EPA 2027 NOx NPRM Expected by Late June, OEMs Say

EPA said it is currently working on revaluating the rule and is planning to propose a rule in the “spring of 2026.” (Pablo Martinez Monsivais/Associated Press)

LAS VEGAS — Truck and engine manufacturers expect the Environmental Protection Agency to release a draft of its long-awaited notice of proposed rulemaking on changes to nitrogen oxide tailpipe emissions for model-year 2027 by the end of June.

The agency is expected to leave in place a Biden-era requirement that NOx emissions for heavy-duty trucks fall to 35 milligrams per horsepower-hour from 200 mg/hp-hr. Beyond that, the trucking industry is still waiting for clarity on key details, including warranty requirements.

The Trump administration warned in 2025 that it could revisit the regulations, creating uncertainty alongside disruption from tariffs. Fleet managers responded by keeping equipment spending to a minimum.

An NPRM is a formal document issued by a federal agency that announces the intent to change, add or remove regulations. It outlines the proposal and invites public comment.

Retention of the current warranty length would be welcomed by fleets, as it likely would limit cost increases. Some OEMs told carriers at ACT Expo that potential price hikes could be cut in half if warranty terms remain unchanged.

David Hillman, International Motors vice president of integrated technology sales, told attendees at the 2026 Advanced Clean Transportation Expo he hears that the NPRM will retain the current five-year, 100,000-mile warranty for engine emissions systems. “Not a week goes by that me and my team don’t get asked, ‘What’s the pricing on this?’” Hillman said. “We don’t know. We don’t know the pricing yet today. But I don’t begrudge you if you want to ask.”

“What we don’t want to do is [establish a] price given the regulations on the books right now, and then have an NPRM come out that dramatically changes that and then everyone has to reshuffle,” he added.

Traton division International unveiled plans in January for an EPA 2027-compliant S13 engine. The S13 integrated powertrain was initially launched in August 2022.

Andrea Brown, Mack Trucks engine propulsion product management director, told reporters at the show that while the rumored June release was likely, it’s not certain.

EPA told Transport Topics it is currently working on revaluating the rule and is planning to propose a rule in the “spring of 2026.”

While manufacturers are not facing changes as extensive as those required when EPA updated emissions regulations in 2010, OEMs still need time to design and validate engines, Hillman said. That required lead time may explain why the 35-milligram NOx standard remained in place, even as other emissions-related developments — particularly in California — shifted.

To achieve the roughly 80% reduction in NOx emissions, engine manufacturer Cummins is using a belt-driven alternator to power aftertreatment heaters.

“We’re increasing the catalyst size instead of some other methods, but trying to simplify it as much as possible by using known designs and tailoring it,” said Andrea Lukas, director of product management for Cummins’ North American on-highway business.

The company opted for a larger selective catalytic reduction catalyst to achieve greater NOx reduction, requiring more surface area and substrate, Director of Customer Support Mark Ulrich told TT.

Cummins unveiled its EPA 2027-compatible X15 engine in March at the American Trucking Associations Technology & Maintenance Council Annual Meeting.

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The Cummins X15 engine is displayed in a tractor at TMC. (Seth Clevenger/Transport Topics)

Hillman said the industry is largely focused on emissions performance during the first few minutes of operation, particularly in cold conditions. “If you’ve got to drop down 80% of your emissions over the cycle, everyone is focusing on effectively the first five minutes of operation there,” he said.

International chose to use combustion heat to warm catalysts more quickly, one of two common approaches available to manufacturers.

Meanwhile, EPA’s slow pace in finalizing details could spur demand later in 2026, as carriers look to buy trucks ahead of the Jan. 1 compliance deadline. That so-called pre-buy could strain supply, Hillman said.

“The pre-buy is not expected to be as big for ’26 as it was, say, in 2009 or 2006, but it’s still expected to stress the industry,” he said.