Trains used to be relatively simple. Either they ran off electricity from an overhead wire or a third rail.. or if the track didn’t have wires or third rails trains ran on fuel instead.. burning either coal or diesel.

Electrifying operational rail lines for traditional electric trains is fiendishly expensive. Which is why we’re providing an overview here of a whole suite of new ways to power trains, that can put electric trains on un electrified tracks without burning fuel.

We have used a generous helping of Chat GPT and Grok AI generated images to illustrate this article.

While many busier parts of the UK Rail network are electrified only a tiny 38% of track is ready to run electric trains compared to a European average of 56%. So over 60% of UK track is only currently suitable for diesel burning trains.

How diesel is the UK Railway?

Well we know the proportion of track that is electrified but in passenger journeys and emissions things might look better as the busiest routes with the most services and passengers tend to be electric. We haven’t found ideal stats but the UK Office of Road and Rail Environment report shows the UK in the year to March 2024 shows UK Rail used

• 3.894kWh of electricity.. equivalent to driving 15.576 billion miles (25.122 billion km) in an electric car at 4 miles per kWh.
• 557m litres of diesel which if you burnt that in a diesel car at 40mpg would take you.. 4.9 billion miles (7.903 billion km)

which gives a very rough equivalent value for fuel usage.

CO2 Emissions from UK trains

Passenger trains accounted for 1,917 kilotonnes, with the remaining 440 kilotonnes from freight trains.

Looking at Table 6100 – Estimates of normalised passenger carbon dioxide equivalent (CO2e) emissions the emissions per vehicle km on UK electric passenger trains has fallen from 843g in 2011/12 to just 359g in 2023/4. By comparison CO2e for per vehicle km on diesel trains is 1402g… 3.9x worse and it’s not improving. The combined average is 628g.

For emissions per passenger km the combined figure is 31.3g. It’s not perfect but applying the per vehicle factors above for electric trains the per passengers km is 18g (and falling each year) while each passenger km on a diesel train likely emits 69.79g per passenger km which remains constant (they are the same now as in 2012)

Cost of Fuel burning trains

Diesel burning is a problem from several perspectives

• a fuel burning network is a climate emissions disaster with no improvement ever
• trains that emit high levels of pollution in stations, in depots, tunnels, in passenger carriages and close to railway track are a public health disaster including triggering many cancers, heart disease, Asthma etc. We cover this in an earlier article here on why diesel trains need to be replaced.
• Financially they are a disaster too, costing far more in maintenance and in (imported) fuel to burn and they are less reliable too.

We have slightly enhanced this AI picture of the iconic Intercity 125 to neatly illustrates a major health issue for passengers in diesel trains. The toxic exhaust flies out of the top of the locomotive and then every passenger carriage has air intakes perfectly lined up to suck in the toxic exhaust gases and particulate.

Fuel burning trains in UK

Diesel

Car equivalent

A diesel car or van

What is it

Fuel burning engines power a train by diesel into CO2 and toxic gas and particulate.

Air Pollution

Absolutely massive whether you are in a station, on a train or anywhere near a rail line. Diesels produce far more toxic gas and particulate than any form of powering vehicle other than fuel used for shipping including ferries and cruise liners. Diesel trains also produce high levels of particulate of all sizes. Clean air regulations on the railways are close to non existent and many diesel locomotives are so old that even those regulations don’t apply to them.
Toxic pollution from brake dust is also maximized as there is no brake regeneration

CO2

Diesels trains run off fossil fuel and produce large amounts of CO2.

Diesel Electric

Car equivalent

Much like mild hybrid MHEV diesel cars they can’t travel a single centimeter on electric drive alone.

Air Pollution

As bad as a standard diesel electric trains have run for many decades and presumably provide some limited efficiency benefits and torque from electric drive motors for pulling heavy loads without lots of gears but essentially are just as polluting as a standard diesel.

CO2

Diesels-electric trains run entirely off fossil fuel and produce large amounts of CO2

Electric with diesel bi mode

These are electric trains that use a diesel engine on sections of unelectrified track. Frankly a rather strange and dirty way to power what is essentially an electric train. 

UK Example – Great Western Railway

A particularly crazy installation is on the costly £2.6B UK Great Western route where the 128 mile route is mostly electrified except for 18 miles in the cities of Bath and Bristol. It runs 90% of the route on clean electricity then switches to highly polluting diesel mode in cities with high population.

Air Pollution

Bad – it has no battery range you don’t get the benefit energy regeneration from braking and can only use electric power on electric track. Particularly disappointing is that in testing by the RSSB the Great Western Hitachi bi mode trains actually had worse levels of air pollution in the carriages than many completely diesel trains.

CO2

Performs better here because most of the route runs on electricity than can be largely or entirely from renewable energy. It is compatible as a step towards a zero net carbon economy but far too expensive for only a partial step.

