Human activities have exacerbated the global greenhouse effect, resulting in extreme climate changes that have caused disasters and food and water shortages in recent years. Transportation is one of the main causes of global greenhouse gas (GHG) emission. Therefore, policy makers must develop feasible strategies to reduce GHG emission. One of Taiwan's policy is to replace traditional diesel fuel urban buses with alternative energy buses. This paper uses a case study of city bus route No. 2 in Tainan City following the international standard ISO/TS 14067:2013 to measure the carbon footprint of different energy buses. The bus carbon footprints measured from high to low as: LNG buses, 63.14 g CO2e/pkm; traditional diesel buses, 54.6 g CO2e/pkm; liquefied petroleum gas (LPG) buses, 47.4 g CO2e/pkm; plug-in electric buses, 37.82 g CO2e/pkm, and hydrogen fuel cell buses, 29.17 g CO2e/pkm. If all urban area public buses in Taiwan were switched to hydrogen fuel cell buses, this would reduce CO2e footprint by 227,832.39 t annually. This reduction is equivalent to planting 22.78 million trees. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.