29 September 1998

The California Air Resources Board (ARB) adopted a resolution calling for a replacement of diesel-powered school bus fleet, as well as diesel transit buses, with natural gas powered units. The replacement should start with the oldest, pre-1977 school buses. The ARB will support all efforts to replace diesel-fueled school and public transit buses with alternative-fuel buses, including the provision of necessary infrastructure and technical training. The California air pollution control districts and air quality management districts have been urged to take a leadership role in implementing diesel school and public transit bus replacement.

Federal funds are available for the program through the US Transportation Equity Act for the 21st Century (TEA-21). The following targets for the natural gas bus purchases were recommended:

  • For school buses, replacement of the remaining 2200 pre-1977 Type 1 diesel buses by 2003, at an approximate annual cost of $60 million in TEA-21 funds and $8 million in local/state matching funds. This will be an important step toward the eventual replacement of all diesel-fueled school buses.
  • For public transit buses, replacement of the remaining 5000 diesel-fueled buses by 2010, and exclusive purchase of alternative fuel buses for fleet expansion, at an approximate annual cost of $180 million in TEA-21 and subsequent federal funds and $40 million in local/state matching funds.

This action follows the recent identification of diesel particulate emissions as a Toxic Air Contaminant. The ARB has initiated a risk management process for particulate emissions from diesel-fueled engines, including convening a Diesel Exhaust Advisory Committee to assist the ARB staff in the identification of measures and strategies to reduce these emissions and exposure to them.

According to ARB, older pre-1977 school buses emit three times more NOx than new alternative fuel school buses and four times more particulate matter (PM10). Therefore, "replacing diesel powered school and transit buses with cleaner, alternative fueled buses is a clean air strategy for meeting health-based air quality standards for ozone and particulate matter and has the added benefit of reducing exposure to diesel particulate emission."

ARB estimates that compressed natural gas (CNG) transit and school buses achieve a cost-effectiveness in the range of $10,000 and $12,000 per ton of emissions of NOx reduced.

Source: California ARB, Resolution 98-49