Industry reaction to the Environmental Protection Agency’s updated 2027 nitrogen oxide proposed rule has been mixed, with several groups saying they hope the agency will reconsider some of the changes. 

The proposal was unveiled by EPA Administrator Lee Zeldin on July 9 in Washington.

It maintains the requirement that heavy-duty diesel engines reduce NOx emissions to 0.035 grams per horsepower-hour, but includes several key modifications: 

• Delays the expanded useful-life requirements until 2030.
• Maintains the five-year/100,000-mile emissions warranty.
• Replaces mandated DEF derates with warnings.
• Allows manufacturers to sell engines that do not meet the new standard by nonconformance penalties.

When making the announcement, Zeldin was joined by the heads of the American Trucking Associations, Daimler Truck North America, Paccar, and Cummins. They each expressed support for the proposal and the agency’s willingness to listen to the industry’s concerns as it seeks the balance between emissions reductions and economic realities.

However, even before the 45-day public comment period begins, numerous industry groups indicated they were not yet fully on board. For example, the Owner-Operator Independent Drivers Association said it would urge the EPA to maintain the 450,000-mile warranty coverage provision.

“The rule should ensure that truckers who purchase a new vehicle will not be constantly sidelined because of costly and repeated breakdowns that OOIDA members have historically experienced under new emissions regulations,” said Jay Grimes, OOIDA’s director of federal affairs. “Given these concerns, sensible warranty programs are critical for encouraging adoption of newer trucks.”

Grimes called the proposal a “missed opportunity to adequately correct the shortcomings” of the original rule, and that there are better solutions than cutting extended warranty periods. 

The Truck and Engine Manufacturers Association (EMA) said while it was still reviewing EPA’s updated proposal, it welcomes “the agency’s continued engagement on cost-effective and achievable requirements for manufacturers, trucking fleets, and equipment operators.”

The group stressed it is “critical” that the rule be finalized before the end of 2026 to provide manufacturers with the certainty necessary for compliance planning, market strategies, and product availability.

“That includes ensuring that regulatory mechanisms maintain the proven progress achieved through selective catalytic reduction (SCR) systems, while also reducing unnecessary vehicle or equipment downtime and avoiding operational impacts tied to regulatory inducements,” EMA said. 

NATSO and SIGMA, which represent truck stops and fuel marketers, expressed concern with the proposal to eliminate deratements. The groups said they supported previously issued guidance from the Trump administration aimed at resolving DEF performance concerns.

“Allowing ample time for existing guidance to penetrate the market will minimize unnecessary and punitive deratements for diesel vehicles while ensuring that selective catalytic reduction technology remains an essential part of every truck manufacturer’s investment and compliance strategy,” said David Fialkov, head of government affairs for both organizations. 

Fialkov added: “While the administration’s impatience is understandable, we believe it is counter-productive to prematurely disrupt that process when allowing it to proceed would negate the need for today’s DEF-related actions.”

Michael Berube, CEO of the clean technology non-profit CalStart, said the proposal could create industry uncertainty and confusion.

“Weakening the durability, warranty, and inducement provisions that support real-world performance could jeopardize long-term emissions reductions, increase danger to public health, and undermine confidence in the technologies needed to deliver cleaner freight today,” he said. 

Similarly, the Environmental Defense League said on its website ahead of Zeldin’s announcement that the proposal would result “in more pollution, health harms, and higher costs.”