As city and state operations grab more new taxes for Honolulu’s rail system, it would be a good time to spell out in a clear, organized fashion who pays for the city’s rail transit system.

It is not just obsessive left-brain thinking to want to see who is paying for the 20-mile system.

There are lingering questions about why the rail system exploded in cost, now pegged at $11.4 billion and once estimated at just $5.2 billion.

Last week the city officially designated a new hotel room tax as the new source of funding for the rail system.

According to a Honolulu Star-Advertiser report, by snagging a portion of a new city-initiated hotel room tax, the rail line will collect a total of $350 million from the tourist tax.

Here is where the questions start. Obviously the big one is what the final cost will be. And in some ways, the question of how we know when we are finished is another unknown.

Honolulu mayors — from Mufi Hannemann, through Kirk Caldwell, Peter Carlisle and now Rick Blangiardi — have all professed a desire to run rail to Ala Moana Center. But now there is talk of stopping early — so when does “pau” mean PAU?

In 2016, Caldwell told the Honolulu Authority for Rapid Transportation board: “Let’s do a good job for the first 15 miles and then we can talk about the rest later.” Later he changed the goal back to Ala Moana. Current Mayor Blangiardi appears to also suffer from some “waveritis,” saying that right now he is confident that the project had enough funding to get to the Civic Center.

“Beyond that is where the problem lies,” he said.

“That’s where the current deficit, I think it was reported at $1.97 billion, lies.”

But both Caldwell and Blangiardi can read a map: Middle Street or downtown, neither is also called Ala Moana Center. So when do we stop?

What HART needs to do is reformulate its questions. Instead of searching for the essentially unknown answer to the question of “How much is rail costing?” just list how much money you have.

That task should keep City Hall and HART busy for some time.

The first question is, how much money do you really have? It is tricky because now that the city passed the hotel room tax, rail has a new source of income, which means the city can borrow against it by selling bonds. But bonds are not free; there is interest attached.

When you go to the bank to get a new mortgage, the bank won’t take guesstimates for how much money you have, how much you earn and what you owe. The bank wants black-and-white answers to those questions. The city needs the same black-and-white thinking with rail.

If HART can just come up with a figure for how much it can spend, then it can start talking rationally about where the rail is going and when.

Richard Borreca writes on politics on Sundays. Reach him at 808onpolitics@gmail.com.