Millennial commuters helped drive the Long Island Rail Road to its biggest ridership year in nearly seven decades, new LIRR figures show.

The 89.3 million people the railroad moved in 2016 set a modern record, and was 1.9 percent higher than its 2015 ridership of 87.6 million. The LIRR’s all-time ridership record was set in 1949, when the railroad carried 91.8 million customers.

And while the LIRR continues to serve largely the same region it did when it was founded 183 years ago, new data released Monday signal a major shift in who LIRR commuters are, what jobs they work and how they get there.

LIRR President Patrick Nowakowski said the railroad will use the ridership data in planning future service levels and infrastructure investments, such as the proposed construction of a third track between Floral Park and Hicksville.

“There is an intrinsic demand for reverse-peak travel to the Island that today is very difficult for the LIRR to accommodate as a two-track railroad,” Nowakowski said in a statement. “This data shows that if and when the Main Line is expanded to a third track, our reverse-commute service would fill an immediate unmet need.”

The LIRR released the findings of its Origin and Destination Study, which MTA director of special project development and planning William Wheeler described as a kind of “census” of LIRR riders.

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Using data compiled from 119,000 riders between 2012 and 2014, Wheeler said the survey confirmed “a phenomenon of a generation who has truly taken transit to heart as its primary mode of travel.”

While the majority of trips taken on the LIRR were still to get to and from jobs in Manhattan, about a third of all trips were for other purposes, including reverse commuters traveling east to jobs (6 percent) and nonwork travel to Manhattan (9 percent.)

The median age of LIRR commuters is 42.2, and the median household income is $144,251.

Wheeler said the surge of millennial transit riders represents “the demand that, in essence, we have been waiting for,” but added that it is also “challenging in many ways.”

Although 81 percent of commuters use the LIRR five days or more each week, Wheeler said the number of commuters traveling on just four days has grown substantially — signaling changes in the kinds of jobs held by commuters, including those in health care, entertainment and education.

Also changing is the stations from which LIRR customers commute. Ronkonkoma — long known as the LIRR’s busiest Long Island station — has been overtaken by Hicksville, where about 6,000 of the LIRR’s 98,000 morning commuters board a train each weekday.

The Metropolitan Transportation Authority also announced that it will vote Wednesday to officially expand sleep apnea testing to all train and bus operators, including those on the LIRR.

About 10 months after the MTA announced the plan, officials said Monday they are prepared to hire four different health care agencies to conduct sleep testing for its workers, including two agencies on Long Island. Testing has already been in place at Metro-North, the LIRR’s sister railroad, since 2015.

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Federal officials have said sleep apnea contributed to several train accidents in recent years, including the October crash of an NJ Transit train in Hoboken. Sen. Chuck Schumer (D-N.Y.), who has been briefed by National Transportation Safety Board investigators, has also said sleep apnea is suspected in the crash of an LIRR train in Brooklyn earlier this month. The cause of that accident, which injured more than 100 people, has not been determined.

With the move, MTA chairman Thomas Prendergast said the public transportation agency is “going further than any other” to prevent the risks of the sleep disorder.

CORRECTION: An earlier version of this story gave an incorrect number of riders the Long Island Rail Road carried in 2016.