Another Oahu rail official has left the project.

Diane Arakaki resigned and departed as the Honolulu Authority for Rapid Transportation’s chief financial officer on Dec. 15, according to the rail agency’s latest monthly status report. Arakaki was HART’s CFO for more than four years.

Attempts to reach Arakaki for comment Thursday were unsuccessful, and a HART spokesmen said he didn’t have a reason for her departure.

She’s the latest of more than a dozen prominent personnel to leave HART in the past two years — a trend that has raised concerns among the agency’s board, Honolulu’s mayor, and, most recently, outside officials conducting a peer review for rail’s federal partners.

Last week, a team with the American Public Transportation Association visited HART’s Honolulu offices and rail construction sites to review how well the project is being managed. Their report is due out in mid-February, but among their preliminary findings the team cited a “loss of institutional knowledge due to staff turnover,” said Krishniah Murthy, HART’s interim executive director, who started work Dec. 5.

Honolulu Mayor Kirk Caldwell testified before the HART board last month that he had asked his staff to compile a list of those who recently left the agency and the salaries they earned.

“Many of them that left were some of the most highly compensated people in the city,” Caldwell told the board at its Dec. 15 meeting. “It begs the question: Are they leaving because of pay, or are they leaving because of management?”

With rail costs and schedule delays increasing, “it’s probably not the best place to work,” Caldwell added. “We want to keep those folks” and make HART a better working environment.

HART leaders, including board Vice Chairman Terrence Lee, have also expressed concern over the agency’s “revolving door.”

HART has offered the CFO position to someone who has accepted but hasn’t yet signed an employment agreement, agency spokesman Bill Brennan said. That person, Arakaki’s replacement, is tentatively scheduled to start in February, he added.

Additionally, HART’s former deputy director of planning, Jon Nouchi, left the agency the day after Arakaki, Brennan said. Nouchi’s LinkedIn social media profile lists him as joining HART in May 2014. He’s now deputy director for the city’s Department of Transportation Services.

HART is proceeding with its search for a permanent CEO to take over in about a year, board member Colbert Matsumoto said.