Could urban electric public bus really reduce the GHG emissions: A case study in Macau?

Abstract

The urban bus fleet has been significantly expanded to satisfy an increasing demand for transit in Macau, highlighting the need for green transport. Electric public buses (EPBs) have been considered an effective strategy to reduce greenhouse gas (GHG) emissions by substituting them for diesel buses. However, the efficiency of EPBs to reduce GHG emissions varies significantly, due to local road conditions and transit operating characteristics. On the basis of the real-world tested data, this study performed a comparative life cycle assessment (LCA) between traditional diesel public buses (TDPBs) and EPBs to evaluate the actual GHG emissions and their reduction. The results show that the mean GHG emissions per 100 km of diesel light duty buses, medium duty buses and heavy duty buses were approximately 47.18, 101.97, and 127.99 kg CO2 eq, respectively. The EPBs supported by current electricity mixes exceed the emissions of corresponding TDPBs when considering the charging loss and electricity distribution loss. EPBs, therefore, would hardly reduce GHG emissions under the current situations. Due to the rapid growth in the number of urban buses, total GHG emissions from TDPBs in 2001–2015 experienced a rapid upward trend, increasing from 36.55 to 48.86 thousand tons CO2 eq. Scenario analysis for future EPBs substitution implies that, if choosing the best charging efficiency and electricity distribution loss, EPBs have the potential to significantly mitigate the GHG emissions from public buses, especially under the clean electricity mixes (like natural gases fired electricity and solar energy).