ETF testifies on advanced diesel technology, SCR systems at EPA hearing

The Engine Technology Forum delivered testimony July 29 to the U.S. EPA regarding proposed amendments affecting model-year 2027 and later heavy-duty highway engines and selective catalytic reduction (SCR) emissions control systems. 

In its testimony, ETF emphasized the industry’s confidence in advanced diesel engines equipped SCR and diesel exhaust fluid (DEF) technology, highlighting their proven ability to achieve near-zero emissions while delivering the performance, durability and fuel efficiency relied upon by 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 of 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 percent 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,” Schaeffer said.

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.

The impacts of these changes have yet to be realized by consumers. 

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 issues with emissions-control systems occur is an important consideration for both EPA and original-equipment manufacturers (OEMs).

ETF defers to its member companies as the parties best positioned to address how these proposed changes could affect their customers.

ETF’s comments highlighted that diesel engines remain the dominant power source for commercial transportation, accounting for 76 percent of all commercial vehicles in operation.

More importantly, the nation’s fleet continues to transition rapidly toward newer, cleaner technologies.

As of the end of 2025, approximately 67 percent 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 percent of diesel transit buses and 72 percent of diesel school buses now operate with advanced diesel technology equipped with SCR emissions-control systems.

Proven environmental, economic benefits

ETF-sponsored research by Auto Forecast Solutions found that between 2011 and 2030, advanced diesel engines are expected to:

• Reduce fuel consumption by 130 billion gallons.

• Eliminate 18 million tons of NOx emissions.

• Prevent 1 million tons of particulate-matter (PM) emissions.

• Reduce carbon-dioxide (CO2) emissions by approximately 1.3 billion tons.

SCR and DEF emissions-control technology has been a primary contributor to these clean-air gains, enabling manufacturers to optimize engine performance saving fleet operators, farmers and truckers thousands of dollars in fuel costs.

By retaining these ambitious standards, EPA demonstrates confidence in SCR and DEF emissions-control technologies that have already proven their effectiveness in real-world operation across millions of vehicles and equipment with countless miles and hours of service.  

To aid in the understanding about diesel emissions-control systems, ETF recently launched its SCR & DEF Policy and Technical Resource Center, which features  webinars, fact sheets and general information.

ETF will expand outreach efforts to policymakers and consumers, which will focus on the necessity for these systems and their measurable benefits to air quality, DEF handling and storage, performance benefits, increased fuel economy, as well as the importance of complying with the federal Clean Air Act.

“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,” Schaeffer said.