Regulatory Tracker

Heavy-duty Truck “Glider Kit” Rule

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Why it Matters

More than 25% of the nation’s greenhouse gas emissions come from the transportation sector (chiefly cars and trucks), which also accounts for more than 70% of oil used in the United States. Medium- and heavy-duty vehicles cause about a quarter of the total transportation-related greenhouse gas emissions. A “glider” or “glider kit” is essentially an old heavy-duty truck engine installed into a new chassis, largely to avoid modern pollution control requirements. Many of the engines used in gliders generate, for example, nitrogen oxides (NOx) and particulate matter (PM) emissions that are 20 to 40 times higher than new engines. In fact, EPA estimated when it proposed new rules addressing gliders, that gliders accounted for just 2% of sales of new heavy-duty trucks but up to one half of all NOx and PM emissions from new trucks.

EPA’s vehicle emissions standards change as engine technology improves. Before 2016, EPA regulated gliders on the basis of the engine manufacture year: they could be marketed as new but only subject to lower emissions standards for older engines rather than up-to-date pollution standards.

In 2016, EPA and the National Highway Transportation Safety Administration (NHTSA) issued joint comprehensive regulations limiting the greenhouse gas emissions and fuel consumption of medium- and heavy-duty trucks. The emissions regulations apply pollution control standards to gliders based on the year the entire truck was manufactured, not just the engine. Including gliders in the regulations largely eliminates the incentive to use these much dirtier engines in newly manufactured trucks. These regulations are projected to reduce greenhouse gas emissions by nearly 200 million metric tons by 2050, and to significantly reduce NOx and PM emissions as well.


2011 EPA and NHTSA publish Phase 1 regulations, Greenhouse Gas Emissions Standards and Fuel Efficiency Standards for Medium- and Heavy-Duty Engines and Vehicles. All gliders are exempt from NHTSA’s Phase 1 fuel efficiency standards. Gliders manufactured by small businesses are exempted from EPA’s Phase 1 emissions requirements.

Nov. 14, 2011 Phase 1 regulations go into effect.

Feb. 18, 2014 President Obama directs EPA and NHTSA to develop Phase 2 standards.

July 13, 2015 EPA and NHTSA published a joint, proposed Phase 2 rule, “Greenhouse Gas Emissions and Fuel Efficiency Standards: Medium- and Heavy-Duty Engines and Vehicles; Phase 2.” Both agencies propose including gliders as regulated entities and sought comments related to that proposal. Many of the large truck manufacturing companies supported, and still support, these regulations. In particular, industry supports applying the up-to-date pollution standards to gliders, as the sale of gliders undercuts the manufacturers’ investment in better emissions control technologies.

Oct. 1, 2015 The comment period for the proposed rule closes, after being extended on Sep. 8, 2015.

Oct. 25, 2016 The agencies publish the final rule with an effective date of Dec. 27, 2016. EPA includes regulations for reducing CO2 emissions from tractor trailers and gliders and sets an annual manufacturing cap of 300 gliders per company. NHTSA affirms its safety authority over gliders but does not finalize fuel efficiency standards for gliders. The implementation date for EPA’s new emissions standards for gliders is Jan. 1, 2018.

Dec. 22, 2016 Truck Trailer Manufacturers Association, Inc. (TTMA) files a petition for review in the D.C. Circuit Court of Appeals challenging EPA and NHTSA rules, Truck Trailer Manufacturers v. EPA, et al., Docket No. 16-01430. TTMA argues that the agencies exceeded their statutory authority in promulgating the new rule which regulates tractor trailer emissions by setting aerodynamic equipment requirements. Specifically, TTMA asserted that trailers cannot be considered new vehicles under the Clean Air Act, and thus EPA does not have the authority to regulate them.

Dec. 26, 2016 Racing Enthusiasts and Suppliers coalition also files a petition for review in the D.C. Circuit, Racing Enthusiasts and Sup. v. EPA, et. al., Docket No. 16-1447. This case is consolidated with TTMA’s case.

Trump Era

Jan. 23, 2017 Seven states, the California Air Resources Board, and environmental groups join the lawsuit on behalf of EPA and NHTSA.

April 3, 2017 TTMA sends letters to NHTSA and EPA requesting that the agencies review, reconsider, and rescind the trailer standards.

April 20, 2017 EPA and NHTSA file a motion to delay the case in light of TTMA’s request to reconsider. TTMA partially opposes this motion because EPA has yet to finalize a decision to reconsider the rule.

May 8, 2017 The court puts the case on hold for 90 days, twice extending that period as EPA continues to review TTMA’s request to reconsider the rule.

Aug. 17, 2017 EPA and NHTSA respond to TTMA’s request and agree to reconsider the rule.

Sep. 25, 2017 TTMA submits a motion for a stay of the requirements for trailers, which would stop those standards from going into effect.

Oct. 12, 2017 EPA declares that it would take no position on TTMA’s motion for a stay. The state intervenors and environmental groups oppose the motion.

