This research is an investigation of public transport carbon footprints using a life cycle assessment (the model of total carbon footprint as Eq. 1 on page 17) considering four different types of fuel (diesel, electric, liquefied natural gas, and hydrogen). This paper refers to ISO 14040:2006 and ISO 14067:2018 to evaluate the carbon footprints of these four different types of fuel. The bus transportation service in Kaohsiung, Taiwan, is the object, focusing on the route with the largest number of passengers. The results reveal that the hydrogen fuel cell bus emitted the least GHGs over its life cycle, with a reduction of − 67.52% compared to a diesel bus, while the electronic bus emitted − 55.13% less GHG over its life cycle, and the liquefied natural gas bus emitted − 45.81% less. These mean diesel buses and liquefied natural gas buses accounted for the most emissions in the bus service fuel phase of the carbon footprint life cycle. However, electric and hydrogen fuel cell buses do not emit GHGs in the bus service phase in terms of fuel. The phases involving the extraction and manufacturing of raw materials for both kinds of buses account for most of the life cycle emissions. In conclusion, the results of this study show that the hydrogen fuel cell bus has the greatest effects with regard to reducing GHG emissions among the three types of buses under consideration, and so, it is recommended that hydrogen fuel cell buses be widely applied in bus transportation in the future.
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