Background

Diesel engines are almost universally used in heavy-duty trucks, ships, locomotives, construction equipment, and buses, and the design remains largely unchanged since the technology’s invention in 1893.

While diesel technology has been commercially available since 1895, the use of diesel engines in school buses only started during the gasoline shortages and price spikes of the mid-1970s. When the decision to switch to diesel was made, the adverse health effects of diesel emissions were not known.

However, we now know that diesel exhaust contains dozens of chemicals considered by the U.S. Environmental Protection Agency (EPA) to be hazardous air pollutants. Diesel exhaust is classified as a probable human carcinogen by a number of governmental authorities including the International Agency for Research on Cancer (IARC), the U.S. National Toxicology Program, and the U.S. Environmental Protection Agency, and is labeled as a known carcinogen by the State of California.(1)

Despite a growing body of evidence regarding the health hazards of diesel, school buses in most states are exempt from routine emissions testing. As a result, children have been exposed to increasing levels of toxic chemicals and fine particulates on a daily basis as the number of diesel trucks and buses on our roads continues to rise.

Today, well over half of the nation’s 600,000 school buses run on diesel fuel – buses that are responsible for bringing 24 million children to school each day.(1)

While the EPA has instituted tougher diesel standards, these stricter regulations are not due to be phased in until 2006-2010. Even if these regulations are phased in on time and enforced properly, they may not be stringent enough to fully protect our children’s health.

Diesel emissions have been linked to the aggravation of asthma, bronchitis, pneumonia, retarded lung development, and increased emergency room visits for respiratory illnesses.

Children who ride a diesel school bus may be exposed to up to four times more toxic diesel exhaust than someone traveling in a car directly in front of it. The excess exhaust levels on the buses are more than eight times the average levels found in the ambient air in California and 23 to 46 times higher than levels considered to be a significant cancer risk according to the EPA and federal guidelines.(2)

Studies in California and Connecticut have found levels of diesel exhaust inside school buses are often higher under certain circumstances – when buses idle with windows open, run through their routes with windows closed, engage in stop-and-go or hilly driving and, especially, when they are queued to load or unload students while idling.(1)(2)

State governments must act aggressively to replace diesel engines with cleaner alternatives if we are to successfully reduce smog and particulate pollution and minimize the serious cancer threats posed by diesel exhaust.(2)

Environmental groups have been publicizing the dangerous effects of diesel for years, but have been largely unsuccessful at prompting action until recently, due largely to diesel engine durability and longevity and resistance from trucking industries. The Natural Resources Defense Council published a series of studies on dirty diesel during the 1990s to little avail, but legislative action was spurred on by their 2001 report, “No Breathing in the Aisles,” which documented the poor air quality inside school buses and the effect it could have on children’s health.(2)

A number of states have since passed legislation to reduce the harmful effects of diesel emissions on schoolchildren. State approaches in tackling this serious problem vary from anti-idling regulations to programs designed to help provide funding to retrofit or replace old diesel buses. To see a list of enacted and pending state legislation on this issue, please see the School Bus Emissions State Info page.