Local rail leaders have raised their estimate yet again for how much it will cost to complete the cash-strapped 20-mile transit project, now putting the price tag at more than $8.6 billion.

They’ve also added another year of delay to rail’s schedule, mostly thanks to the ongoing dilemma about how to fund the elevated project’s final leg into town. Rail leaders now estimate that train cars will start running across the full line from East Kapolei to Ala Moana Center starting in December 2025.

Originally, under the city’s deal with federal transit officials, the rail was supposed to cost $5.26 billion. The full line was to start running in January 2020.

The latest price tag is $700 million more than the figure the Honolulu Authority for Rapid Transportation issued nearly four months ago, in early June, when it estimated the transit line and its 21 stations would cost $7.9 billion.

The updated figure includes hundreds of millions of dollars more set aside for contingency and to eventually build rail’s final 4 miles or so into Honolulu’s urban core, HART board Chairwoman Colleen Hanabusa said after the group’s meeting Thursday.

It also includes some $200 million to deal with utility clearance issues on the west side; the amount would be sufficient to put the utilities there underground if necessary, rail officials said.

“It is an estimate. We’ve asked staff to be as accurate as they can on this,” Hana­busa said, adding that the figures could change even more than they already have in the past two years.

Hanabusa, who’s now running for her former congressional seat, plans to leave the HART board before the Nov. 8 general election. However, the rail leaders who replace her and the rail agency’s acting executive director, Mike Formby, will have to strike a delicate balance, she acknowledged.

Those leaders will have to manage the public’s expectations with the project’s seemingly ever-shifting price tag — but they’ll also have to present solid budget numbers to state lawmakers if they’re to secure more general excise tax dollars to finish the full project.

“Going back to the Legislature, you don’t want to make the same mistake you did last time (during the 2015 legislative session) where you say a billion and a half (dollars) will cover us,” HART spokesman Bill Brennan said. The worst thing to do is to underestimate the amount that’s needed, he added.

HART officials this summer had put the cost of rail at about $8.3 billion, which they said included some $300 million in financing costs. However, Hanabusa said Thursday that the $7.9 billion was the correct figure, and the one the public should use to compare “apples-to-apples” to HART’s new $8.6 billion estimate.

Around the same time, rail’s Federal Transit Administration partners estimated it could cost as much as $8.1 billion. In addition, rail’s federal partners released an “upper-bound” figure of $10.79 billion, although they’ve stressed that’s part of a statistical analysis.

“They’ve asked us not to quote them any more on that number,” HART Project Manager Sam Carnaggio told the board Thursday.

The true cost to build a rail transit system across Oahu’s southern shore has dogged transit officials for years.

Board members fretted over yet another potential price-tag matter at Thursday’s meeting: defective materials on rail’s first 11 or so miles to Aloha Stadium. Construction firm Kiewit Infrastructure West is building that portion of the project.

Cracks are forming in “shims,” the plastic padding used to give the tracks a level surface, and strands in three of the tendons that help keep the guideway structure in place have snapped apart, according to reports issued by HART and the rail project’s federal oversight agency.

At Thursday’s meeting, HART officials said water draining out of the rail guideway’s concrete spans apparently seeped into some of the anchors that lock the steel tendons to the structure, causing them to corrode. So far, workers have reportedly found three tendons with metal strands that snapped apart.

Investigators also reportedly found that grouting meant to seal and protect the tendon inside ducts is defective. They subsequently used a hammer to inspect the grouting across the full guideway, and individually tested 57 of 1,586 tendons, according to HART officials.

One dozen defective tendons have been replaced, including the three with snapped strands, officials said.

Hanabusa and Taka Kimura, HART fixed facilities design manager, both said they have “serious questions” about whether Kiewit has sufficiently tested tendons to make sure they didn’t miss any more damage along the first 11 miles.

“We need to be able to assure the public that (Kiewit officials) have done everything they can,” Hanabusa said Thursday.

Six tendons stretch through each concrete span of guideway, providing tension to hold it together, according to a HART presentation. If one tendon breaks, testing has shown it would cause stress and cracking but not “catastrophic failure,” Kimura said.

Nonetheless, officials want to be sure the issue is resolved before trains start running across the guideway.

“There’s a concern. You have to come up with something else — and now,” Hanabusa said. “Can you imagine if we have to replace a tendon when the train is running? The whole system’s going to have to stop.”

Detailed rail cost estimate as of Sept. 29, 2016