The MTA's police chief is stepping down on January 5.
Owen Monaghan will retire after leading the agency's police department since 2017.
He served 34 years with the NYPD before that.
Word of his retirement comes a week after the MTA board voted to hire 500 additional police officers to patrol the subways and buses.
Critics say the new officers are not needed because subway crime actually is down. The MTA counters that fare evasion and assaults on transit workers are up.
The MTA police chief of operations, Joseph McGrann, will take over Monaghan's role on an interim basis.
A nationwide search for a full-time replacement will ensue.