The rush to replace the Tappan Zee Bridge shows few signs of slowing as the New York State Thruway Authority seeks to borrow $500 million to get its photo-ready shovels in the ground early this year.

The bonding plan announced last week follows the selection of a builder in December and the rapid sign-off of that contract by state Comptroller Thomas DiNapoli. Each move lessens the likelihood that Gov. Andrew M. Cuomo's signature project will stall before the heavy lifting begins.

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The short-term borrowing, however, highlights what could be the Achilles' heel of the project -- there's still no funding plan in place to pay for the new span, pegged at $3.1 billion.

The Cuomo administration is waiting on a federal loan from the U.S. Department of Transportation that could cover up to half of the construction costs. If it's authorized, the $500 million would be repaid from the loan.

New York is likely to get the loan, but the "if," "when" and "how much" hover over this project like a dense Hudson River fog.

The state and federal government are clearly working on different timetables -- and that could hurl bridge-rattling gales at the project's strict schedule, which includes an abbreviated four-month dredging season set to begin in August.

Cuomo has said this bridge will get built regardless, though a financial plan, with details on potential toll hikes, appears far off.