More of America’s truck, bus fleets powered by advanced diesel engines than ever before

More than two-thirds of all commercial diesel trucks and buses are now powered by the latest generation of advanced diesel technology.

Diesel, gasoline, natural gas and propane continue to be the primary fuel and technology choices for America’s commercial trucks, transit and school buses, with the share of advanced technology near-zero emissions diesel vehicles increasing 4 percent since 2023, according to the Engine Technology Forum, a not-for-profit educational association.

ETF’s analysis of S&P Global Mobility TIPNet data on U.S. commercial vehicles in operation as of December 2025 found that more than 98 percent of the nation’s commercial vehicles—from small white-box delivery trucks up to the largest 18-wheelers—are powered by internal-combustion engines (ICE).

Diesel makes up the largest share at 76 percent, followed by gasoline at 23 percent, then natural gas at 0.5 percent.

Nearly two-thirds of all diesel transit buses (63 percent) and nearly three-quarters of all diesel school buses (72 percent) in operation were powered by advanced diesel engines (model year 2010 and newer) at the end of 2025, increasing 8 percent and 5 percent, respectively, since 2023.

As of December 2025, 67 percent of all commercial diesel vehicles on the road were model year 2010 and newer (MY 2010+), a 6 percent increase from 2023.

From 2020 to 2025, the share of Class 3-8 diesel vehicles in operation that are MY 2010+ increased from about 50 percent to over two-thirds.

These vehicles feature advanced emissions controls that achieve near-zero emissions.

Arizona has the fastest growing population of MY 2010+ Class 8 diesel trucks in operation, with a nearly 23 percent increase compared to 2023.

“As more of the nation’s truck and bus fleets adopt the latest generation of advanced diesel and natural-gas technology, communities are experiencing cleaner air and fleets save on their fuel expenses too,” said ETF Executive Director Allen Schaeffer. “Previous research showed the significant climate, fuel savings and clean-air impacts in the U.S. of the newer generation (MY 2010+) of advanced diesel in Class 3-8 heavy-duty vehicles. From 2011 through 2030, this generation of diesels will save approximately 1.3 billion tons of carbon-dioxide emissions and 130 billion gallons of fuel, while yielding cumulative savings of 1 million tons of particulate matter and 18 million tons of nitrogen oxide. These benefits will be even greater once new emissions regulations are implemented for new vehicles starting in 2027.”

Emerging zero-emissions technologies, including battery-electric and fuel-cell electric vehicles, presently make up a small fraction of the commercial-vehicle fleet.

In this analysis, the largest portions of vehicles powered by electricity in the studied population are transit buses (8.6 percent EV), followed by school buses (1.1 percent EV).

“As the timing and degree of transition to alternative vehicles and fuels remains in flux, the importance of continued investment in new technology ICE vehicles is vital to ensure continued progress on clean air and energy efficiency,” Schaeffer said. “Replacing older vehicles with new advanced ICE technology delivers substantial benefits. It would take more than 60 of the current-generation diesels to equal the emissions of a single heavy-duty diesel truck built in the 1990s.”

California leads all states in the adoption of EV technology in commercial trucks, nonschool buses (transit and intercity buses), and school buses.

For commercial vehicles (Class 3-8) alone, California accounts for more than 21 percent of all EVs in operation, followed by Michigan, Florida, Maryland and Illinois.

Continued improvements in ICE engines in the form of even nearer-to-zero emissions are on the horizon.

Engine and vehicle manufacturers are working to meet the most recent emissions regulations that begin in 2027.

These are expected to reduce nitrogen-oxide emissions by over 80 percent from today’s levels.

“While the scale and speed of alternative-fuel adoption by the commercial-vehicle sector is uncertain, internal-combustion engines demonstrate continuous improvement and are expected to dominate our goods movement and public transport sectors for decades to come,” Schaeffer said. “That’s why having more of the newest generation of these vehicles in operation will deliver the greatest benefits for all.”