A 2017 study by the U.S. Environmental Protection Agency that found glider trucks emit more greenhouse gases than newer trucks is getting another look.

At the request of four Republican congressmen, the Office of Inspector General for the Environmental Protection Agency announced plans to conduct an audit of the agency’s 2017 study of glider kit trucks. Glider kits are a long-standing option for truck buyers that allows a new truck frame and body to be fitted with an older, refurbished powertrain – which has not been required to meet current EPA emissions standards.

While glider kits originally were designed to allow truck owners to refurbish wrecked vehicles, in recent years they gained popularity as a way for truck owners to avoid early-generation low-emissions engines that were plagued with maintenance problems and got poorer fuel economy. Opponents of glider kits saw this as a loophole that needed to be closed, and the GHG Phase 2 emissions/fuel economy regulations curtailed their use. Some glider kit makers, including Fitzgerald, challenged the Obama-era rules. Currently the EPA is still evaluating a proposal that would remove the glider kit provisions from the rules.

Two different studies have been cited by those on both sides of the issue, and both have come under fire for different reasons.

In a Sept. 4 letter to EPA’s Office of Air and Radiation, the Inspector General’s office said it will “examine the selection, acquisition and testing of glider vehicles at EPA’s National Vehicle and Fuel Emissions Laboratory as well as EPA’s planning for this testing.”

The audit is in response to questions raised in June by Rep. Greg Gianforte of Montana, chairman of the House Subcommittee on the Interior, Energy and Environment, who questioned the integrity of the EPA glider truck study. Gianforte was joined by three other Republican congressmen, including Reps. Bill Posey of Florida, Steve King of Iowa, and Brian Babin of Texas, who also wrote to the Inspector General requesting an audit of the EPA study.

The EPA study has been controversial since it was released last November, just days after the EPA’s administrator at the time, Scott Pruitt, proposed repealing a rule from the Obama Administration that limited the number of nonemission compliant gliders built by a manufacturer to 300 units per year. The rule was included in the EPA’s 2016 Phase 2 greenhouse gas emissions standards for heavy trucks. Pruitt was forced to resign from the EPA in the wake of scandals earlier this year, although the agency is still considering repealing the Obama-era rule limiting the number of annual glider kit production.

Adding to the furor is the fact that the Republican lawmakers requesting the audit seem to be suggesting Volvo North America rigged the study to produce an outcome in support of newer, emissions-compliant truck models.

The matter is further clouded by a competing study conducted by Tennessee Tech University and funded by Tennessee-based glider manufacturer Fitzgerald Gliders, which found that newer trucks “in some instances” emitted more harmful emissions into the air than glider kits. The Trump-era EPA has cited this study as a reason for rolling back the Obama-era standards limiting glider kit production. However, Tennessee Tech’s own faculty senate has condemned the study as biased. The school’s president, Phil Oldham, said last February that the school would launch an investigation into how the Fitzgerald-funded study was conducted to ensure that proper scientific and educational standards were followed.

While the EPA currently has no plans to audit the Tennessee Tech glider study’s findings, agency spokesperson Jennifer Kaplan stressed that this audit is not an investigation into allegations of misconduct.

In his letter to the EPA Inspector General, Gianforte claimed that EPA employees reached out to Volvo — which opposes repealing the glider rule — about obtaining glider kit test vehicles. Volvo agreed to work through its dealer network to obtain at least one glider kit for evaluation purposes.

John Mies, manager of corporate communications for Volvo Group North America, said in a statement, “Like most of the trucking industry, the Volvo Group for several years now has argued that the improper use of glider kits is bad for the environment and unfair to manufacturers who have invested in the latest environmental controls. All our communication and cooperation with the EPA on this issue has been an entirely appropriate part of a broad trucking industry advocacy effort. We did nothing improper.”