The research the Environmental Protection Agency (EPA) cited in proposing to roll back a major truck pollution rule was “not accurate,” the university that conducted the study has concluded.

Tennessee Tech University’s conclusions, outlined in a letter Tuesday to the EPA, came after an academic review of the controversial research into the emissions of “glider” trucks.

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The heavy-duty trucks use new bodies and remanufactured, older engines that do not meet current EPA regulations. Environmentalists call them "super-polluting" trucks, citing research showing far higher emissions compared to new vehicles.

Philip Oldham, Tennessee Tech’s president, wrote last year that university research found that glider trucks “performed equally as well and in some instances out-performed the [original manufacturer] engines,” despite not being certified to current standards for pollutants like particulate matter and nitrogen oxides.

The research was funded by Fitzgerald Glider Kits, one of the country’s biggest glider makers.

Then-EPA Administrator Scott Pruitt Edward (Scott) Scott PruittJuan Williams: Swamp creature at the White House Science protections must be enforceable Conspicuous by their absence from the Republican Convention MORE cited the research in a proposal to repeal an Obama-era regulation from 2016 that would have limited the number of glider trucks that each company can sell per year.

That prompted Tennessee Tech’s Faculty Senate to seek a full academic review of the research.

“The university has concluded its internal investigation and has found that certain conclusions reported in the June 2017 letter were not accurate,” Trudy Harper, vice chairman of Tennessee Tech’s board of trustees, wrote in the letter sent to the EPA, Fitzgerald and Rep. Diane Black Diane Lynn BlackBottom line Overnight Health Care: Anti-abortion Democrats take heat from party | More states sue Purdue over opioid epidemic | 1 in 4 in poll say high costs led them to skip medical care Lamar Alexander's exit marks end of an era in evolving Tennessee MORE (R-Tenn.), who helped bring the research to the EPA’s attention.

Harper said the research methods Tennessee Tech used were not sufficient to support Oldham’s “equally as well” conclusion and that the data gathered by researchers do not support the claim.

She went on to say that the research “was methodologically sound,” but only for the stated purpose of establishing baseline pollution levels for Fitzgerald’s trucks and for newly manufactured engines. Harper expressed “regret” for the incident.

The EPA didn’t immediately respond to a request for comment on the letter.

Fitzgerald stands by the research and said the letter supports the company’s position.

“Contrary to the rank speculation from various groups, including self-interested trade associations and even people associated with Tennessee Tech, the results and the underlying data are valid and worthy of consideration,” said Jon Toomey, the company’s lobbyist. “The letter vindicates the study and the results speak for themselves.”

Toomey pointed specifically to the part of the letter saying the study was “methodologically sound” and “the methods, methodology, and measurements used were appropriate.”

Research conducted last year by EPA staff found that glider trucks emitted up to 40 times more pollution than comparable new trucks. But the EPA’s inspector general is investigating that research after Republican lawmakers said it may have been unduly influenced by lobbyists for new truck makers.

Glider trucks have become increasingly popular among small companies and individual truck drivers. They are considerably cheaper than completely new trucks, largely because they do not have new pollution control technology that was mandated starting in 2010.

Pruitt resigned in July amid numerous spending and ethics scandals. But on his last day, he wrote a memo declaring that the EPA would not enforce the cap on glider truck sales.

Acting Administrator Andrew Wheeler reversed that memo shortly after a federal court told the EPA to temporarily put it on hold.

Updated at 12:26 p.m.