Ian Johnson, Head of Profession for WSP’s UK Rail discipline, describes the transformational change required to deliver decarbonisation on the UK’s rail network…

The decarbonisation of the UK’s transport infrastructure has come into sharp focus over the last year following legislation signed by the UK Government in June 2019 to bring all greenhouse-gas emissions to net zero by 2050.

Rail has an essential role to play in the UK’s transition to a net zero economy. The work undertaken by the rail industry task force in response to a challenge from the former Rail Minister, Jo Johnson MP, to remove all diesel-only trains from the UK network by 2040 concluded that decarbonisation is possible, supporting the landmark legislation.

However, it will require significant coordinated investment in both infrastructure and rolling stock, with a degree of urgency, given the scale of infrastructure works likely to be required and the timescales for fleet replacement or upgrade.

Where are we today?

The Department for Transport has recently published a policy paper explaining how it intends to develop a plan to meet the target of net zero transport emissions by 2050. The plan is scheduled to be published later this year.

In the meantime, Network Rail is due to publish its Traction Decarbonisation Network Strategy (TDNS) in the coming months which builds on the decarbonisation task force output last year. This will inform decisions around which traction solutions could work on which routes for both passenger and freight; it will be a crucial roadmap to inform the industry plan.

A rolling programme of electrification is likely to be required, whilst utilising new technologies such as battery and hydrogen propulsion on other routes, provided that the energy supply can be made zero carbon.

What are the viable solutions?

It is clear that overhead electrification is the only viable option for high speed and long-distance routes, as well as for freight. It is, however, a costly solution, particularly when accounting for the impact on overline structures and other rail systems and is not therefore suitable for deployment on all routes.

Aside from electrification, battery and hydrogen propulsion are the only two viable alternatives. Maintaining the existing loading gauge means that, without sacrificing carrying capacity (passengers or freight goods), both have limitations in terms of achievable performance and range.

While technology is evolving, batteries are currently best suited to support ‘discontinuous’ or end-of-line electrification, low speed, short stop, applications including light rail. Trials of battery-retrofitted EMUs have been successfully undertaken and we have seen the application of battery technology in the CAF Urbos trams that will run “catenary-free” in the new Centenary Square extension to Midland Metro. Battery propulsion is also proposed for the innovative Very Light Rail (VLR) system currently being developed by Coventry City Council.

Hydrogen trains represent a potentially viable option for rural lines, with trials of re-purposed EMUs currently ongoing in the UK. The German public transport network Rhein-Main-Verkehrsverbund (RMV) subsidiary, Fahma, has placed an order for 27 Alstom Coradia iLint hydrogen model trains to replace existing diesel trains. Interestingly, the contract also includes the supply of hydrogen, maintenance and provision of reserve capacities for the next 25 years.  Notwithstanding the success of the ongoing UK trials and the findings of TDNS, the viability of hydrogen as a solution will depend on the ability to generate, distribute and store ‘green’ hydrogen in a cost-effective way.

One key challenge we face in decarbonising rail in the UK is freight. Despite 42 per cent of the UK rail network being electrified, only 13 per cent of freight trains are electrically hauled today. Given the power requirements for economic operation, electrification is the only viable solution. However, it is worth noting that the Committee for Climate Change (CCC) report, which underpins the net zero legislation, implicitly accepts some residual carbon emissions for rail freight where electrification is not practicable.

How do we reduce the cost of electrification?

Notwithstanding the clear benefits of electrification, the RIA Electrification Cost Challenge Report published last year made it clear that there was little Government support for further electrification without clear evidence of its affordability and deliverability against established industry benchmarks in the UK and overseas.

The Scottish Government is committed to electrification and has funded a rolling programme of seven schemes over the past ten years totalling 500 single track kilometre (stk). These have delivered electrification broadly within the target range of £1 million to £1.5 million per stk and the commitment to a rolling programme has enabled lessons to be learned and passed from one project to the next.

WSP is currently working with Network Rail and stakeholders to apply the emerging principles of ‘efficient electrification’ to the next tranche of schemes with the aim of further reducing unit costs. This includes contributing to these principles through various industry engagement activities.

  The key area of ‘efficient electrification’ that WSP is currently developing with Network Rail is in relation to the consideration of reduced electrical clearances. For any electrification project, a key consideration is the spatial requirement at overline structures to accommodate the 25kV overhead line equipment. The electrical clearances required from the train pantograph and overhead line equipment to overline structures and from the overhead line equipment to rolling stock dictate the spatial requirements at the structure. Using traditional electrical clearance values has led to significant costs for electrification route clearance, in the form of bridge reconstruction and/or track lowering, on most legacy electrification projects.

The ‘efficient electrification’ electrical clearance values that are being promoted by Network Rail and WSP at the development stage of key electrification projects in Scotland are far lower than the traditional values. These reduced clearance values have been justified by incorporating cost effective mitigation equipment, supported by trials and testing, and result in significant reduction of bridge intervention works. These initiatives will in turn lead to significantly reduced route clearance costs and help the case for making electrification more affordable.

What are the next steps?

Both UK Government and industry are committed to reducing the impact of rail travel on the environment whilst still offering an attractive service for customers.

While strategies and plans on how decarbonisation will be achieved are eagerly awaited, there is likely to be a strong case for electrifying a significant proportion of the network, including inter-city, commuter and freight routes that are not currently electrified. A commitment to developing a UK-wide rolling programme before current projects are completed is vital to ensure that the expertise, skills and capability are retained and developed to match the likely future demand.  A realistic programme, avoiding the peaks and troughs we have seen in the past, will ensure that incremental benefits are achieved and will boost confidence in the ability of the rail supply chain to deliver. It will also enable alignment with short, medium and long-term rolling stock fleet strategies.

From our experience of implementing ‘Future Ready’ zero emission solutions in other geographies, it is important that the feasibility, specification, procurement and delivery are considered from a whole system approach that includes energy supply as well as infrastructure and rolling stock.

Ian Johnson is Head of Profession for WSP’s UK Rail discipline