WASHINGTON, Nov 12 (Reuters) - A U.S. appeals court on Friday tossed out greenhouse gas emissions rules for heavy-duty truck trailers, ruling two government agencies had exceeded their authority. The Environmental Protection Agency (EPA) and National Highway Traffic Safety Administration (NHTSA) in 2016 set rules for the first time requiring trailer manufacturers to adopt fuel-saving technologies like side skirts and automatic tire pressure systems. An industry group challenged the rule, which was put on hold by the court pending the review.The administration of then-President Barack Obama said it was important to regulate the fuel efficiency of the trailer portion of commercial tractor-trailers "because large tractor-trailers account for 60% of the fuel consumption and carbon dioxide emissions from heavy-duty vehicles." The court ruled that if it allowed the trailer regulations, then "NHTSA could regulate bike racks, rooftop cargo carriers, or anything similar that would impact the fuel efficiency of a vehicle." The court added: "NHTSA can regulate tractors based on the trailers they pull, as can the EPA. But neither NHTSA nor the EPA can regulate trailers themselves."The EPA said in 2016 as much as one-third of potential reductions in tractor-trailer emissions could be achieved through regulation of the trailer’s equipment and design alone. The EPA and NHTSA did not immediately comment.The Truck Trailer Manufacturers Association (TTMA), which had sued to block the rules, said it was still reading the ruling and did not immediately comment. The group had argued that the rules were improper because trailers do not consume fuel, as they are not self-propelled. TTMA said earlier its members, which manufacture 90% of U.S. truck trailers, would incur "unrecoverable compliance costs," including from reconfiguring assembly lines.