Key state lawmakers say they need more answers on just how much of rail’s giant $1.4 billion contingency pot the city really needs before they’ll consider approving another tax extension to rescue the project.

During a tense hearing earlier this week at the state Capitol, a visibly frustrated Sen. Jill Tokuda questioned why those dollars are even called “contingency,” which is generally understood to refer to a rainy-day fund, when local rail officials say they’ll almost certainly spend that entire amount.

“We’ve been going through this entire process over the last few years thinking contingency is exactly that: contingency. In fact, contingencies are real costs,” Tokuda (D, Kailua- Kaneohe) told Honolulu Mayor Kirk Caldwell on Monday. Caldwell had just lobbied the state Legislature to extend Oahu’s 0.5 percent general excise tax surcharge in perpetuity to cover rail costs, including the mounting budget deficit to build the system.

“Don’t call it a contingency if it’s a real cost. Get real about exactly how much this is going to be,” Tokuda, chairwoman of the Senate’s Ways and Means Committee, told Caldwell as other city and rail leaders looked on.

They’ll now have to hustle to show Tokuda and other lawmakers why they need all of those dollars and, ultimately, secure another tax extension. The city faces an April 30 deadline to provide the Federal Transit Administration with its “recovery plan” detailing how it plans to overcome rail’s financial woes.

Earlier in the hearing, Caldwell told members of the Legislature’s money committees that he still couldn’t say for sure how much it would cost to build the full 20-mile, 21-station system. He further suggested rounding rail’s latest roughly $9.5 billion estimate, which includes financing, up to $10 billion. The project faces a renewed budget deficit of about $3 billion.

Several lawmakers expressed support to once again help by extending the surcharge. The project could lose its $1.55 billion in federal funding, see a severe drop in ridership and put a heavier burden on the city to subsidize if it doesn’t go to Ala Moana Center. However, Tokuda said the city still isn’t providing enough detail or proof that it’s finally gotten a handle on project costs after the Legislature last approved a five-year tax extension just two years ago.

“We need to know how much you actually need,” Tokuda told Caldwell. “You’re asking us (for an) in-perpetuity extension. At this point in time I don’t have a good handle on your numbers. … I have major concerns about this.”

With input from federal officials, the project’s contingency has grown instead of shrunk as more of the rail line gets built. The contingency pot went from nearly $644 million in 2012, representing about 13 percent of the total construction cost, to $1.4 billion today, representing nearly 20 percent.

Meanwhile, the rail system’s federally contracted overseers and the city auditor have previously raised concerns that the Honolulu Authority for Rapid Transportation hasn’t done enough to control costs.

HART Project Director Sam Carnaggio told Tokuda that since spring the agency has been using a new “aggressive” risk management program that works “successfully.” However, it’s been used only on change orders and existing construction — not on any new contracts, Carnaggio said. Tokuda remained skeptical.

Unless HART and the city can better account for why so much contingency is needed, she suggested state lawmakers consider disregarding that $1.4 billion pot altogether. Then, if they provided rail with several hundred million more dollars by eliminating the state’s 10 percent fee on the GET surcharge, it might be enough to complete construction.

That could also give the city a big incentive to rein in costs and avoid using any of the $1.4 billion contingency, she added.

The Legislature will continue to discuss what to do about the tax extension request in the weeks ahead.