NRDC: No Breathing in the Aisles: Diesel Exhaust Inside School ...

CHAPTER 1
EXHAUST EXPOSURES
ON CALIFORNIA
SCHOOL BUSES–
STUDY RESULTS
Diesel exhaust is a hazardous substance that has been linked to cancer and respiratory
disease, particularly after repeated exposure over time. Many children and adults
report that they notice the unpleasant smell of diesel exhaust when riding in school
buses. Some people report that the smell is stronger in the back of the bus, or when the bus is
idling at a traffic light or bus stop, suggesting a direct effect of emissions from the bus. This
study was designed to evaluate a child’s exposure to diesel exhaust on school buses, and to
determine whether riding diesel buses to school for years may pose a health risk to young
children. In particular, this study compares the diesel exhaust in the air inside school buses
with the diesel exhaust in the air inside passenger cars driving immediately in front of these
same school buses.
STUDY DESIGN
A team of researchers from NRDC and the U.C. Berkeley School of Public Health designed
a study to test levels of diesel exhaust inside school buses. NRDC and U.C. Berkeley rented
school buses that currently are used to transport children every day in the Los Angeles area.
Each bus drove an actual elementary school bus route of about 45 minutes duration for 4–6
repetitions over a period of five hours. The researchers used equipment to sample continuously
the air inside the buses for evidence of diesel exhaust and also tested for comparison
outside the bus and in a passenger car traveling ahead of the bus. The bus routes included
typical periods of idling, going uphill, going downhill, traveling slowly with frequent stops,
driving in quiet residential neighborhoods, and moving quickly along boulevards. Altogether,
we collected nearly 20 hours of sampling results on four school buses. 25 In order to determine
other factors that may affect a child’s exposures inside the bus, we compared the air in the
front and the back of the interior of the bus and compared the air quality with the windows
open and closed. The monitoring instruments were checked to assure comparability by
running the instruments side-by-side before and after the testing.
6
Because the bus was virtually empty rather than loaded with children, the engine may have
been under less strain and the diesel emissions may have been lower than on buses loaded