Key Facts:
- In 2005, more than 60 percent of the 9.7 billion transit passenger trips in the United States were provided by buses, approximately 84 percent of which are powered by diesel combustion engines.
- Diesel exhaust contains ozone precursors, benzene, arsenic, dioxins, formaldehyde and other toxic substances and is a significant contributor to airborne concentrations of fine particulate matter (PM). Significant health impacts including lung damage and premature death are associated with exposure to fine particulate matter. It can also aggravate conditions such as asthma and bronchitis. Diesel exhaust has also been classified as a probable human carcinogen with no known safe level of exposure.
- In response to air quality and health concerns as well as rising fuel costs, a growing number of transit agencies are turning to hybrid-electric buses, which consume less energy and produce significantly fewer emissions by combining an internal combustion engine with an electric motor.
