近年來的人類活動，加劇了全球溫室效應及其引發之氣候變遷與災難以及食物和水源的短缺，人類活動當中又以運輸活動為溫室氣體排放主要來源之一。世界各地領袖及國際組織針對溫室效應及氣候變遷，紛紛提出減碳目標及策略，台灣交通部運輸研究所針對市區公車之減碳目標訂定為:「市區公車全面汰換舊型公車為替代能源公車」。因此本研究探討台南市客運量最大的市區公車路線2號公車之實際生命週期碳足跡，及若使用其他替代能源公車行駛時，其生命週期碳足跡及環境效益。以生命週期的觀點來分析不同能源公車在原料製造階段、運輸服務階段及廢棄物處理階段等各環節對於環境面之影響。
本文碳足跡評估方法依照國際標準ISO/TS 14067 為主要碳足跡評估架構，且參照另一國際標準PAS2050中的五大計算步驟做為評估碳足跡之流程，並服從CFP-PCR規範。本文以實際案例─台南市2號市區公車車輛為標的進行碳足跡評估，除收集一整年的直接活動數據及其他所需二手數據，以建立碳排放與碳足跡模型並繪製製程地圖外，並進行碳足跡數據品質分析。
公車碳足跡計算結果，以延人公里為單位，由大至小排序分別為：液化天然氣公車63.14 gCO2e/pkm、傳統柴油公車54.6 gCO2e/pkm、液化石油氣公車47.4 gCO2e/pkm、充電式純電動公車37.82 gCO2e/pkm及氫燃料電池公車29.17 gCO2e/pkm。分析各能源公車於各生命週期階段之碳排放熱點，發現傳統柴油公車、液化天然氣公車及液化石油氣公車，於運輸階段為主要碳排放生命週期階段，氫燃料電池公車及充電式純電動公車，則以燃料製造階段為主要碳排放生命週期階段。
研究發現利用氫燃料電池公車取代傳統柴油公車，為最具環境效益之方法，若在2025年汰換全部台南市2號市區公車共32輛公車為氫燃料電池公車，預計每年可減少1,244.08 tonCO2e；若在2025年汰換全台灣市區公車共15,663輛車為氫燃料電池公車，預計可減少227,832.39 tonCO2e。因此本研究建議，可使用最具環境效益之氫燃料電池公車，作為未來國家取代傳統柴油公車主要之替代能源公車。

One of the Taiwan's transportation policies to reduce CO2 emission is to replace all traditional diesel fuel urban buses with alternative energy buses. This paper uses a case study of bus route NO.2 in Tainan city and follow the international standard ISO/TS 14067 and PAS2050 to measure different energy buses carbon footprints . The purpose is to measure the environmental benefits of the alternative energy buses. The results of the calculation of the bus’ carbon footprints from large to less are LNG buses 63.14 g CO2e / pkm, traditional diesel buses 54.6 g CO2e / pkm, liquefied petroleum gas buses 47.4 g CO2e / pkm, Plug-in electric buses 37.82 g CO2e / pkm and hydrogen fuel cell bus 29.17 g CO2e / pkm, respectively. This paper found that using hydrogen fuel cell buses to replace traditional diesel buses have the most environmental benefits.Therefore, this study suggested that the government can use the most environmentally friendly hydrogen fuel cell bus as the future of the country's major alternative energy bus.

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