Diesel Particulate-Matter Filters: Ceramic devices that collect the soot in the exhaust stream and break it down into a cleaner substance. Must be used with ultra-low-sulfur diesel. Cost of a single filter kit can range from $5,000 to $10,000.
Diesel-Oxidation Catalysts: Devices that use a chemical process to break down pollutants in the exhaust stream into less harmful components. Can be used with regular diesel fuel. Cost ranges from $1,000 to $2,000 for a single catalyst.
Ultra-Low-Sulfur Diesel: This cleaner fuel will be available nationwide in June 2006; today it can be found only in certain parts of the country. Price differences between ultra-low-sulfur and cheaper, regular diesel fuel range between 8 cents and 25 cents per gallon.
Compressed Natural Gas: Domestically produced fuel that can reduce emissions of particulate matter by 70 percent to 90 percent. Costs of natural gas and diesel fuel are similar, but a new compressed-natural-gas bus costs $30,000 more than a new diesel school bus. In addition, buses that run on compressed natural gas require special fueling and maintenance facilities.
Anti-Idling Policies: Restricting idling can reduce harmful emissions in school zones and also save some money. Idling school buses typically use about a half-gallon of fuel each hour. If a fleet of 50 buses cut idling time for each vehicle by 30 minutes a day, the fleet could save $2,250 per school year in fuel costs.
SOURCE: U.S. Environmental Protection Agency
A version of this article appeared in the May 12, 2004 edition of Education Week as Routes to a Cleaner School Bus