Professor Paul Allen discusses decarbonising the UK’s railways

With the UK Government seeking a national net carbon zero target by 2050, Rail Minister Jo Johnson challenged the rail industry to remove all diesel-only trains from the network by 2040. This set in motion a shift in rail sector focus to the development of solutions for decarbonising UK railways.

It is accepted that to achieve this ambitious target, the Government must play its part in developing a viable, workable strategy, and levy funds to support a mix of substantive extension of cost effective continuous rail electrification, combined with appropriate deployment of emerging zero-carbon traction solutions such as hydrogen and battery power. At this juncture, it is worthy of note, that due to a low rolling resistance, rail vehicles inherently offer far lower specific energy consumption per t/km than their road vehicle counterparts, and hence beyond a focus on rail decarbonisation, the Government should also seek to incentivise modal shift from road to rail – success on this front has the ability to return far greater carbon savings than rail decarbonisation alone1.

Once again considering the topic of rail decarbonisation, key industry stakeholders including Network Rail, passenger and freight train operators and leasing companies, will be required to set out plans to deliver against future targets laid out by Government; not a trivial task when considering residual life and value of existing fleets, the costs of re-engineering, and the required investment in infrastructure for enabling works such as rapid battery charging and the supply and delivery of hydrogen across large parts of the network.

The latest hydrogen powered train concepts are currently being targeted for services that would replace typical diesel multiple unit routes, with speeds less than 100mph and a maximum range of up to 600 miles. In such a configuration, a three car unit would essentially become a 2.5 car unit to accommodate hydrogen storage. The technology would sensibly be targeted at self-powered operation on suburban lines that are not prioritised for continuous electrification. Hydrogen trains with higher speed and range capabilities may be developed in the future, but the business case for the required larger hydrogen tenders is likely to prove a significant obstacle. Hydrogen and battery solutions can also be incorporated within hybrid vehicle concepts, thus helping to facilitate reduced cost, discrete electrification programmes, by allowing for relatively short hops ‘off the wire’ prior to re-joining an electrified route. In this mode of operation, current range limitations of battery technology can be mitigated as batteries are recharged whilst running under the wire.

With such range limitations, opportunities for adopting battery-only, self-powered trains seem to be limited to non-electrified routes that offer short hop journeys, with operational headway for rapid charging at each end of the line. This mode of service is demonstrated by concepts such as the Class 230 battery vehicle running on rural lines between Bedford and Oxford. As battery technology improves in terms of speed and range limitations, then battery-only concepts may be able to compete with hydrogen fuelled counterparts.

Freight and higher speed passenger services (greater than 100mph) that demand high traction power levels create a greater decarbonisation challenge; energy density and constraints on space imposed by a restrictive UK loading gauge, limit the application of fuelling and hybridisation options. Space constraints therefore place a focus on technology developments that can reduce the size of hybridisation hardware. For example, silicon carbide components in power electronics significantly increase electrical efficiency, reducing inverter drive sizes, thereby offering crucial benefits for packaging hybrid traction equipment in higher power applications.

Such incremental developments that can reduce carbon emissions for existing diesel-based technology may need to be adopted to form a ‘stop-gap’ whilst new electrification programmes and technologies with higher energy and power densities emerge.

The wider roll-out of green-grid rail electrification remains the most sensible and pragmatic option to decarbonise UK railways. When considering future electrification strategies, the UK’s Railway Industry Association (RIA) found that depending on the complexity of the geotechnical and engineering requirements, electrification could be achieved for between £0.75m and £1.5m per single track kilometre2. Realising such figures requires a strategic approach to electrification; a review of ‘lessons learnt’ and development of a long-term rolling investment programmes that encourage innovation and competitive pricing from suppliers, and retention of knowledge of how to electrify efficiently and cost effectively.

From a strategic research and development perspective, informed by the UK industry’s Decarbonisation Taskforce Report3, five key targets have been identified for inclusion in a five year research plan to help realise the 2050 net carbon zero ambition, and are to be included within a planned update to the national Rail Technical Strategy (RTS):

  • Freight and yellow plant decarbonisation, building on the current RSSB-led research project
  • Increasing the capabilities of battery and hydrogen, including through developing appropriate infrastructure and reducing whole system costs
  • Reducing the whole system cost of electrification, including through various forms of intermittent electrification
  • Increasing efficiency of both current and future rolling stock as well as infrastructure
  • Increasing the ability to model and measure system wide carbon emissions, arising from both operational and capital works

Finally, as an example of how technology transfer from other sectors can offer potential interim solutions for the most challenging of decarbonisation problems, funded by RSSB’s decarbonisation research initiative, the University of Huddersfield’s Institute of Railway Research is working with Artemis Intelligent Power and freight operator DRS, to reduce freight locomotive and yellow plant carbon emissions.

The research project will examine the benefits offered by mechatronically controlled digital displacement pump technology as a more efficient alternative to conventional hydraulic pumps. Use of this technology, which was originally developed for the wind power and road plant sectors, has been proven to yield fuel savings of up to 20 per cent in providing traction and auxiliary power for rail applications.

Professor Paul Allen is Assistant Director of the Institute of Railway Research (IRR) at the University of Huddersfield. The IRR is an internationally leading research group that has been established for over 20 years and brings together some of the most highly skilled railway researchers in the UK. The IRR employs a team of 35 multi-disciplinary staff with capabilities including vehicle and track system dynamics, traction, braking and energy systems, pantograph and overhead line dynamics, advanced safety management, data analytics, asset condition monitoring and railway technology development.

[1] Dept. for Transport, ‘Rail Freight Growth Market Review & Modal Shift Model Outline’, DfT-RFG&MS01, September 2016
[2] Rail Industry Decarbonisation Task Force, ‘Final Report to the Minister for Rail’, July 2019
[3] Railway Industry Association (RIA), ‘RIA Electrification Cost Challenge’, March 2019