Diesel with battery bi mode (short range)

Car Equivalent

This operates much like a diesel Prius hybrid SUV car. They can travel short distances in EV mode and get some energy regenerated into the batteries when braking.

Clean air

It is likely to be as toxic as a diesel for 90% of the time, it does have one advantage. You can choose where you run the diesel engine and in theory could run entirely in electric mode in and around stations. You can therefore choose where you render the air toxic – in less populated areas with low background pollution. Brake energy recuperation did also cut brake dust.

The same approach is being trialed for shipping allowing ships to switch off their engines when in or close to port.

UK Example Chiltern Railways

When the hybrid system detects proximity to stations or depots, it will turn the engines off and run on its battery, removing gas and noise emissions from populated areas. 168 HybridFlex train is due for completion by late 2019 and will serve passengers on Chiltern Railways routes, including commuter routes between London Marylebone to Aylesbury.

After a big song and dance about how this technology would cut the terrible pollution at Marylebone Station, Chiltern railways delayed introduction to 2030, introduced a single working train (an adapted 20 year old diesel train) then quietly scrapped the whole plan in late 2023 replacing it with a vague promise to look at greener trains one day. The planned battery range was… just 1 mile! It was probably primarily designed as a greenwashing exercise and to reduce noise and obvious exhaust at stations to give the appearance of a cleaner train. Pollution levels inside the passenger cars would have been nearly as bad as pure diesels.

Toxic pollution from brake dust is somewhat reduced as there is a small amount of brake regeneration

CO2

Very small reductions if most acceleration out of stations can be on electric drive. It is not compatible with a zero net carbon economy but is a relatively cheap way to cut the number of people exposed to air pollution in the short term.

Diesel with battery and diesel tri mode (Medium range)

Car Equivalent

An BMW i3 rex diesel with inductive charging on sections of road

What is it

Honestly this is an electric train with batteries for unelectrified lines.. and an additional diesel engine to re charge the battery in case it runs out of range!

UK Example – Wales Rail

Wikipedia summarize this as “The British Rail Class 756 FLIRT^[7] is a class of tri-mode multiple units built for Transport for Wales Rail by Swiss rolling stock manufacturer Stadler Rail“.

Yes you guessed it.. this was probably ordered by someone who drives a Mitsubishi hybrid.. it’s an electric train that has a battery… but.. wait for it.. has a whopping great diesel power car in the middle in case of range anxiety. Maybe that’s harsh and a bi Mode battery electric would not have enough range yet but it’s definitely a niche solution.. a electric train carrying batteries when running on diesel and carrying a diesel engine when running on battery. Battery range is about half the usual at around 40 miles.

CO2 and Air Pollution
This could be anything.. like a plugin hybrid they could shift to diesel (with regen) every time they run off the electrified track or run mainly on battery but occasional diesel for a stretch the battery can’t manage. Hopefully it will cut the amount of diesel burnt a lot but it all depends on the route and the operator. At least the charging should be automatic.. unlike most plugin hybrid cars that fail to cut fuel burning at all because most drivers never plug them in.

Cleaner train technology

The very very long history of battery electric trains

You might be convinced that battery powered trains are some new fangled eco technology that will never catch on… wrong. In fact Germany ran battery powered passenger railcars, largely on branch lines from 1907 until 1995. New Zealand had one in 1926. The website Loco Info lays out some of the history here along with some video footage.

This historical film also shows ETA 150’s in service in Germany between the 1950’s and 1990s. DC motors were very noisy then.

DB Class ETA 150 Battery electric train
Top speed 62 mph. The claimed range was a staggering 190 miles, more than double that of new models.
DB Class ETA 150 built in 1957 retired in 1995. Wikipedia “very comfortable to travel,in, quiet, rode well on the rails owing to the weight of the lead acid batteries, and were pollution-free (no smoke or fumes) 

1 Electric trains from overhead cables or third rail

Car equivalent

Bumper cars at a fairground taking power from the roof

What is it

This sounds so simple. You generate clean power and the trains run on it. If you are a country like Switzerland that electrified all its railway nearly 100 years ago it really is a brilliant way to run a clean efficient railway directly from renewable energy. On major new railway lines it also makes great sense.
Where it falls completely flat is as solution for replacing diesel on existing lines. The costs are too high for it to be a rational alternative. Any country trying it would be likely to give up along the way. It is no solution if it isn’t complete like the Swiss Network. 

UK Example Great Western Railway Electrification

The UK is pretty much bottom of the international league table for delivering large scale infrastructure on time, on budget or efficiently on a remotely reasonable cost. Even by UK standards this project was outstandingly poor.
The project involved adding overhead wires to an existing railway line while leaving it running most of the time. As a result engineering teams could only work for about 3-4 hours a night while the original cost estimates ballooned from around £700m to £2.8B when they realised that the height of bridges and tunnels on the route needed to be raised. It’s been known for some time that the height of a pure electric train and it’s overhead wires is taller! In the end it cost about £23.6m a mile to electrify and even then they had to leave out 18 miles of the 128 and so had to order electric trains with.. a diesel engine for these sections. On the plus side this has pushed the UK to become a potentially massive market for trains that can reduce this cost or don’t require overhead wires at all.

