The Engine Technology Forum (ETF) has submitted testimony to the US Environmental Protection Agency (EPA) on proposed amendments affecting model year 2027 and later heavy-duty engines and selective catalytic reduction (SCR) systems. In its testimony, the organization “emphasized the industry’s confidence” in modern diesel engines equipped with SCR and diesel exhaust fluid (DEF) technology, and highlighted their “proven ability” to achieve near-zero emissions while maintaining the performance, durability and fuel efficiency required for commercial trucking, construction and other essential industries.
“Advanced diesel technology is a remarkable environmental and engineering success story that continues to evolve and improve,” said Allen Schaeffer, executive director at the ETF. “The facts are clear: today’s advanced diesel engines equipped with SCR systems and DEF are achieving near-zero emissions while delivering substantial fuel savings, outstanding performance and the reliability demanded by the industries that keep America moving.”
EPA’s decision to retain the stringent 2027 nitrogen oxide (NOx) standard means that next-generation heavy-duty truck engines will achieve more than an 80% reduction in NOx emissions compared with today’s technology.
“While SCR and DEF remain the gold standard for enabling diesel engines to meet EPA’s 2027 heavy-duty emissions standards, some truck and equipment operators have experienced legitimate operational challenges with previous generations of emissions control technology,” said Schaeffer.
To address these issues, truck, engine and equipment manufacturers are actively implementing EPA’s guidance, making adjustments to SCR and DEF systems on existing equipment where feasible and integrating the guidance into new products while evaluating EPA’s newly proposed approach.
EPA’s proposal presents a significant departure from its current approach to emissions compliance regarding engine derating and other provisions of the proposed rule. Addressing the end-user experience when emissions control system issues occur is an important consideration for both EPA and OEMs, the ETF said, adding that it defers to its member companies as the parties best positioned to address how these proposed changes could affect their customers.
ETF said that its comments highlighted that diesel engines remain the dominant power source for commercial transportation, accounting for 76% of all commercial vehicles in operation. And that, more importantly, the nation’s fleet continues to transition rapidly toward newer, cleaner technologies.
As of the end of 2025, approximately 67% of commercial diesel vehicles in operation were model year 2010 or newer and equipped with advanced emissions control systems. Nearly two-thirds of Class 8 trucks, 63% of diesel transit buses, and 72% of diesel school buses now operate with advanced diesel technology equipped with SCR emissions control systems.
Proven environmental and economic benefits
The Engine Technology Forum cited research by Auto Forecast Solutions that estimates that between 2011 and 20230 advanced diesel engines could reduce fuel consumption by 130 billion gallons and avoid approximately 1.3 billion tons of CO₂ emissions, while also reducing NOx and particulate emissions. The organization said SCR and DEF emissions control technologies have been a major contributor to these reductions.
To support understanding of diesel emissions control systems, ETF has launched the SCR & DEF Policy and Technical Resource Center featuring webinars, fact sheets and technical information. According to the organization, the resource is intended to provide guidance on SCR and DEF technology, emissions compliance, DEF handling and storage, fuel efficiency and air quality benefits.
“ETF remains committed to providing factual, technology-focused information, supporting innovation and helping ensure that advanced diesel engines continue to deliver both environmental benefits and operational value,” said Schaeffer.
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