This note is intended to inform decisions and ensure the rail industry is aware of the challenges and limitations of these fuels.

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  • There is no long-term role for biofuels or synthetic fuels on a net zero carbon railway.
  • There is a defined pathway across the transport sector regarding demand management of available sustainable fuels.
  • The Traction Decarbonisation Network Strategy (TDNS) has proposed a pathway towards a zero-carbon traction scenario using electrification, hydrogen, and battery trains.

The Transport Decarbonisation Plan (TDP) commits that “We will deliver a net zero rail network by 2050, with sustained carbon reductions in rail along the way”. On the traction side, the TDNS Interim Business Case sets out how this will be delivered through a combination of electrification, hydrogen, and battery traction. 

Through the TDP, the Department for Transport has set out clear expectations for the changes in demand over time:

  1. In the short term, low carbon fuels will continue to be an available and flexible resource to deliver immediate emissions savings in all road vehicles. 
  2. In the medium-term, the need is expected to shift to long-haul heavy goods vehicles in the road sector.
  3. In the longer term, TDP notes there is expected to be increasing demand also from aviation and maritime which are likely to need the largest proportion of low carbon liquid or gaseous fuel. 

The TDP notes, “The availability of sustainable raw materials for low carbon fuels is however limited”, with other transport modes, such as aviation, which has no obvious alternative pathways to full decarbonisation, unlike rail, prioritised for any that may be available. The Department for Transport (DfT) nevertheless recognises “the potential value of sustainably sourced biofuels as a transitional technology, where their use is technically feasible and makes commercial and environmental sense” for rail. Some rail operators are exploring the use of biofuels and sustainable alternative fuels to achieve immediate carbon savings.   

This thinking was built into the work of the Rail Industry Decarbonisation Taskforce and the TDNS which both recognised that there was no realistic long-term prospect of biofuels availability at scale. Regular consultations with DfT since the publication of the Taskforce reports to the Minister for Rail in 2019 confirm that the position has not changed. 

It should also be noted that where low carbon fuels are derived from fossil fuels or from other sources where carbon emissions are a by-product of the manufacturing process, there will be a need for carbon capture and storage for such fuels to be genuinely net zero emissions.

At present, the air quality impact of most non-diesel fuels is unproven and there is limited evidence of any significant benefits. Air quality benefits when used in internal combustion engines therefore need to be more extensively studied. RSSB is developing an emissions testing protocol in project ‘T1235 - Performance requirements and testing protocols for emissions mitigation’. This will allow the air quality impacts of a range of fuels and emissions reduction technologies to be tested consistently with real world duty cycles.