ICEs continue to dominate in U.S. truck and bus fleets

99.9% of commercial vehicles still powered by internal combustion engines

According to an Engine Technology Forum analysis, gasoline, diesel, natural gas and propane remain the primary fuel and technology choices for U.S. commercial trucks, transit and school buses. (Photo: KHL Staff)

The U.S. commercial truck market in 2023 experienced substantial growth and is up 14% year-over-year, according to S&P Global Mobility. Its latest report indicates more than 1.6M new vehicles in the Class 1-8 GVW were registered in 2023.

Yet, despite the growing number of new additions on U.S. roads and highways, traditional power system technology continues to dominate within commercial vehicle fleets. According to an analysis by the Engine Technology Forum (ETF) of S&P Global Mobility TIPNet data* (as of December 2023), gasoline, diesel, natural gas and propane remain the primary fuel and technology choices for U.S. commercial trucks, transit and school buses, with 99.9% powered by internal combustion engines (ICEs). Diesel made up the lion’s share at 76%, followed by gasoline at 22%, then natural gas and propane.

Navistar International truck chassis Advanced technology near-zero emissions diesels saw significant growth in 2023, increasing by 4%. (Photo: KHL Staff)

Emerging zero-emissions technologies, including battery-electric and fuel cell electric vehicles (EVs), made up a small fraction of the U.S. commercial vehicle fleet in 2023, ETF stated. Among the population studied, transit buses had the largest portion of EVs at 7.8%, followed by school buses at just 0.4%. Electric-powered commercial trucks (Classes 3-8) account for over 20,000 units, while battery-electric school buses account for about 2,000 units.

Overall, battery-electric or fuel cell-powered vehicles make up 0.1% of the commercial truck population. California leads all states in EV adoption in commercial trucks, non-school buses (transit, inter-city buses) and school buses, said ETF. For commercial trucks alone, the state accounts for more than 25% of all EV commercial trucks in operation, followed by Pennsylvania, Washington, New York and Massachusetts.

Advanced technology diesels

Advanced technology near-zero emissions diesels saw significant growth in 2023, increasing by 4%. Of the commercial diesel trucks on the road (Classes 3-8), 61% now fall within the 2010 and newer model year (2010 + MY), meaning they are equipped with the latest emission controls that achieve the near-zero tailpipe emissions standards established by the U.S Environmental Protection Agency. California saw the fastest year-over-year growth in advanced technology diesel vehicles in operation (+13.3%).

ETF’s analysis indicated that 82% of Class 8 diesel trucks in operation are now advanced generation (2010 +MY) technology. Indiana leads the nation for diesel trucks, followed by the District of Columbia (72.8%), Pennsylvania (72.5%), Illinois (68.9%) and Oklahoma (68,8%). (The full ranking of states can be found at

“As more of the nation’s trucking fleet adopts the latest generation of advanced diesel and natural gas technology, communities are experiencing cleaner air and lower greenhouse gas emissions. And truckers save on their fuel expenses, too,” said Allen Schaeffer, executive director of ETF, a not-for-profit educational association.

He noted that roughly two-thirds of all commercial trucks in operation are equipped with advanced emissions control equipment that provides visibility into their contribution toward key states’ clean air and climate goals as well as the potential to do more with accelerating fleet turnover.

Source: Engine Technology Forum

Schaeffer cited previous research showing the climate, fuel savings and clean air impacts of 2010 +MY Classes 3-8 heavy-duty trucks equipped with advanced diesels. From 2010 to 2030, this generation of diesels is projected to:

  • Prevent approximately 1.3 billion tons of carbon dioxide emissions,
  • Save 130 billion gallons of fuel,
  • And yield a cumulative savings of 1 million tons of particulate matter and 18 million tons of nitrogen oxide emissions.

“These benefits will be even greater once new emission regulations are implemented for new vehicles starting in 2027,” Schaeffer added.

Renewable diesel

Renewable diesel is playing an important role in the trucking industry’s efforts toward decarbonization, as well. In 2023, more than 2.8 billion gallons of renewable diesel and 1.9 billion gallons of biodiesel were consumed, ETF cited, and renewable diesel fuel production capacity is estimated to reach 5.9 billion gal/y by the end of 2025.

In addition, more than 79% of the natural gas (CNG) used in transportation was renewable natural gas (RNG), the Transport Project reported. Data from the California Air Resources Board showed that, in California, Bio-CNG/RNG achieved an annual average carbon intensity score of -126.42 grams of CO2 equivalent/Mega Joule (gCO2e/MJ) for 2023 – the lowest carbon intensity score of any clean fuel option.

“While traditional petroleum-based fuels still dominate the vehicle sectors, the role of renewable fuels is growing,” Schaeffer said. “It’s especially important given the opportunity to deliver significant carbon and other emissions reductions across millions of internal combustion vehicles in operation.”

ETF publishes white paper on bio-based diesel fuel Developed with Transport Energy Strategies, paper addresses emissions benefits of renewable bio-based fuels

More ICE investment needed

Schaeffer said the timing and degree of transition to alternative vehicles and fuels remains in flux, making continued investment in new technology ICE vehicles vital to ensure continued progress toward clean air and climate commitments.

“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,” he pointed out.

Continued improvements for ICEs in the form of even “nearer-to-zero” emissions and lower fuel consumption are on the horizon, per ETF, with engine and vehicle manufacturers working to meet the most recent emissions regulations for both light- and heavy- duty vehicles. Advanced diesel trucks are capable of delivering the vast majority of clean air and greenhouse gas reduction benefits in the near term, ETF stated, with zero-emission vehicles expected to play a greater role in the later years of phase 3 rule implementation 2027-2032.

“While battery-electric and hydrogen options develop, along with their fueling networks, internal combustion engines are expected to dominate our goods movement and public transport sectors for decades to come,” Schaeffer said. “That’s why continued innovation, having the newest generation of these vehicles in place and expanding our use of renewable fuels will ensure continued progress as well as lower burden of greenhouse gas emissions reduction in the future.”

Additional ETF Findings
  • The newest generation advanced diesel trucks (2010 + MY) outnumber electric trucks (any model year) by 367:1.
  • For every electric Class 8 truck in operation (any model year), there are 240 new generation (2010+MY) advanced technology diesel trucks.
  • For every electric transit bus in operation (any model year), there are more than five new generation (2010+MY) advanced technology diesel buses.
  • For every electric school bus in operation (any model year), there are 155 new generation (2010+MY) advanced technology diesel buses.

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