To borrow the old transportation metaphor: The rail project is at a crossroads, given the news over the weekend of some truly stunning cost estimates for the completed project.

The $6.9 billion figure arrived at by the Honolulu Authority for Rapid Transportation was startling enough. But, as Honolulu Star-Advertiser writer Marcel Honore reported Sunday, federal officials overseeing construction of the 20-mile system estimate an even more harrowing bottom line: $8.1 billion.

As HART and city administration officials are already suggesting, the sticker shock absolutely underscores the need to take stock and consider all the options that could contain costs. The public has been promised a chance to weigh in, which is essential.

But above all, while officials move quickly to examine the issues as they should, taxpayers need straight talk about the real costs that are likely for each alternative. And, they need to be clear-eyed enough to see that costs come with each change, and consider that many of the options could lead down a rabbit hole of additional delays and overruns.

Colleen Hanabusa, the former congresswoman who now chairs the HART board, agency Executive Director Dan Grabauskas, city Transportation Services Director Mike Formby and others got the bad news in meetings with federal authorities last week.

Contrary to local officials’ previous expectations, now the feds seem more open to major cost-cutting avenues. Among the ideas being floated is a reduction in the number of rail cars and, given that some cities have seen ridership soften a bit, that’s worth a look.

So is the notion of reducing the number of stations among the 12 that remain to be contracted out. Down sides — such as the loss of convenience when stops are spaced out, and the loss of redevelopment opportunities to add to Honolulu’s affordable rental stock — must be factored in, too.

None of this negates the need to clamp down on constantly rising expenditures, through oversight of the existing contracts. Grabauskas has cited Oahu’s superheated construction market as the cause, draining the the available workforce and driving up bid prices.

But HART has never demonstrated it’s had sufficient cost controls; more hard-nosed oversight over the contractors and subcontractors is necessary. Taxpayers now have little confidence that Honolulu is getting its money’s worth.

The recent increases have been due to unanticipated additional costs in the development of the alignment’s second half, heading into town. That bill will become plain when the contract for these stations is awarded, or at least publicized, in the next few months.

Among the chief worries is that building the guideway with sufficient safety clearance of the high-power utility lines will be much more expensive than anticipated.

Of course, these costs were knowable in advance. HART and the power utility, Hawaiian Electric Co., should have communicated with the public, and each other, much sooner. Now both parties must work cooperatively to arrive at a compromise that does not add undue burdens to the taxpayer who is ultimately paying these bills.

Hanabusa said she doesn’t believe state lawmakers will agree to a further extension of the general excise tax surcharge funding the project. Regardless, more funds will surely be needed.

Seeking a further extension must be among the options on the table, as well as the return of the 10 percent of the transit tax the state skims off each year. Lawmakers can’t justify continuing to keep the skim, plain and simple.

The HART board will be under considerable pressure to yield to proposals that the rail project simply be ended at Middle Street, compelling commuters to transfer to buses at that point. And Formby has floated the idea of continuing the line from that point with an at-grade light rail section into town.

The light rail conversion deserves a look — but when all the costs for studies, expanded route disruptions and business impacts are examined, that could be a fool’s bargain.

And simply ending it at Middle Street is a nonstarter. The result would be a rail system that solves precious few traffic problems. The object of the project was to make an onerous commute more convenient and comfortable, not a two-stage ordeal, dropping people off far from their desired destination. Who would be lured out of their cars for that?

Rather than pulling the circuit-breaker on the project, HART and all elected officials should do their collective job: Manage those costs and that disruption. Consider the alternatives, but only those that can deliver a transit system that serves Oahu’s needs.