Overtime costs soared at the Metropolitan Transportation Authority last year to a record $1.2 billion, a 20 percent rise over 2016, according to the Empire Center’s SeeThroughNY project.

The MTA notes that the bill was actually only $225 million above what it had budgeted for, and mainly blames the Summer of Hell. OT costs rose 26 percent to nearly three-quarters of a billion dollars at the Transit Authority as it launched major repairs to a system in crisis. That accounted for 62 percent of the MTA’s total OT bill.

The agency also says that Mayor de Blasio’s refusal to pay what it asked toward the $856 million subway action plan forced it to stretch out repairs and pay more OT: Without the city cash, it can’t hire more people to get vital work done.

It’s harder to justify the $175.4 million in OT expenses posted at the Long Island Rail Road, a jump of 10 percent over 2016. Yes, it had to handle problems at Penn Station — but nothing like the mess in the subways.

And while the average overtime payment was $13,629 at the Transit Authority, it was $22,701 at the LIRR — which also had the top OT earners, including 174 workers who raked in $100,000 or more above base pay. Nine collected over $200,000 in OT.

The root problem: The LIRR’s unions have extra power because they’re governed by federal, not state, law, which allows its workers to strike. (The feds keep it that way to cover up railroad-pension problems in other parts of the country.) That lets the overtime kings exploit work rules and seniority to cash in big.

In short, the MTA’s overtime problems are another sign of how much of the agency’s fate isn’t really in its own hands.