The power to decarbonise rail.

James Holmes, Business Director
Ian Fowler, Business Director
08 January 2024
Multiple trains parked as a depot
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Electrification is the key to decarbonising the UK rail network. But it is an expensive and very technically challenging task that requires new thinking to embrace systematic, locally focused solutions, if the UK rail sector is to meet its carbon reduction goals.

In March 2021, Members of Parliament on the House of Commons Transport Select Committee described rail electrification as “the only immediately viable decarbonisation option for most of the network” and a critical part of the UK’s overarching journey towards a net zero future.

Certainly, the committee highlighted the value of investing other carbon reducing technologies such as hydrogen and fully battery powered rolling stock, but the conclusions from its report “Trains Fit for the Future” were clear: we urgently need to press forward with electrifying the network, and if the UK is to meet its 2050 decarbonisation targets, investment in rail electrification had to start immediately. 

Fast forward to today and the UK’s electrification programme is working hard to meet the targets set in Network Rail's Traction Decarbonisation Network Strategy which identified a goal of electrifying some 13,200 track km of line by 2050 – around 450 track km a year.

In reality, the Office of Rail and Road Regulation estimates that in 2020-21 the figure achieved was just 179 track km and in 2021-22 it was just 2.2 track km.

Understanding the cost of electrification

The reasons behind these delivery figures are clear; electrifying the whole of the UK rail network is a very technically complex task and one that, using current technologies and techniques, is proving prohibitively expensive. Network Rail estimates the cost to be between £18bn and £26bn, largely due to the complexity and time taken to plan and install new overhead power lines on existing routes. 

At Amey we are addressing these challenges head-on while working with Transport for Wales (TfW) to upgrade and enhance the Wales & Borders rail network. A major part of this work is electrification of the Core Valley Lines (CVL) linking Cardiff to the towns of Aberdare, Merthyr Tydfil, Treherbert, Rhymney and Coryton as part of the new South Wales Metro which, in line with the Welsh Government’s Well-being of Future Generations Act, is designed to put the long-term wellbeing of people and communities at the heart of all public investment decisions. 

Our solution for CVL was to embrace the concept of ‘smart electrification’, a new way of approaching the challenge to maximise efficiency of the construction, and control costs, by avoiding the need to invest time and money needed for full overhead line electrification (OLE) installation along the complex CVL route.

Essentially, we've adopted a smart electrification process on the Core Valley Lines. We have designed the trains to suit the network rather than the network to suit the trains. That means we have not electrified every inch of the railway. We've been smarter about how we've done that.

The power retrofit challenge

While OLE power delivery remains the most efficient way to provide the large amounts of power required to drive heavy trains, retrofitting this technology to existing track layouts is both technically challenging and expensive. Many bridges are too low for safe installation of the high power 25kV power lines. The scale of engineering work required to rebuild bridges or lower the track raises the cost and increases the carbon footprint of any retrofit project.

The CVL route is a case in point. As the name suggests, the lines navigate difficult, undulating terrain, passing through tunnels, over and beneath existing roads and across rivers and valleys. The use of OLE, while desirable to deliver the large amount of power required to drive trains in this hilly geography, would have required a huge programme of bridge and tunnel reconstruction to create sufficient headroom for the OLE equipment. 

While the UK has a large number of track kilometres electrified using ground level DC powered third rail, the power requirements, rural locations and geography means that this technology is not a viable or safe solution for CVL. 

When it comes to operational efficiency, the higher the voltage the better because there is less current required for any set amount of power – which is why overhead is a safer and technically better solution.

Similarly, the use of pure hydrogen power was considered but ruled out due to efficiency and the weight and space required to carry enough fuel to run the service.

New hybrid technology solutions

A new breed of specially designed hybrid trains sit at the heart of our new delivery and operational strategy. The rolling stock was commissioned and built specifically for this contract: the Stadler Class 756 FLIRT, a tri-mode train capable of running on battery and diesel power in addition to OLE; and the Stadler Class 398 Citylink, a bi-mode metro-style train, powered by OLE and battery. 

Unlike most rail vehicles, these are specially designed to fit the service requirement and geography of the network, using a combination of external and on-board battery power to navigate the network. A sophisticated power management system maximises the distribution of power between OLE and battery power taking into account the geography, the dwell times, the number of stations, tunnels and bridges.

