New York State Comptroller Thomas DiNapoli on Thursday approved the Thruway Authority's first steps to financing work on the new Tappan Zee Bridge.

Even as he approved the January sale of $500 million in bonds issued by the Thruway Authority, DiNapoli reiterated unanswered questions about how the state would the cover all the costs related to the $3.9 billion span.

DiNapoli's move green-lights the consortium building the new bridge, Tappan Zee Constructors, to receive a payment of $125 million, wrote First Deputy Comptroller Pete Grannis in a letter to Thruway Authority Executive Director Thomas Madison.

That funding covers the builder's cost of setting up staging areas in South Nyack and Tarrytown in March, the first step for the five-year megaproject, said Thruway Authority spokesman Dan Weiller.

"We appreciate the approval of this bond issuance," Weiller said in a statement.

Grannis noted that the Thruway Authority also has the option to float an additional $200 million in bonds if it needs more cash for the bridge. The deputy comptroller also cautioned that the Thruway Authority has yet to secure a low-interest loan from the federal Department of Transportation that could fund as much as 49 percent of the new Tappan Zee's total price tag.

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The state has requested the loan from the federal government, which is expected to grant at least a portion of the requested amount. But, as Grannis wrote, "there continues to be uncertainty surrounding the final outcome and timing of this decision."

Grannis also said the Thruway Authority needs to set tolls for the new bridge, which would be used to repay its bonds and the federal loan, but the Authority and Gov. Andrew M. Cuomo have yet to say how much commuters will dole out to cross the Hudson River on the span.

Last summer, Cuomo officials said tolls on the new Tappan Zee would need to increase from $5 to $14 by 2017 to cover debt service on the bridge. The announcement sparked outrage from commuters.

The governor responded by saying $14 was too high and that he would appoint a panel to study prospective tolls. Since then, state officials have been mum on the topic.

"Transparency demands that the Authority make public a full financing plan, including the expected level of tolls, as soon as possible," wrote Grannis.

At a public meeting on Monday in Tarrytown with Tappan Zee Constructors, Madison said toll rates would depend on the size of the federal loan. State and federal officials are in regular contact about the loan application, he noted.

"The Thruway Authority has been committed to complete transparency and openness...," Grannis said, "and we will continue to hold this project to that high standard."