California Air Resources Board

CARB aims to reduce children's exposure to harmful pollutants through regulatory requirements and incentive funding for new, cleaner school buses.

Particulate Matter Affects Children’s Health

The Children's Health Study, initiated in 1992, confirmed that exposure to high concentrations of particulate matter (PM) reduces lung development, has immediate adverse health effects, and with continued exposure, has lasting adverse health effects later in life. The Children's School Bus Exposure Study, conducted in 2003, further demonstrated that the school bus's own exhaust greatly increases children’s exposure, and the oldest buses have the highest rates of in-vehicle exposure. CARB is committed to prioritizing the most sensitive population groups and aims to reduce health risks through regulatory action and incentive programs for new clean technology.

CARB's Regulations Reduce Children's Exposure

CARB has taken several actions to reduce children’s exposure to vehicle-related pollutants during their school bus trips. Under the Truck and Bus Regulation, all school buses are required to have a particulate matter exhaust filter; either original manufacturer equipment or retrofit, or they must operate less than one thousand miles per calendar year. School buses of any fuel type are restricted from school bus idling at or near public or private schools, drivers are required to turn off engines immediately upon arrival at a school, and restart no more than thirty seconds before departure. Finally, school bus fleets must regularly test for excessive smoke.

CARB and Local Air Districts Continue to Invest in School Buses

Along with regulatory requirements, financial incentives are a major part of CARB’s efforts to ensure clean school buses are operating at our schools and in our neighborhoods. By providing funding that supports some or all of the cost of a new, clean technology vehicle, incentives help to drive the development of newer and cleaner technologies by speeding up their adoption by school bus fleet owners.

CARB has been working to provide financial incentives for school districts to replace older diesel-fueled school buses for nearly twenty years, starting with the Lower-Emission School Bus Program in 2001. CARB staff, in coordination with the local air districts and the California Energy Commission, developed guidelines that set the criteria for the program for school bus replacements and retrofits with the goal of reducing children’s exposure to harmful diesel exhaust.

As a result of CARB's efforts and those of the local air districts and school districts, staff estimate that most older diesel-fueled school buses have retrofit PM filters installed. Diesel PM filters became standard equipment from the manufacturer starting with approximately the 2006 school bus model year (2007 engine model year), so newer diesel buses already control a significant portion of their PM emissions without retrofit devices. Because most of the diesel school bus fleet is already equipped with PM filters, retrofits are no longer a priority for funding. Instead, funding must focus on school bus replacement.

Replacing older, more polluting school buses with newer, cleaner school buses in California is an important action to improve air quality overall and especially to protect the health of sensitive populations, like our children.

School Bus Cleanup is a Priority

Reducing PM emissions and near-source exposure is a priority, particularly because studies have shown that PM has immediate and long-lasting adverse human health effects, especially for sensitive populations such as children. The buses’ own exhaust exposes children riding in diesel school buses to these PM emissions, and the oldest, dirtiest school buses have the highest rates of in-vehicle exposure. Therefore, school bus replacement rightfully remains a priority to CARB.