It identifies a number of main pillars for reducing CO₂ emissions arising from energy consumption within the rail sector. Similarly, the production of hydrogen to power HMUs can also result in CO₂ emissions, which need to be taken into account. Fig 2 presents the estimated CO₂ emissions for HMUs, BEMUs, and HDMUs using biofuel, normalised to EMU operation. From a global carbon cycle perspective, this process can theoretically result in net-zero CO₂ emissions (Fig 5). Therefore, even the use of 100% biofuel does not currently achieve net-zero CO₂ emissions.