The agency overseeing Honolulu’s rail project has agreed to help out the state by replacing outdated traffic signals along the future transit system’s western half, as construction proceeds there.

Under the deal, which members of the Honolulu Authority for Rapid Transportation board approved Thursday, the state Department of Transportation will reimburse HART with federal dollars for the upgrades at some 23 intersections, officials say. The board agreed to a provisional sum of just over $16 million.

HART had already agreed to replace the older poles that come into direct contact with rail there, but the new deal will have the agency’s contractors replace more such traffic fixtures along the project’s first 10-mile stretch.

It’s not clear how many will be replaced there; a HART spokesman was unable to provide those details Thursday.

Nonetheless, the coordination, the agency says, would spare the public that commutes along Farrington and Kamehameha highways in West and Central Oahu from having to endure another round of construction there to replace those decades-old traffic signals with newer, larger ones that can withstand heavier wind and meet new state code.

“We’re trying to work together to minimize the impacts to the public but not adding costs to the project,” HART Executive Director Dan Grabauskas said last month, when the board first discussed the move.

However, Kiewit Infrastructure West, which is building the first 10 miles of elevated guideway, disagrees on the cost of that replacement work — and HART staff has said they could be back before the board to approve a larger reimbursement cost.

Kiewit has estimated the work will cost some $23.9 million, according to Kainani Kraut, HART’s West area contract manager. “There’s a big delta there,” HART board member Terrence Lee said Thursday of the nearly $8 million difference in estimates. HART officials said that much of Kiewit’s bigger estimate is based on “overhead.”

In an email Thursday, Kiewit deferred to HART all questions on the cost to replace the traffic signals.

“Once we receive the change order, we will work with HART to determine the exact impacts to the construction schedule for this additional scope of work,” Kiewit spokeswoman Alyssa Tenorio said in the email.

At their February meeting, board members considered the deal but opted to delay approving it largely out of concerns that the necessary reimbursement agreement with DOT hadn’t been finalized yet. That agreement has since been completed, according to HART spokesman Bill Brennan.