The Alaska Way Viaduct has sunk almost half-inch in a spot where the world’s largest tunneling machine has been chewing a highway tunnel (that is, when the darn thing is working) under downtown Seattle.

Predictably, the state Transportation Department tells us not to worry – that the sinking by four-tenths of an inch is within safety limits and was expected during construction. So, presumably, it’s fine to drive on and shouldn’t collapse anytime soon – or at least until the next earthquake.

Seattle City Councilman Mike O’Brien tells Seattle Weekly, “This thing is a dangerous piece of infrastructure. We may have to shutdown the Viaduct, and that will be a very difficult political decision.”

Adds O’Brien, “I am concerned. We have a structure that we know has been compromised, so the question is, ‘How safe is it?’ We know at some point it’s going to become unsafe…I mean, they’re going to be digging a 120-foot tunnel down to fix [Bertha’s 5-story tall cutterhead]. It’s going to be unsafe.”

Todd Trepanier, WSDOT’s Viaduct replacement project manager, poohed-poohed any such concerns. “This was settlement that was anticipated and known it would happen because of the tunneling activities,” he told the media in a conference call today. “And Seattle Tunnel Partners, as part of the contract, designed for that and strengthened the viaduct to be able to deal with those settlements,” Todd Trepanier, WSDOT’s Viaduct replacement project manager, told the media during a conference call on Tuesday.

He added that the viaduct has been settling for years in varying amounts along the entire stretch of the elevated roadway. It remains vulnerable to earthquakes, and WSDOT has an emergency closure procedure in place in case of a catastrophic event. Short of that, though, there’s nothing to indicate the viaduct faces any undue threats from Bertha, Trepanier said.