TECHNICAL PROBLEMS AND POLICY ISSUES ASSOCIATED WITH THE 1991 BUS EMISSIONS STANDARDS

An overview is presented of the problems that may be created for transit systems if the strict 1991 bus particulate and nitrogen oxides emissions standards remain in force. The problems created for manufacturers of diesel bus engines by the standards' tighter technology development schedule for buses than trucks are reviewed. Introducing the perspective that emissions from transit buses should be thought of in terms of emissions per passenger mile calls into question the need for the 1991 standards to be stricter for buses than trucks. The unique spatial relationships among buses, downtown pedestrians, and metropolitan places of residence are taken into account when evaluating the differing effects of bus emissions of nitrogen oxides and particulates. There appears to be far less justification for significant reductions of nitrogen oxides emissions from buses than for reductions of particulates. The more stringent the nitrogen oxides standards, the more costly and difficult it becomes to meet any given particulates standard. By analyzing the likely decisions of transit operators under the existing standards, an argument that slightly less strict standards would actually have the effect of causing lower total particulate emissions is developed. Accordingly it is argued that the Environmental Protection Agency should reconsider and slightly revise upward the 1991 standards. The 1994 standard, which is identical for buses and trucks, is not challenged.