The Port Authority is investigating how a New Jersey trash hauler with a checkered — and now deadly — safety history recently won half a million dollars in contracts from the agency, The Post has learned.

A tire from a Century Waste Services truck last week flew off and smashed the windshield of an NYPD steamfitter’s vehicle as he drove to work on the Gowanus Expressway in Brooklyn, killing him.

It soon surfaced that the Elizabeth garbage company had been cited by the feds for “loose and/or missing” wheel fasteners earlier this year — one of 74 times the company had been nailed for everything from worn tires to improperly maintained brakes since 2016.

The Port Authority told The Post that it will now zero in on Century’s recent safety record — and whether the company was appropriately vetted when it received recent contracts worth a combined $459,000.

“In light of the accident that occurred [last] week, the Port Authority’s independent Inspector General will investigate the recent safety record of Century Waste Services, and we will determine whether to keep doing business with the company,” agency spokesman Steve Coleman said in a statement.

“In addition, the Inspector General will review the vetting process of Century Waste Services that was undertaken by the Port Authority, and make recommendations as to whether there are any needed changes to our vetting process.”

One of the PA’s recent contracts with Century was awarded May 18 and began later that month. The second one was signed July 20 — and began the day of the deadly accident.

City records show that the Sanitation Department also has paid Century Waste $169,000 since 2014 to help with snow removal, most recently in 2017.

But “the Sanitation Department does not have a current, active contract with Century Waste Services,” a spokeswoman said. “DSNY checks emergency service vendors’ background for integrity, lawsuit or erroneous issues. CWS cleared this background check.”

Last week’s accident killed 64-year-old civilian Police Department worker Robert Martinez, who was driving a 2003 Chevrolet Tracker and who was headed into Manhattan when his vehicle was struck by the wheel of a 2009 Mack garbage truck.

No one has been charged in the incident, according to police.

“Our hearts go out to the family of the victim. This event was an unfortunate accident,” said Ara Chekmayan, a spokesman for Century Waste. “We are fully cooperating with the investigation of this tragic event.”

All told, Century Waste Services has been inspected 21 times over the past two years, according to records from the Federal Motor Carrier Safety Administration.

Two-thirds of those investigations — or 65 percent — resulted in the feds yanking a vehicle off the road until it could be made safe, according to the agency’s data.

That’s triple the industrywide average of 20.7 percent.