The city council is slated to vote on a bill this afternoon that would enact a memorandum of agreement between the city, county, and state, setting up a plan for construction and funding of the massively controversial tunnel option for replacing the Alaskan Way Viaduct. If passed, the ordinance wouldn't commit to anything that hasn't been discussed already, but it would declare the tunnel option to be the city's preferred replacement option.

Seattle's commitment to covering cost overruns isn't explicitly spelled out in the memorandum or the council bill, but both refer to last year's state Legislature bill—which caps state spending at $2.4 billion caps toll revenue at $400 million, and puts the city on the hook to pay for any extra expenses over the budget. But the Legislature's bill is strikingly vague about who would end up picking up this tab. Anything exceeding the $2.8 billion mark "shall be borne by property owners in the Seattle area who benefit from replacement of the existing viaduct with the deep bore tunnel," the state law reads.

There's dispute over whether this provision—making Seattle taxpayers responsible for overruns on a state highway—is enforceable. But if it isn't, why is the city council blessing it?

UPDATE:The council passed the tunnel plan unanimously.