NEW YORK (March 20, 2007) — Amid federal and state campaigns to limit school bus idling in this age of environmental concern, exactly what is the benefit of shutting down vehicles while waiting for students?

Results from a new EPA study appear to support the agency’s Clean School Bus USA program goal of reducing idling and demonstrates that reduced idling does lead to measurable reductions in diesel pollution and limits student exposure to harmful exhaust. Clean School Bus says school bus engines should be turned off as soon as possible after arriving at the loading or unloading zone, and the bus should not be restarted until the bus stops.

The EPA performed the study, "Characterization of the Fine Particle and Gaseous Emissions from School Bus Idling," in conjunction with its Office of Research & Development and the Region 2 office, which supports environmental health for New York, New Jersey Puerto Rico, the U.S. Virgin Islands and seven tribal nations in the St. Lawrence River and the Great Lakes areas, to quantify and compare the particulate matter and gaseous exhaust pollutants emitted from a half dozen selected diesel school buses used by the Katonah-Lewisboro School District in Cross River, N.Y., Half of the engines were shut down and then restarted, while the others were idled continuously.

“The study found that the emission ‘pulse’ measured as a school bus is restarted contains less carbon monoxide, oxides of nitrogen and other pollutants than if the school bus idled continuously over a 10-minute period,” said Matt Laurita, an environmental engineer with EPA Region 2. “The analysis also indicated that continuous idling for more than three minutes emitted more fine particle (soot) pollution than a restart.”

Of the six diesel Type D school buses tested with catalytic converters, four were equipped with 2002 model year Caterpillar 3126 engines, one had a 1997 Cat 3116 and one was a 2004 C7. The study simulated a 20-minute loading and unloading time during wintertime conditions with a hot restart and post-restart idling to record levels of particulate matter (PM), particulate polycyclic aromatic hydrocarbons (PAH), carbon monoxide (CO), total hydrocarbons (THC), oxides of nitrogen (NOx), and formaldehyde. The buses were not started until all students were seated. In these cases, the bus made an immediate, or restart and go, departure. The buses were then tested after being turned off for 10 minutes and then restarted for 10 minutes to warm the bus before the students boarded.

Finally, the buses were turned off, then restarted and put into operation. The study found that turning the engine off completely during loading/unloading is the best operating scenario, as there was a short but minor “burst” of emissions when the engine restarted. The emissions burst lasted less than five seconds for fine PM, CO and NOx.

Laurita added the EPA will hold a media event for the study in May.