Mayor Greg Nickels has signed off on a b.s. amendment to the state House version of the viaduct replacement bill that would put Seattle businesses on the hook for any cost overruns incurred during construction of the largest deep-bore highway tunnel in the world. Under the amendment, any overruns would be paid for by "property owners in the Seattle area who benefit from replacement of the existing viaduct with the deep bore tunnel." The state has committed $2.4 billion, plus $400 million in tolling revenues, toward the project; as Josh reported this morning, no local government has ever been held responsible for cost overruns on a state-funded project.

Nickels's deputy mayor, Tim Ceis, told the Seattle Times that he was "not going to jeopardize the project over what I see as a fairly petty gesture, a negative gesture, towards the city of Seattle."

Today, mayoral candidate Mike McGinn issued a statement and YouTube video blasting Nickels for "risking the city’s financial health for decades to come.” Although it's unclear what power the mayor of Seattle would have to ignore a legislative decree that Seattle taxpayers pay for overruns, McGinn vowed not to "authorize the use of city tax dollars for the tunnel or associated cost overruns." Nickels has already pledged $900 million in city revenues for the project. The Big Dig in Boston had cost overruns of more than $10 billion; in 2007, 70 percent of Seattle voters rejected replacing the viaduct with a cut and cover tunnel.