School Buses

Internal combustion engines power the vast majority of school buses in operation today, accounting for nearly 99% of the fleet. While new options and federal incentives are accelerating adoption of battery electric school buses, internal combustion technologies will continue to play a central role in pupil transportation for years to come.

Approximately 537,000 school buses transport more than 23.5 million students across the United States each day, traveling over 4.3 billion miles annually. These vehicles form the backbone of student transportation systems nationwide.

Internal combustion engines dominate this sector, with 99% of school buses powered by diesel, gasoline, propane, or natural gas. Diesel remains the leading technology, powering 87% of the fleet due to its energy efficiency, reliability, durability, range, and established fueling and maintenance infrastructure.

A significant portion of today’s diesel fleet has transitioned to newer, cleaner technologies. More than 72% of diesel school buses in operation are equipped with advanced diesel engines. These post-2010 engines, enabled by ultra-low sulfur diesel (ULSD) fuel and emissions control systems such as diesel particulate filters and selective catalytic reduction (SCR), achieve near-zero levels of particulate matter (PM), hydrocarbons (HC), and nitrogen oxide (NOx) emissions compared to older engines.

Gasoline, propane, and natural gas buses make up a smaller share of the fleet, providing additional internal combustion options for school districts based on local needs and fuel availability.

Decarbonization Options for School Buses

School districts across the country are working to reduce emissions and improve sustainability. A range of technologies and strategies are available, and no single solution fits every district. Decisions depend on factors such as route characteristics, climate, budget, and infrastructure.

Renewable Bio-based Diesel Fuels

Because diesel remains the dominant technology, one of the most immediately available strategies is the use of low-carbon renewable fuels such as biodiesel and renewable diesel. These fuels can be used in existing diesel buses without modifications to vehicles or fueling infrastructure and can reduce lifecycle carbon emissions by 50% to 86%, depending on feedstocks.

Electric Buses

Battery electric school buses are gaining momentum, supported by federal funding programs and policy incentives introduced in recent years. These vehicles produce zero tailpipe emissions, offering clear air quality benefits at the point of use.

At the same time, school districts must consider a range of operational factors when evaluating electric buses, including charging infrastructure requirements, utility upgrades, route range under varying weather conditions, and vehicle utilization patterns. In addition, total lifecycle emissions depend in part on how electricity is generated, with the current U.S. grid relying on a mix of natural gas, nuclear, renewables, and coal, according to the U.S. Energy Information Administration.

How Does Your State Compare?

How does your state rank in adopting the latest advanced diesel school bus technology? Increasing the share of newer, near-zero emission diesel buses can deliver immediate air quality benefits while fleets continue to transition toward lower-carbon solutions.

Explore state rankings