Oct. 27, 2017 The court orders that the case continue to be put on hold and that the requirements for trailers be suspended.

Nov. 16, 2017 EPA issues a proposed repeal of the emissions requirements for gliders. Comments to the proposed repeal are due on Jan. 5, 2018.

Jan. 22, 2018 EPA files a status report with the court, stating that the agency is developing a rule to revisit the trailer provisions of the rule.

Feb. 8, 2018 The California Air Resources Board adopts the 2016 Final Rule standards for glider kits produced in California.

Feb. 19, 2018 The president of Tennessee Tech University sends a letter to EPA Administrator Scott Pruitt requesting that the agency not use or reference a Tennessee Tech study, which found that glider engines and new engines produced similar amounts of emissions. The University is investigating the validity of the study, which was funded by one of the nation’s largest glider kit manufacturers, after experts questioned its methodology. Industry relied on the study in its request to EPA to reconsider the rule, and EPA referenced industry’s reliance on the study in the proposed repeal.

March 2018 Fourteen Republican members of Congress (four senators and 10 representatives) send letters to EPA Administrator Scott Pruitt asking the agency not to repeal the emissions standards for glider vehicles because it will undermine manufacturing industries in their home states.

July 6, 2018 The EPA announces that it will not enforce the annual cap of 300 gliders per manufacturer, at least through the end of 2019. EPA is considering formally delaying the glider manufacturing cap until December 2019 and working to repeal it in the meantime.

July 13, 2018 A coalition of 13 attorneys general submit a letter to the EPA, urging the Acting Administrator, Andrew Wheeler, to withdraw the Glider Announcement that suspends the manufacturing cap or change course and enforce the cap.

July 17, 2018 A coalition of environmental advocacy groups files an emergency motion in the U.S. Court of Appeals for the D.C. Circuit, asking the court to enforce the manufacturing cap or halt the EPA’s Glider Announcement. Both requests have the same outcome — the cap will go into effect for 2018, either by court enforcement or by the court halting the Glider Announcement.

July 18, 2018 The D.C. Circuit grants the emergency motion and issues an administrative stay, halting the EPA’s Glider Announcement of not enforcing the glider manufacturing cap. So, the cap will go into effect for 2018 while the court considers the issues raised in the motion.

July 19, 2018 A coalition of 16 state attorneys general file a lawsuit challenging the EPA’s Glider Announcement. The coalition includes the attorneys general of California, Delaware, Illinois, Maine, Maryland, Massachusetts, New Jersey, New York, New Mexico, North Carolina, Oregon, Pennsylvania, Rhode Island, Vermont, Washington, and the District of Columbia, as well as the California Air Resources Board, the Minnesota Pollution Control Agency, and the Pennsylvania Department of Environmental Protection.

July 26, 2018 Acting EPA Administrator Andrew Wheeler withdraws the Glider Announcement, meaning that EPA will enforce the annual manufacturing cap for gliders for 2018 and future years.

Aug. 21, 2018 The Assistant Administrator for Air and Radiation at EPA, Bill Wehrum, sends a letter to the Chairman of the House Science, Space and Technology Committee defending the agency’s emissions testing and findings on glider kit trucks.

Sep. 13, 2018 The House Subcommittee on Oversight and Subcommittee on Environment holds a hearing, “Examining the Underlying Science and Impacts of Glider Truck Regulations.”

Oct. 23, 2018 Tennessee Tech releases a letter stating that the university’s internal investigation of the controversial glider truck study found that the study’s field-testing procedures “were not sufficient to justify comparison with EPA emissions standards” and “the data does not support” the finding that glider trucks performed as well as certified engines.

July 31, 2019 EPA’s Office of Inspector General releases a report finding that the agency did not violate any standard EPA practices when it tested glider kits in 2017, but recommended revisions to the agency’s policy on accepting donated vehicles for testing. The report was produced in response to two congressional requests that raised concerns about EPA’s glider vehicle testing activities in 2017.

Dec. 5, 2019 EPA’s Office of Inspector General releases a report finding that the agency failed to develop required cost and benefit analyses and to assess air quality impacts on children’s health for the proposed Glider Repeal Rule. The report found that “The EPA did not comply with requirements of [Executive Orders] 12866 and 13045 when developing and issuing the proposed Glider Repeal Rule…According to EPA managers and officials, then-EPA Administrator Scott Pruitt directed that the Glider Repeal Rule be promulgated as quickly as possible… Pruitt directed the Office of Air and Radiation to develop the proposed rule without conducting the analyses required by the EOs. The lack of analyses caused the public to not be informed of the proposed rule’s benefits, costs, potential alternatives and impacts on children’s health during the public comment period.”

Sep. 29, 2020 The D.C. Circuit grants TTMA’s motion to stay the compliance dates for the NHTSA fuel economy regulations to the extent they apply to truck trailers. Truck Trailer Mfrs. v. EPA, No. 16-01430 (D.C. Cir.).