers would direct traffic, signals would be re-timed and permits to close streets for new building projects could be revoked.
None of the measures could replace the capacity of the viaduct, which means traffic could be gridlocked.