Without the use of this innovative solution the upgrade would have been hugely expensive in terms of cost and carbon and required the local road networks to be interrupted during the extensive work. 

It would also have meant the demise of many historic and locally significant structures on the South Wales rail network, many of which are listed. Any proposed modifications to these structures are usually very difficult and creates huge resistance to change from local communities. The use of hybrid trains accelerates delivery and reduces the risk of long periods of difficult and potentially divisive local community consultation.

One size does not fit all

Clearly, the use of hybrid rolling stock, relying on battery power to bridge the gap to permanently electrify sections of route, is well suited to this South Wales geography and service type with relatively low running speeds compared to the high speeds and large carriage numbers typical on the mainline. This means that the power demand can be more easily managed, allowing batteries to be quickly recharged when the train emerges back onto the OLE power. 

However, the disadvantage of these hybrid trains is that they are more expensive to purchase and more complex to maintain. And they also must be carefully matched to the terrain and services requirement, and managed while in operation to ensure that there is always sufficient power available to drive the train.
This requires complex technology to calculate and map the power demand at every point in the journey to ensure that the batteries are sufficiently recharged. This is not only to power the train through the planned current free sections of the route but also have sufficient in reserve capacity to cope with unplanned stops on route and to accommodate extra demand caused by specific track or passenger loading conditions. 

The design relies on the performance of the battery and the load placed on it, which means having a clear understanding of the geography – the gradients, dwell times and stations. The rolling stock therefore must fit the geography of the system and our design team has carried out a huge amount of battery modelling to make sure that the rolling stock can work with the discontinuous electrification in the geography on the CVL region. 

That said, battery technology is advancing rapidly, both knowledge of their performance and reliability of their acceleration. Once again, extensive battery modelling has been completed to make sure that the system is reliable and resilient, including development of a new software tool, that enables the CVL’s complex and varying conditions to be calculated as the trains move around the network.  

Establish teams; maintain the skills

When it comes to electrifying the wider UK rail network, one size does not fit all. If the economic and carbon cost of electrification is to be controlled, a consistent, locally focused programme approach backed by an integrated and experienced supply chain is vital. 

However, the reality is that this long-term programme does not yet exist, making it difficult for these skilled teams to be kept together, for learning to be shared and for technology to be developed. While single projects such as CVL allow ideas to the trialled and delivered, without longer term commitment to programmes the sector will struggle to leverage the lessons learned and end up delivering piecemeal, expensive, carbon intensive and locally disruptive solutions.
That means being able to plan work ahead to have the designs ready to go as funding becomes available and crucially having the teams in place ready to carry out the work. 

Already the Amey electrification delivery team is being demobilised from the Cardiff area, split up and sent to work on projects elsewhere in the UK despite the certain knowledge that in the not-too-distant future there will be a need for similar electrification in the Swansea area. Bringing these skills and relationships back together will clearly only add to cost, time and complexity going forward.

The need for a programme approach to electrification 

Having pushed at the boundaries of what can be achieved in terms of accelerating the delivery of rail electrification, the challenge for the CVL electrification team is to work with the supply chain to continue this technology roll out and development across the wider network. 

As highlighted by the Transport Select Committee report: “Electrification should be delivered through a long-term rolling programme, in which the Department, Network Rail and the wider industry learn the lessons of earlier schemes and strive to reduce the costs.”

Such a programme approach is key to simplifying and controlling the cost of procurement across the supply chain, allowing teams and decisions to be better integrated across the entire value chain - increasingly vital given the impact of inflation on material prices in the sector. 

The key is integrated decision making, so everybody in the value chain is involved. To make a good quality set of decisions around electrification, you've got to have vertical integration. Everybody needs to be involved.

It requires a system thinking approach, where we, as an industry, come together and work towards holistic, shared outcomes for what we want from infrastructure, and empower local teams to do what is right for their geography, terrain and communities. 

Fundamentally, establishing that long-term rolling programme - and the funding that sits behind it - is crucial to decarbonising the sector and helping the UK meet its net zero carbon challenge. Surety of workload means that across the supply chain, we can invest in innovative ideas, press forward with designs and establish the skilled teams needed to deliver change. 

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