EarthTalk: The Environmental Hazards of School Buses

Dear EarthTalk: Are my kids breathing in dangerous exhaust fumes by riding the school bus?-- Molly Schink, Winnetka, IL

Over 24 million children ride the bus to school every day and as a result are regularly exposed to harmful diesel exhaust emissions. Major components of diesel exhaust include carbon monoxide, sulphur dioxide, formaldehyde and tiny soot particles that carry substances called polynuclear aromatic hydrocarbons.

The U.S. Environmental Protection Agency (EPA) classifies diesel emissions as a "likely carcinogen." Diesel emissions are estimated to be responsible for 70 percent of the cancer risk arising from air pollution, according to the California Air Resources Board. Dangers from diesel exhaust can range from respiratory illnesses including asthma and bronchitis to lung cancer and heart disease.

Children are more vulnerable to the effects of diesel exhaust than adults because they breathe more quickly and take more air into their developing lungs. And on average, school children who ride the bus spend an average of 90 minutes each weekday in transit.

The EPA estimates that approximately 390,000 diesel school buses are on the road in the U.S. today. A third of these were made before 1990 when stricter emissions guidelines were first enforced. According to the National Resources Defense Council (NRDC), a child riding inside a school bus may be exposed to as much as four times the amount of toxic diesel fumes as someone riding in a car directly ahead of it.

Recently, the EPA pledged more than $1 million to a partnership called the Northeast Diesel Collaborative, which is comprised of eight different public and private entities working together to improve emissions on thousands of school buses throughout the northeastern U.S. Recipient groups are using the money primarily to reduce emissions on older buses by installing advanced pollution controls.

Retrofitting old buses with such controls involves installing emissions reducing filters. Diesel particulate filters, which cost around $700 each, can cut tailpipe emissions by a whopping 85 percent. And "closed crankcase filtration systems," which are installed under the hood and filter the discharges that come directly from the engine's crankcase vent, can cut engine soot by nearly 90 percent at a cost of around $7,500 each. Buses can be retrofitted with one or both filters.

Nationwide a number of school bus emission-reduction programs are underway with the help of the EPA's Clean School Bus USA program. In addition to retrofit projects the program seeks to replace older buses with new less polluting buses and encourage unnecessary school bus idling.

Concerned parents can help reduce their children's expose to diesel emissions from school buses by advocating at town and boards of education meetings for the use of new or retrofitted school buses. Also, bus windows should remain open when weather allows, and children are safer sitting nearer the front of the bus, as exhaust tends to accumulate in the back.

CONTACTS: EPA Clean School Bus USA; Northeast Diesel Collaborative; NRDC.

GOT AN ENVIRONMENTAL QUESTION? Send it to: EarthTalk, c/o E/The Environmental Magazine, P.O. Box 5098, Westport, CT 06881; submit it at:, or e-mail: Read past columns at:

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