Missing from Oahu rail from the start has been an honest broker to independently verify city claims of costs, benefits and options.

Absent this check, city leaders have run a political shell game, getting rail approved by lowballing costs and exaggerating benefits, then arguing it’s too far along to stop when their cooked numbers were exposed.

Now, with rail at least five years behind schedule and $5 billion over budget, the Legislature is our last hope of playing honest broker by demanding real costs and a sound recovery plan before throwing more good money after bad.

Senate Ways and Means Chairwoman Jill Tokuda seemed up to the task last week when Mayor Kirk Caldwell came pleading for another extension of the half-cent rail excise tax — two years after saying the previous five-year extension would be enough.

Tokuda departed from the protocol of letting the mayor testify first, making him sit through testimony from constituents fearful of Oahu’s future swirling down his rail sinkhole.

Then her committee rejected the permanent rail tax extension Caldwell wants, giving him only a return of the state’s 10 percent skim of the tax, worth about $300 million.

She suggested the mayor and City Council might vet rail finances more diligently if they have to pay for it from their own budget and tax resources instead of getting a state bailout.

It brought cries that Tokuda is ducking a solution, but there is no solution with the scant facts before us.

Caldwell won’t say what he thinks the final cost will be to finish rail to Ala Moana Center; few believe the current $10 billion estimate will hold with 21 stations and the trickiest half of the guideway through urban Honolulu still unbuilt.

The city has offered few plans to contain costs and dismisses without honest analysis potential options such as stopping at Aloha Tower or running the last 5 miles at ground level instead of elevated.

A permanent tax extension is essentially a blank check that would let the city continue its slapdash management with no course correction whatsoever.

The city is trying to stampede legislators based on a supposed Federal Transit Administration threat to cut off the $1.5 billion federal share without new local funding by April 30.

But it’s unclear where FTA stands under the Trump administration, and it has so far declined requests to brief the Legislature and public, who must get agency views secondhand through self-interested city officials.

Tokuda is right — how can lawmakers responsibly extend taxes until the city and FTA fill in the gaping blanks, even if it takes until the 2018 Legislature?

It’s not like rail work will stop; the city has money to finish the segment to Middle Street, where it can feed into the bus system.

Reach David Shapiro at volcanicash@gmail.com.