Advanced diesel and natural gas engines continue to make up the majority of the nation’s school transportation fleet, according to new analysis from the Engine Technology Forum (ETF), a nonprofit educational association.

ETF analyzed S&P Global Mobility TIPNet data on U.S. commercial vehicles in operation as of December 2025 and found that nearly three-quarters of diesel school buses in operation — 72% — were powered by model year 2010 and newer diesel engines. That marks a 5% increase since 2023.

According to ETF, newer diesel engines use advanced emissions-control technology designed to achieve near-zero emissions.

School Buses Continue Gradual Shift Toward Newer Technology

The analysis also found that electric vehicles remain a small portion of the school bus market, accounting for 1.1% of school buses in operation as of December 2025.

Allen Schaeffer, executive director of ETF, said replacing older vehicles with newer diesel and natural gas technology can provide emissions and fuel-efficiency benefits while alternative fuel adoption continues to evolve.

“As the timing and degree of transition to alternative vehicles and fuels remains in flux, the importance of continued investment in new technology internal combustion engine vehicles is vital to ensure continued progress on clean air and energy efficiency,” Schaeffer said.

ETF cited previous research estimating that newer-generation diesel technology in heavy-duty vehicles could significantly reduce carbon dioxide, particulate matter, nitrogen oxide emissions, and fuel consumption between 2011 and 2030.

Additional Emissions Reductions Expected

ETF said further emissions reductions are expected as new federal emissions regulations take effect beginning in 2027. According to the organization, the updated standards are expected to reduce nitrogen oxide emissions by more than 80% from current 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.”