Electric vs. hydrogen fuel cell buses: A simulation-based well-to-wheel emission evaluation under dynamic operating conditions

As a key strategy for achieving CO2 reduction targets, zero-emission public transport has led many countries to adopt hydrogen fuel cell buses (HFCBs) and electric buses (EBs). Although EBs currently offer economic advantages, their comparative emission performance remains unclear. Here lies an important question: how do the emission performances of HFCBs and EBs compare under varying operating conditions, particularly within evolving energy systems characterized by different grid emission factors and hydrogen mixes? To answer this question, this study develops a VISSIM-based well-to-wheel simulation model to compare the emission performance of EBs and HFCBs using a Singapore road network. Multiple operating scenarios are generated by varying key parameters (e.g. speed limits, passenger load, and terrain), resulting in 2400 emission data points across four bus services. To reflect evolving energy systems, the analysis also incorporates different grid emission factors and hydrogen pathway mixes. The results show that (a) higher grid emission factors can make HFCBs achieve greater carbon reductions than EBs even with the current high share of grey hydrogen, whereas under lower grid emission factors HFCBs gain an advantage only when the grey-hydrogen share is substantially reduced; (b) HFCBs deliver more benefits at lower speeds and lighter passenger loads, making them particularly suitable for such routes during the early adoption phase when grey hydrogen dominates; and (c) terrain has a limited influence on WTW emission compared with speed and load. These findings provide operators and policymakers with guidance for planning zero-emission bus deployment tailored to local contexts and technological progress.