Back to school: Advanced internal-combustion engines are a sustainable solution for pupil transportation

As the new school year gets underway, the majority of students will rely on buses powered by internal-combustion engines, according to the Engine Technology Forum.

“Based on our estimates, over 85 percent of the approximately 540,000 school buses on the road today are powered by diesel engines,” said Allen Schaeffer, the executive director of the ETF. “Small percentages run on gasoline and propane. Nearly three-quarters of the diesel buses in operation today are the newest-generation models equipped with the most advanced emissions-control systems, including selective catalytic reduction (SCR) and particulate filters. Together, these technologies virtually eliminate emissions of nitrogen oxides and particulate matter.”

Today’s advanced diesel technology achieves near-zero emissions and has an unmatched combination of features that make it the technology of choice for school-bus fleets, according to ETF.

These include lower cost, greater reliability and durability, ease and access to fueling, nationwide parts and servicing networks, all-weather performance, suitability for irregular routes and contracted busing services, resale value and the ability to utilize renewable, low-carbon fuels.

“School districts recognize that there are many ways to boost their sustainability in addition to electrification,” Schaeffer said. “The most accessible and available option is by switching their fleet from diesel to biodiesel and renewable diesel fuels that reduce carbon and other emissions by 50 percent to 75 percent. These fuels can be used in any new or existing diesel bus and stored and dispensed without modifications to existing systems.”

The outlook for these fuels in the U.S. is growing dramatically, Schaeffer noted.

In 2024, the U.S. was on pace to surpass 5 billion gallons of biodiesel and renewable diesel consumption for the first time, according to Clean Fuels Alliance America.   

“Considerable public and philanthropic funding has driven the adoption of electric school buses over the last few years,” Schaeffer said. “According to the World Resources Institute, there are now more than 5,100 electric school buses serving students in the U.S. Electric buses offer some school-bus fleets another viable option for sustainably transporting students.”

Equally important in understanding sustainability choices is knowing the source of electricity used to charge the buses, Schaeffer said.

According to the Energy Information Administration, nationwide, 43.1 percent of electricity is generated from natural gas, 16.2 percent coal, 16.6 percent nuclear, and 21.4 percent renewable sources (wind, solar, hydro, biomass and geothermal).

“From the classroom to the bus depot, school districts are confronting a myriad of challenges with limited budgets,” Schaeffer said. “In many districts, shortages of qualified school-bus drivers are the main concern confronting fleet managers. Federal and other funding streams that facilitate electric buses and required infrastructure are uncertain or less available, complicating the adoption of these new technologies. That’s one reason we expect diesel-powered buses to remain the top choice for school districts nationwide for years to come.”

Getting the most bang from their transportation buck is the challenge facing every fleet manager, Schaeffer said.

“Regardless of the sustainability approach, whether electrification or use of renewable fuels and new diesel buses, retiring older buses and maximizing the number of students transported by newer, cleaner buses should be a top priority,” he added. “New buses offer many safety features that all students, not just a select few, should benefit from.”