Working for the MTA is the fast track to a six-figure salary.

One in four Metropolitan Transportation Authority employees made $100,000 or more in 2014, according to payroll data released by the Empire Center Thursday.

The 21,352 employees raking in the big bucks last year more than doubled the six-figure earners in 2013 — which, at the time, was about one in seven, the data said.

The massive jump includes $431 million in retroactive pay handed out after union contracts were settled, the Empire Center said.

The agency paid out $849 million in overtime last year and $4.7 billion in base salaries to its 76,445 employees. Top earners were a mix of agency heads, supervisors and foremen, the data shows.

The MTA’s single highest paid employee was now-retired Metro-North president Howard Permut at $452,584. Second-highest was MTA chairman and CEO Thomas Prendergast, earning $346,707.

Metro-North Railroad Track Supervisor Robert M. O’Connell was the biggest overtime-earner, raking in $184,634 in OT on top of his $77,478 base salary. Sixty-five other MTA employees earned more than $100,000 in overtime.

The average MTA employee’s salary was almost $81,000 in 2014, up from $73,355 a year earlier.

The MTA Police Department was the most lucrative branch with average pay, including OT, of $135,598. Long Island Rail Road was second, with average pay of $106,000.

“When the MTA settled several outstanding labor contracts last year, tens of thousands of employees who had gone years without a raise received one-time-only payments for retroactive wage increases,” said MTA spokesman Adam Lisberg.

“Thousands of employees reached the Empire Center’s $100,000 threshhold only because they were finally paid for work they had done years earlier, and the Empire Center’s flawed analysis needs to reflect that.”