A New York City Transit employee was killed overnight by a southbound D train while her crew was preparing scheduled track work on a Bronx subway line, the MTA said Friday.

Moet McCullum, a 38-year-old mother of two, was preparing to set up flags on the tracks between the 167th St. and 161st. St. along the D line in Highbridge when she was hit by an oncoming train shortly after 11:30 p.m. Thursday, multiple transit sources told the Daily News.

McCullum was in the process of setting up the flagging lights that warn oncoming trains to the presence of a work crew. The operator of the D train reported not seeing any such flags before striking McCullum, according to sources.

The track worker was taken to Lincoln Hospital, where she died.

McCullum, who also worked as a conductor for NYC Transit, had been on the job for less than a year, according to payroll records and transit sources.

“This is a difficult day,” NYC Transit President Demetrius Crichlow said in a statement. “Last night, we tragically lost a member of our MTA family.”

“I was at the hospital last night, and this morning I was at the scene, and I met with her family,” Crichlow said. “I have also spoken with [MTA] Chair [Janno] Lieber and TWU Local 100 President John Chiarello — all of us are heartbroken. I ask that we all keep Ms. McCullum and her family in our thoughts and prayers.”

Crichlow said the incident is under investigation. In a social media post Friday morning, the National Transportation Safety Board said it was sending a team to New York to investigate McCullum’s death.

“Flagging” — the act of warning oncoming trains that there are track workers up ahead — is regarded as among the more dangerous tasks in subway track work.

NYC Transit worker Hilarion Joseph was also in his first year on the job when he was struck by a D train and killed while flagging for a track-cleaning crew in November 2023.

Another flagger, not publicly identified, suffered severe head trauma in 2024 after he was hit by an out-of-service F train in Brooklyn.

Both incidents were cited in a scathing Federal Transit Administration assessment in 2024, which demanded the MTA improve its safety procedures and the state’s Public Transportation Safety Board to step up its oversight of New York City Transit.

The MTA appealed that report, saying its findings mischaracterized the agency’s safety record.