The Environmental Protection Agency wants to change how it classifies "glider vehicles" — heavy trucks that are built by pairing a new chassis with an old diesel engine and powertrain. The move would keep the EPA from imposing Clean Air Act emissions standards on the trucks.

To make a glider, companies typically combine a new truck body and cab with a salvaged powertrain. The vintage of the reused engine is important: Many of them date to before 2010, when the EPA tightened emissions standards for pollutants such as nitrogen oxide and particulate matter emitted by heavy duty diesel engines.

For years, usable powertrains had been salvaged from wrecked trucks to make glider vehicles that cost about 25 percent less than new trucks, the EPA says. But it was only after the recent enactment of new emissions restrictions that glider vehicles were "produced in any great number," the agency says.

A main player in the glider industry is Fitzgerald, which petitioned for the EPA rule change along with other companies. In proposing its reversal of course, the EPA cited their petition — including research from Tennessee Tech, which has ties to Fitzgerald. The EPA cited a study by the school that found glider vehicles would emit less than 12 percent of the total NOx and PM emissions for all heavy trucks on the road, rather than the 33 percent that had been claimed by the EPA under the Obama administration.

The EPA published its proposal in the Federal Register on Thursday, saying that its interpretation of the Clean Air Act has changed from the Obama administration to the Trump administration.

Specifically, the agency says its definitions of terms such as "new motor vehicle," "new motor vehicle engines," and "incomplete" new motor vehicles have changed in the Trump era — and that those terms shouldn't apply to glider trucks. In explaining the change, the EPA says that it's entitled to change positions under a new administration. It also says previous interpretations of the CAA were "incorrect."

From the agency:

"In proposing a new interpretation of the relevant statutory language, EPA now believes that its prior reading was not the best reading, and that the Agency failed to consider adequately the most important threshold consideration: i.e., whether or not Congress, in defining 'new motor vehicle' ... had a specific intent to include ... such a thing as a glider vehicle – a vehicle comprised both of new and previously owned components."

The EPA says it also no longer views glider kits as "incomplete" new motor vehicles, based on the idea that because "a glider kit lacks a powertrain, a glider kit does not explicitly meet the definition of 'motor vehicle.' "

In its rule proposal, the agency adds that it believes its current interpretation is "the most reasonable reading" of the law.

The agency has opened a comment period on the proposed change, running through Jan. 5. In addition, the EPA will hold a public hearing on the rule proposal on Monday, Dec. 4.

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