The number at the core of Honolulu’s undertaking to build a fixed-rail system — $5.17 billion — is frightening, all by itself. So it certainly wasn’t surprising that Honolulu officials and taxpayers blanched at the news about the financial worries of the companies behind the design and construction of the project. Any other reaction would have been irrational.

Honolulu Authority for Rapid Transportation, the entity that is overseeing the project, paused last month before finally signing a $1.4 billion contract with Ansaldo Honolulu JV, the joint venture that now is in line to design, build and operate the train system. It did so with added prodding from the Honolulu City Council. The reason: reports of major financial losses by its parent company, Finmeccanica SpA.

It’s not Finmeccanica on the signatory line, but the concerns centered on prospects that Finmeccanica might sell AnsaldoBreda, a minority partner in the joint venture but the entity that would build the rail cars. Compounding that was the lingering nervousness over a rough patch in AnsaldoBreda’s earlier deal for rail cars in Los Angeles.

All of this is nail-biting material, but HART officials make a persuasive case that the risk is acceptable, pointing to multiple protections for the interests of the city’s taxpayers.

Members of the authority met last week with the Star-Advertiser editorial board and outlined key points:

» In order to back out of the contract at this point, the city would have to demonstrate that there had been a material change in the financial capacity of the joint venture. There was nothing to back such a finding.

» The majority partner in the venture — the subsidiary AnsaldoSTS, with an 80 percent share — would be bound to find another supplier for the rail cars, should AnsaldoBreda be unable to fulfill its part.

» The project is fully bonded to cover any losses that would result.

» Finmeccanica has committed in writing to ensure compliance of contractual obligations, "regardless of any change in ownership or financial capacity of the partners of the joint venture, Ansal-doBreda and AnsaldoSTS."

» A generous contingency fund of $860 million is required by federal authorities and provides further security against cost overruns.

There are many more stress points, of course. First and foremost, there is the lawsuit filed in U.S. District Court by plaintiffs, including former Gov. Ben Cayetano, who argue that the city bypassed exploring alternatives before deciding on a steel-on-steel system.

HART officials rightly fear delays could endanger the city’s place in line for the hoped-for $1.55 billion in federal funds and cost millions if contracts then would have to be unwound.

Still, the city makes a strong argument that alternative technologies were adequately explored in the years of planning preceding the final commitment to steel-on-steel. And plaintiffs face an uphill battle in proving capriciousness on the city’s part, given that the entire process was vetted by the Federal Transit Adminis-tration and congressional overseers, too.

Further, the financial plan submitted by the city before it can enter into the final design phase appears to be sound. It’s a good sign to see that the local funding mechanism, the general excise tax surcharge, is projected to pay off the capital debt before it sunsets in 2023, which will make the operational and maintenance costs more sustainable over the long term.

The more persistent concern that taxpayers should have, looking ahead, is that the highest level of care and transparency is applied at every stage of review. As HART examines various ways of curbing costs through the design and construction phases, the public should be informed about the potential costs and benefits.

This is undeniably a nerve-wracking time for Honolulu and its transit planners, but it appears that enough safeguards are in place to get Honolulu to the finish line: having a more reliable and robust transportation system.

That will be worth enduring a ride that’s been pretty bumpy to this point.