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Selecting Buses with the Most Up-to-Date Environmental Controls and Safety Measures
Making the Way for Environmentally Cleaner Buses
In order for today's students to have the healthiest ride to and from school, consider purchasing school buses that meet future emission and safety standards. Bus engine manufacturers must meet current EPA emission standards for their new engines.
These standards target specific pollutants that are coming from the exhaust. However, future emission standards are even more aggressive than current standards, and school districts should work with their distributor to get the cleanest engine possible for their new buses.
The emission standards are to be met by those companies manufacturing the school bus engines so school districts are not required to do anything to comply with these standards. Bus manufacturers may be able to provide school districts with new buses that have additional technologies or controls to meet future emission standards, thus, providing the cleanest bus available.
The emission standards for diesel school bus engines were lowered in 2004 to reduce the oxides of nitrogen (NOx). However, further reductions of NOx and particulate matter (PM) will occur in order to address the health concerns associated with these pollutants. EPA established new emission standards for heavy duty highway engines which will begin to take effect in model year 2007. These are known as EPA's 2007 Model Year Heavy Duty Engine Standards (PDF, 4 pages, 120K, About PDF) (EPA 420-F-00-057, December 2000).
Table 1 compares the various heavy duty diesel engine emission standards set by EPA by the years that the engines were manufactured. Simply put, the newer buses have much lower emissions of pollutants than those produced before 1990, especially for PM and NOx. By replacing the oldest buses in the fleet with the lower emitting new buses, school districts can provide their students with a much cleaner bus.
US EPA Heavy Duty Diesel Engine Emission Standards:
| Engine Model Year | HC | CO | NOx | HC+NOx | PM |
|---|---|---|---|---|---|
| 1974-78 a | --- | 40 | --- | 16 | --- |
| 1979-83 b | 1.5 | 25 | --- | 10 | --- |
| 1984-87 | 1.3 | 15.5 | 10.7 | --- | --- |
| 1988-89 | 1.3 | 15.5 | 10.7 | --- | 0.6 |
| 1990 | 1.3 | 15.5 | 6 | --- | 0.6 |
| 1991-93 | 1.3 | 15.5 | 5 | --- | 0.25 |
| 1994-97 | 1.3 | 15.5 | 5 | --- | 0.1 |
| 1998-2003 | 1.3 | 15.5 | 4 | --- | 0.1 |
| 2004-06c, d | 0.5 | 15.5 | 2 | 2.4/2.5c, d | 0.1 |
| 2007 + e | 0.14 | 15.5 | 0.20 | --- | 0.01 |
Abbreviations: HC-Hydrocarbons CO-Carbon Monoxide NOx-Oxides of Nitrogen
HC + NOx-Hydrocarbons and Oxides of Nitrogen, combined standard PM-Particulate MatterNotes:
(a): Combined HC+NOx standard of 16 g/bhp-hr
(b) Combined HC+NOx g/bhp-hr
(c) Under a consent decree with EPA, many engine manufacturers implemented the 2004 standards in October 2002
(d) Emission Standard allows for the options of 2.4 g/bhp-hr non-methane hydrocarbons (NMHC)+NOx, or 2.5 g/bhp-hr NMHC+ NOx and 0.5 NMHC
(e) Emission standards phased in between 2007 and 2010 for NOx and Nonmethane Hydrocarbons. Phase-in compliance is based on a percent-of-sales: 50% compliance between 2007 and 2009 and 100% compliance in 2010. No phase-in schedule applies to particulate matter emission standards which must be met starting with the 2007 engine model year.
Bidding Process for New Buses
Bidding specifications for new bus purchases should include requesting
that engine manufacturers which are bidding provide information
about the emission levels of the new bus engines that have been
certified and specify if any additional technologies are available
to further reduce those levels. This could include EPA or the California
Air Resources Board (CARB) 
verified particulate filters or catalysts. Additional bus
safety considerations should be requested as a part of the specification process. Other
factors, such as overall emission reductions and safety improvements,
dealer proximity to school district, prior successful relationship
with dealer/manufacturer, etc., in addition to overall cost, may
need to be considered in comparing the bids.
Besides what has been listed in the School Transportation News,
information on school bus safety issues can be found at U.S. Department
of Transportation's School Bus Safety Program’s website.