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Administrative Law

D.C. Circuit Concludes Trailers Are Not "Motor Vehicles"

A partially divided panel concludes the Environmental Protection Agency may not regulate trailers as “motor vehicles.”


Law students are often asked to consider what constitutes a "vehicle," as in what sorts of things are covered by a law prohibiting "Vehicles in the Park." Today, the U.S. Court of Appeals for the D.C. Circuit resolved a somewhat similar question in reviewing a recent Environmental Protection Agency regulation.

In Truck Trailer Manufacturer Association v. Environmental Protection Agency, a partially divided panel considered whether trailers can be regulated as "motor vehicles" under federal law. In the view of the court, the tractors pulling trailers may constitute vehicles, but the trailers themselves are not.

Judge Walker wrote the opinion for the court, joined by Judge Katsas. His opinion begins:

In 2016, the Environmental Protection Agency issued a rule for trailers pulled by tractors based on a statute enabling the EPA to regulate "motor vehicles." In that same rule, the National Highway Traffic Safety Administration issued fuel efficiency standards for trailers based on a statute enabling NHTSA to regulate "commercial medium-duty or heavy-duty on-highway vehicles."

Trailers, however, have no motor. They are therefore not "motor vehicles." Nor are they "vehicles" when that term is used in the context of a vehicle's fuel economy, since motorless vehicles use no fuel.

We therefore grant the petition and vacate all portions of the rule that apply to trailers.

In addressing the relevant statutory text, Judge Walker writes:

The Act defines "motor vehicle" to exclude anything that does not propel itself. Id. § 7550(2). For the purposes of § 202, a "motor vehicle" is "any self-propelled vehicle designed for transporting persons or property on a street or highway." Id. (emphases added).

Because trailers are not "self-propelled," they are not motor vehicles under § 202. Therefore, the EPA cannot rely on §202 to regulate trailers' effects on greenhouse gas emissions.

The court also considered whether NHTSA could regulate trailers for purposes of federal fuel economy regulations, again rejecting the agency's claim of authority.

Because a trailer uses no fuel, it doesn't have fuel economy. And in the statutory context of § 32902, nothing is a vehicle unless it has fuel economy — a measure of miles traveled per gallon of fuel used.

NHTSA therefore lacked the authority to regulate trailers.

Judge Millett wrote separately, concurring in the judgment in part and dissenting in part. Here is a summary of her differences with the majority:

Because the trailers are tractor-propelled rather than self- propelled, I agree with the majority opinion's judgment that the Clean Air Act's text precludes the particular EPA regulations at issue here. I further agree with the majority opinion that, in seeking to reduce emissions, the EPA could instead regulate the tractors, including the types of trailers they are allowed to pull. Majority Op. 19 ("To be sure, NHTSA can regulate tractors based on the trailers they pull, as can the EPA."); see also Oral Arg. Tr. 10:16–11:1 (Association counsel answering "probably, yes" when asked if the EPA could "pass a regulation that says tractors are banned * * * from traveling on roads and highways if they're pulling loads that cause the tractor's emissions to increase by XX amount"). And nothing in today's decision forecloses the EPA from regulating the assembler of the tractor-trailer to ensure that the assembled tractor-trailers meet specified emission standards. See Oral Arg. Tr. 9:16–17 (Association counsel explaining that the EPA "definitely can regulate an assembler" that connects a tractor and a trailer).

But when it comes to the question of NHTSA's authority to issue its separate fuel economy regulations, I part ways with the majority opinion. NHTSA acted under a provision of the Energy Independence and Security Act of 2007 ("Energy Independence Act") that directed NHTSA to establish fuel efficiency standards for commercial medium- and heavy-duty "on-highway vehicles[.]" 49 U.S.C. § 32902(k)(2). Unlike the Clean Air Act, the Energy Independence Act contains no definition of the term "vehicle" other than regulating it in its on-highway operation and status. Given that focal point, NHTSA quite reasonably applied a long-established definition of vehicles that includes commercial trailers. The majority opinion's view that NHTSA's interpretation somehow runs afoul of "plain" non-existent text does not stand up.

Expect this case to be a new addition to Legislation & Regulation syllabi in law schools nationwide.