Life-cycle cost and emissions assessment of alternative fuel buses: a case study of the Delaware Authority for Regional Transit (DART)
Date
2010
Authors
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Publisher
University of Delaware
Abstract
The Energy Policy Act of 1992 motivated transit agencies to utilize alternative-fuel transit buses in addition to their popular diesel buses. The Delaware Authority for Regional Transit (DART) has also planned to add a significant number of alternative-fuel buses to its current transit fleet. This study has been defined to assist the DART administration to make an optimal decision in this regard. The information used in this study was gathered from the latest scientific and practical reports published by Federal Transit Administration (FTA), Transit Cooperative Research Program (TCRP), National Renewable Energy Laboratory (NREL), and the United States Environmental Protection Agency (EPA). It also combined with the knowledge that the author gained from two major recent conferences related to public transportation; 1) BusCon 2009 in Chicago, Illinois, and 2) APTA annual meeting 2009 in Orlando, FL. Among eight alternative-fuel buses introduced by the Energy Policy Act of 1992, this study recognized that only Compressed Natural Gas (CNG), biodiesel, and hybrid-diesel buses can be considered as the viable alternatives for the Ultra-Low Sulfur Diesel (ULSD) transit buses. For each of these technologies Life-Cycle Cost (LCC) and emissions are estimated and compared with the available information for the ULSD buses. The LCC consists of capital cost and operating cost. The capital cost includes initial purchasing cost and infrastructure cost which is separated in two subsections, refueling station and depot modification. The operating cost includes fuel cost, total maintenance cost, facility (refueling station and depot) maintenance cost, compression electricity cost (applicable to CNG buses only), and battery replacement cost (applicable to hybrid diesel-electric buses only). The results show that buses propelled by hybrid-diesel engine have the least LCC ($/mile). Alternatives were ranked with respect to their capital cost as follows: 1) ULSD, 2) Biodiesel, 3) Hybrid diesel-electric, and 4) CNG. The ranks of alternatives changed with respect to their operating cost and it was as follows: 1) CNG, 2) Hybrid diesel-electric, 3) ULSD, and 4) Biodiesel. Although all the alternative-fuel buses meet the latest EPA emissions standard, the recent scientific reports prove that hybrid diesel-electric buses emit fewer air pollutants than their counterparts. This characteristic also gives hybrid buses an edge to consider as the most suitable alternative-fuel buses for DART. This study found that CNG buses are the strongest competitor for the hybrid diesel-electric buses. The major problem with CNG buses for being utilized by DART is their cost of implementation. The infrastructure (refueling stations and depot modification) cost of CNG buses is very high. This issue gets worse because DART demands more than one infrastructure to be able to operate CNG buses throughout the state of Delaware. Also, DART needs to wait until the required infrastructures have been built meaning that the readiness index of CNG technology for DART is very low. This study also conducted an expert survey in order to determine the relative importance of other criteria on the transit fleet expansion plan. Four major goals and twelve criteria were defined. A questionnaire was designed and distributed among the relevant decision-making experts from governmental agencies, bus manufactures, academic organizations, energy suppliers, and research institutes. They assessed the relative importance (subjectively) for each of the criteria. The collected data shows that energy independence criterion is the most important factor in evaluating the alternative-fuel buses; second in importance are energy availability and safety; third is energy efficiency, indicating the need for new alternative-fuel buses. The survey also asked the respondents to rank the alternatives regarding each criterion. Based on the results, hybrid diesel-buses were ranked first in six criteria including energy availability, safety, energy efficiency, air pollution, noise pollution, and sense of comfort. Hybrid diesel-electric buses also were ranked second in two criteria including energy independence and cost of implementation. These buses were only ranked lowest with respect to the cost of maintenance criterion. However, this observation is not supported by our estimation and comparative analysis reports published by other organizations. The expert survey results clearly show that ULSD buses are the most reliable and capable alternative among other technologies. These buses were also ranked first with respect to the cost of implementation and cost of maintenance criteria. However, ULSD buses were ranked third and fourth (lowest) with respect to the most important criteria including energy independence, and energy efficiency. These buses were also assumed to perform poorly with respect to noise pollution, sense of comfort, and air pollution criteria. This study concludes that hybrid diesel-electric buses rate well according to the criteria of energy, environmental impact, industrial relationship, and implementation cost for DART. The results of this study also confirm that each transit agency needs to consider its unique characteristics and facilities before deciding what alternative-fuel bus to invest in. Two major reasons that support this conclusion are 1) Capital cost varies based upon facilities that transit agencies already have in place, and 2) Even for one transit agency, the best option may change based upon the number of buses that will be acquired. Life-cycle cost is sensitive to the number of buses that will be purchased. However, transit agencies can use other transit agencies experience or studies such as this thesis to perform their own study.