Reimagining Transport: Hydrogen Trains


In the first in our Reimagining Transport series, we look at the potential for hydrogen powered trains to become a part of the rail network’s move to net-zero. Already in operation in select rail lines in Europe and with several other projects under development, hydrogen fuelled trains (alongside those which run on electrified lines) look to further prove their ability to replace diesel trains for some journeys over the coming years. This article suggests that there is reason for cautious optimism about the development of low-carbon hydrogen and, as a result, the decarbonisation of the rail network.

Using hydrogen in transport is not a concept of the climate change era; General Motors developed a prototype of a hydrogen powered van in 1966 (which was ultimately scrapped due to costs). However, while these developments are not entirely unprecedented, it is the advancement and the rate of advancement in hydrogen technology over recent years that have allowed hydrogen trains to come to the forefront of technologies being considered for decarbonising rail transport.

Recap on hydrogen as a fuel

Hydrogen is an attractive prospect as a fuel as the by-product at the point of consumption can solely be water, meaning no greenhouse gas emissions are produced and resulting in better air quality for the surrounding population. That does not necessarily make hydrogen a clean energy source – hydrogen is only as clean as the process used to produce it. Broadly, as further explained in the CMS Expert Guide to Hydrogen Projects, to be low-carbon the hydrogen should be either:

  • “Blue” hydrogen (i.e. where a carbon capture and storage system captures the carbon dioxide emitted as part of the steam methane reformation process to prevent its release to the atmosphere); or

  • “Green” hydrogen (i.e. one produced using electrolysis powered by electricity generated from a renewable source).

Hydrogen is very much a product in its development meaning that low-carbon hydrogen is not currently economically competitive – for example, currently only around 4% of the world’s hydrogen is “green”. If hydrogen is to be a viable clean energy source, the economics of the production of such hydrogen need to improve.

Another key issue with hydrogen is that it is not energy dense compared to diesel fuels that are currently used, and as a result it needs to be stored either in liquid form below -252.8°C (which is not currently feasible on a large scale) or stored at pressures of around 5,000 – 10,000 psi (for context, Earth’s average atmospheric pressure is around 14.7 psi). As a result, hydrogen fuel requires specific storage and transport infrastructure, and storage at this pressure means that the tanks need to be handled with care.

Hydrogen is often used in a fuel cell system. In a fuel cell, electricity is generated by an electrochemical reaction, and at the end of the process hydrogen combines with oxygen to produce water. Hydrogen can also be used in a combustion reaction – such as in a modified internal combustion engine of a car – however its combustion results in nitrogen oxide pollutants so is less attractive from an environmental perspective.

But there are other pros and cons of using hydrogen as the preferred train fuel – see table below for the key considerations.



Hydrogen technology is believed to result in less pollution (compared to using typical lithium-ion batteries which have a limited lifecycle and are hard to recycle) and reduces dependence on fossil fuels, while using a widely available resource – hydrogen.

Sceptics point towards the difficulties of turning hydrogen technology into large scale production, emphasizing the high costs associated with the manufacturing, operation and infrastructure of the technology (e.g. vehicles already available on the market cost almost twice as much as comparable fully electric or hybrid ones).

Similarly, there is currently a lack of available fuelling infrastructure.

Hydrogen powered trains allow for longer range transport, similar to hydrogen fuel cell cars.

One key drawback is that hydrogen’s lack of energy density means that it cannot currently meet the power needs of high-speed or freight services. This means that, on current technology (and the technology we need to act on to achieve net zero), electrification is the only option for high-speed and freight services.

It is widely accepted that outdoor accidental releases of hydrogen from single vehicles will disperse quickly, and not lead to any significant explosion hazard.

Safety could become an issue in particular cases, such as train stations, tunnels, or workshops.

Hydrogen technology is not novel, and trials and use in other industries (e.g., storage of hydrogen and operation of pipelines, the use of hydrogen as a process gas in the oil industry) have confirmed that it is a safe practice. Many experts have agreed that hydrogen fuel cell vehicles are even safer than cars with internal combustion engines.

It has been pointed out that hydrogen onboard a train may pose a safety hazard, due to possible tank failures (e.g. leaks or ruptures) and undesired chemical reactions.

However, research studies and input from the car industry address these concerns.

The risk of a leak and an explosion by a hydrogen tank is also nowadays lesser, since the tanks are often made out of Kevlar, a material resistant to bullets, thus further confirming the high safety of the tanks storing the fuel (which has also been tested through numerous crash tests).

Decarbonising the rail network – the options

A number of counties, such as the UK have ambitious net zero strategies which aim to encourage the use of trains over road transport. This is true for both passenger and freight services. Simply encouraging the transport of people or goods via the rail network in itself reduces greenhouse gas as rail more efficiently uses fossil fuels. However, given that many of the trains are powered by diesel and are not electrified, to achieve the decarbonization aims, options such as powering trains with hydrogen are amongst the options on the table. 

Why hydrogen and not electrification of all power lines? Well, electrification comes at a cost. For example, the UK Network Rail currently estimates track electrification at £1m - £2.5m per Single Track Kilometre (“STK”), although the Scottish Government is currently delivering projects in the range of £750k – £1.5m per STK. (Industry participants argue that this is the result of a rolling programme of electrification which allows experience to be developed and maintained.) For train services serving rural communities – which often have long lines and serve few passengers – the cost of electrification can be significant.

The two main alternatives to electrification are battery power and hydrogen powered trains. There is currently a trade-off between battery and hydrogen vs electrification: as they can run on non-electrified track, the former have low capital costs but higher running costs, whereas the latter has high capital costs but low running costs. Battery trains can currently reach speeds of around 75 – 100 mph, and hydrogen trains around 90 – 100mph. Battery power has the advantage over hydrogen in that less supporting infrastructure is required to be installed. However, with the caveat that battery technology is constantly improving, hydrogen powered trains can typically cover far greater distances without refuelling meaning that, for many rail services, hydrogen may be preferred over battery power. 

