ivIn 2005, there were approximately 50,000 diesel powered public transit buses operating in the United States, consuming over 500 million gallons of fuel annually. The Clean Air Act identifies diesel powered motor vehicles, including transit buses, as significant sources of several criteria pollutants which contribute to ground level ozone formation or smog. The effects of air pollution in urban areas are often more significant due to congestion and can lead to respiratory and cardiovascular health impacts. Life cycle assessment has been utilized in the literature to compare conventional gasoline powered passenger cars with various types of electric and hybrid powered alternatives; however, no similarly detailed studies exist for mass transit buses.LCA results from this study indicate that the use phase, consisting of diesel production/combustion for the conventional bus and electricity generation for the electric bus, dominates most impact categories; however, the effects of battery production are significant for global warming, carcinogenics, ozone depletion, and ecotoxicity. There is a clear connection between the mix of power generation technologies and the preference for the diesel or electric bus. With the existing U.S. average grid, there is a strong preference for the conventional diesel bus over the electric bus when considering global warming impacts alone. Policy makers must consider regional variations in the electricity grid prior to recommending the use of battery electric buses to reduce CO 2 emissions. This study found that the electric bus was preferable in only eight states including Washington and Oregon. Improvements in battery technology reduce the life cycle impacts from the electric bus, but the electricity grid makeup is the dominant variable.

Life Cycle Analysis of Natural Gas Extraction and Power Generation 3 Upstream Data Upstream data include the supply shares of natural gas and coal, as well as the energy requirements and material flows for the key activities for extraction, processing, and transport. These data are used to model the RMA and RMT stages in NETL's natural gas and coal models. 3.1 Natural Gas The primary unit processes of this model are based on data compiled by NETL. Secondary unit processes, such as production of construction materials besides steel, are based on third party data. Appendix A includes details on how these data are assembled in a model and references the detailed documentation in NETL's unit process library. Where data for the inventory are available, high and low values are collected, along with an expected value. When results are presented, three cases are shown: an expected case, a high case, and a low case. The high and low results (error bars on the results) are a deterministic representation of the variability on the data and not indicative of an underlying distribution or likelihood. 3.1.1 Sources of Natural Gas This inventory and analysis includes results for natural gas domestically extracted from seven sources in the lower 48 states:

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