Mayor Kirk Caldwell and City Council Chairman Ron Menor think Oahu taxpayers are so rich we can pay not only for a $10 billion rail system that’s $5 billion over budget and climbing, but also for road projects on the neighbor islands.

The two offered leery lawmakers a ludicrous bribe if they bail out the city from its rail deficit by extending the Oahu’s half-percent rail excise tax surcharge.

They invited the state to increase its controversial 10 percent skim of the tax to 20 percent or 25 percent, which could boost the state’s annual rake from nearly $25 million to more than $60 million.

Most preposterously, Caldwell suggested these funds raised solely from Oahu taxpayers be used for projects such as a highway widening on the Big Island and a bypass road on Kauai.

Adding a 25 percent political premium to a grossly expensive project that’s already wildly over budget would move Oahu rail past train-wreck status to bats-in-the-belfry crazy.

The scheme comes the same week a University of Hawaii study called the state’s skim exorbitant and said it should be cut to 1 percent or less.

Caldwell has been mired in rail’s dysfunction since 2008, when he was former Mayor Mufi Hannemann’s self-described “primary point person” on the project.

He’s lost any conscience about the burden he’ll put on his constituents to avoid needed cost-cutting adjustments as he and his cohorts continue to bungle rail.

It’s easy to give away taxpayers’ money when you’ve got it made with a $165,000 mayoral salary and a $200,000-to-$300,000 side job at the bank.

But the excise tax he’s so eager to spread around must also be paid by a homeless mother buying milk for her kids or a hardworking laborer who will never be able to afford one of the luxury condos along the rail route.

Caldwell himself complained in 2011 that the state’s skim, intended only to cover the cost of collecting the rail tax for the city, yielded enough to pay for the entire operation of the state tax department.

Gov. David Ige says he’s depending on the state’s rail-tax share to cover an $80 million upgrade to the tax department’s computer system.

Why should Oahu taxpayers alone bear the cost of the tax department or a computer system that serves the whole state?

Charging one county’s residents a higher tax to fund projects in other counties is unprecedented and possibly unconstitutional.

If rail-tax revenues are to be spent statewide, the tax should be levied statewide. (Hear neighbor islanders scream about having to help pay for Oahu rail.)

Let’s hope Oahu legislators, a sizable majority, have more scruples than our mayor and Council in protecting their constituents and will scuttle this shabby ploy.

Reach David Shapiro at volcanicash@gmail.com.