Given each technology’s respective advantages and disadvantages it is the view of industry participants that a mixture is required to be used to decarbonise the rail network – instead of being in competition, hydrogen, electricity and battery power can instead complement each other. For example, 15,400 STKs of the UK’s rail is currently unelectrified meaning that, to reach net zero, a choice has to be made between further electrification, hydrogen, or li-ion battery power. Network Rail currently proposes 13,040 STKs of further electrification, 1,300 STKs of hydrogen-fuelled services, and 800 STKs of battery-fuelled services, with a further 260 STKs where a choice has yet to be proposed. It seems that in reimagining transport in the UK, at least, all options are still open.

Hydrogen powered trains – where are we now?

While hydrogen is still a developing technology, there are hydrogen trains currently planned or in operation in rail networks across the world. Between September 2018 and May 2020 Alstom, the French transport manufacturing company, conducted a 530-day trial of its Coradia iLint hydrogen powered train on the German Weser-Elbe network. From 2022, it is intended that 14 Coradia iLint trains will begin replacing the existing diesel stock in Lower Saxony. Orders for the train have now been made in France, Italy and further tests have been conducted in Austria, the Netherlands and Germany. Alstom and British rolling stock company Eversholt Rail have also lead a UK pilot project to consider the feasibility of converting existing Class 321 trains to hydrogen (which they call the “Breeze” train).

Similarly, HydroFLEX is a UK-based hydrogen train scheme run by Birmingham Centre for Railway Research and Education (part of the University of Birmingham) and railway rolling stock company, Porterbrook. One of its goals is to retrofit existing trains with the necessary equipment to run on hydrogen. Its first successful trial test took place in September 2020, where a HydroFLEX train travelled from Quinton Rail Technology Centre to Evesham and back. HydroFLEX is now working on securing its technology to the underside of carriages, so as to increase space for passengers.

Scottish Enterprise and Transport Scotland are supporting the Zero Emission Train Project to develop the use of hydrogen trains in the Scottish rail network. It aims to operate a hydrogen train on a closed rail network for showcase at COP26 in November of this year.

Finally, the Swiss rail manufacturer Stadler has secured a contract from the San Bernardino County Transportation Authority in California to deliver the first hydrogen powered trains in the US.

Hydrogen for trains – the future

So, we currently have a fuel that could potentially compliment the use of electrification in decarbonising rail networks, yet green hydrogen is currently uneconomical which means hydrogen production necessitates some greenhouse gas emissions. Despite this, there are reasons to be optimistic about hydrogen’s future.

Firstly, the technology is in its infancy and often great improvements in efficiency and cost are generated as a technology matures and gains economies of scale. For example, battery prices are estimated to have fallen 89% in real terms between 2010 and 2020.

The International Energy Agency has stated that “hydrogen is currently enjoying unprecedented political and business momentumandwhat is new today is both the breadth of possibilities for hydrogen use being discussed and the depth of political enthusiasm for those possibilities around the world. Hydrogen is increasingly a staple of mainstream energy conversations in almost all regions”. In these circumstances and similar to the development of batteries, we are seeing economies of scale begin to develop in the hydrogen sector. The IEA notes that 10 years ago the majority of electrolyser projects were smaller than 0.2MW but that we now regularly see much larger projects such as ITEM Power’s Sheffield plant in the UK which is expected to produce 1 GW of hydrogen per year. Similarly, the IEA estimates that were governments to achieve their 2030 targets for the deployment of fuel cell vehicles, the cost of fuel cells could be reduced by 75%.

If we see wider-scale adoption of hydrogen, how would our transport infrastructure change? Well, initially there would need to be significant investment in the creation of new hydrogen-infrastructure or the retrofitting of existing infrastructure. The retrofitting of existing infrastructure is particularly interesting as hydrogen trains or vehicles do not take much longer to fill than diesel engines meaning that existing filling stations could be used. One advantage is that hydrogen may be able to be transported through countries’ existing gas distribution networks (which SGN’s H100 project in the UK aims to prove) so the congestion of transport networks may be improved. Alternatively, depending on how technology advances, electrolysers could be used to generate hydrogen on site at refuelling stations.

With regard to infrastructure, hydrogen trains have an advantage over hydrogen cars in that trains travel along a fixed track. This predictable path means that infrastructure can be installed with the certainty that the entirety of the route will be covered; unlike electric cars which are constrained by the availability of refuelling points. Similarly, as many train stations are proximate to bus stations, there is the potential for shared refuelling infrastructure.


Looking at the horizon, with the leaps and bounds battery technology has had over the past decade in mind, it may be that hydrogen becomes a fuel of choice for rail transport and even supplants electrification for some routes – becoming a vital part of transport’s route to net zero. There is reason to be cautiously optimistic about green hydrogen and, as a result, the decarbonisation of the rail network.

For more on the transport sector’s journey to net zero, see our other Law-Now articles here.

Our Road to COP26 Reimagined series looks ahead and anticipates the issues and opportunities that climate change presents across a number of sectors and areas that impact our clients.

At CMS, we put our clients’ world at the heart of what we do. For this reason, we have a team of lawyers from across the firm from a range of different expertise areas who are actively engaging with the issues and opportunities that climate change presents. Our aim is to help our clients to navigate this rapidly evolving legal and commercial landscape whilst also providing the interested with more information about this growing area via this Insight section.

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This Law-Now is part of our Road to COP26 series. We will be analysing and reporting on the implications of these events for the agenda at COP – look out for further updates on our legal insight on our climate change and sustainability pages.