Air Pollution

Low – one disappointing aspect is although there are no exhaust emissions from running the train most pure electric trains use only friction brakes which lose energy and create big emissions of brake dust. The technical solution to recuperating this energy involve either batteries or major upgrade to the trains and the power supply to enable it to cope with power being pushed back when trains brake. It will be sorted but isn’t without challenges.

2 Electric with battery bi mode

Car equivalent

A fully electric car that can top up using inductive chargers under the road.

What is it

Essentially this allows a train to run clean everywhere either on electrified line or by travelling between electrified sections on battery power. This arrangement could be used to replace the electric trains with diesel bi mode.

UK Example – Merseyrail

The Swiss made Stadler 777 trains have been in service since 7th October 2023 including the BEMU (battery electric multiple units) serving new unelectrified stations like Headbolt lane.
Using a 320kWh battery (equivalent to just over 4 Tesla Model 3’s) it has a nominal range of 34 miles but achieved up to 84 miles in testing.
Teething issues have mainly revolved around buggy Swiss software which is taking a long time to iron out. Hardware seems to be fine as far as I am aware.

There are other electric with battery bi mode trains rolling at in the UK including the new London Piccadilly line tube trains which will have enough power to reach the next station while some Birmingham trams can serve line extensions that have no power supply.

Other Examples

• UK – Hitachi rail is leading a new public-private partnership to develop next-generation battery technology for intercity and commuter trains. They will use lighter more energy dense batteries off the back of developments in automotive battery tech.
• UK – Angel Trains, Hitachi Rail, and TransPennine Express have announced the success of the UK’s first intercity battery train trial in the North of England
• Ireland – Alstom has received an order for 185 Dart+ electric and electric with battery bimode carriages with the intent to order 750 carriages over the next 10 years.

Advantages

• Electrifying existing running railway lines is prohibitively expensive but these trains with significant battery power (current range around 60-80 miles) can be charged on the move and from brake regeneration and allow electric trains to go to a destination without electrified track
• This allows you to electrify the easy or cheap sections of track where there are no bridges, junctions and tunnels that drive up costs massively. Ie it’s a bit like skipping the bits of homework you don’t like and doing the easy parts. It also allows electric trains to service unelectrified branch lines massively cutting the cost of expanding a rail network.
• Another advantage is it allows more flexibility on finding optimal locations to connect to the electricity grid – something that often delays projects in the UK.
• With batteries getting cheaper and more energy dense every year the economics tilt further in it’s favour each year especially combined with high efficiency and low running costs.

These trains are likely to become the main alternative to both complete electrification and hydrogen. Whether it succeeds rather depends on how much track has to be electrified for batteries to recharge on the move. If you could electrify under 30% of your railway line and still have batteries fill in the gap on efficient renewable energy then this technology is likely to go mainstream

Rightly or wrongly I believe these trains should be able offer 2 or even 3 times their current range in the next 5 years. Indeed Great Western Railway in collaboration with Hitachi and Eversholt rail are aiming to introduce battery electric trains in the 2040s to cover the entire 300 mile (483km) distance from London to Penzance. This could be battery range alone but it would make sense to have trains capable of an operational 150 miles and have a few sections of electrified track en route to top up. This would also save on needing a massive charge while stationary at the end of each journey.

Air Pollution

Very low. No exhaust emissions and braking uses a lot of regeneration cutting brake dust.

CO2
Highly efficient and run off an electricity supply which in the UK should be 100% carbon free by 2030. The regenerative braking saves a vast amount of energy too.

3 Battery only

Car equivalent

a battery electric car

What is it

Battery only trains charge slowly overnight in a depot or rapid charge only while in a station – usually a terminus on a local route. It then runs the service on that charged battery.

And yes these really exist. They aren’t going to solve the replacement of diesel on many routes but they do work. Just have a look at the specs of these battery only railcars from Germany built in the 1950s! Some had a range of 190 miles using just lead acid batteries.

This strongly suggests that new trains with

• modern batteries
• more aerodynamic shape
• regenerative breaking should be doing much better than the 60-80 mile range they offer today.
• Modern trains are heavier but trains are much less affected rolling resistance (around 5x less) so with good regen should be far less affected by weight than road vehicles using tyres.

4 Hydrogen

Car Equivalent

A Toyota Mirai FCEV

Why Hydrogen should be a winner against batteries

• Projects…Look at the number of hydrogen research trains government funding and trial services it must be a winning technology.
• Range…You might also be impressed with the Guinness world record distance travelled without refuelling a hydrogen train. It covered 1,741.7 miles non stop in 46 hours suggesting a speed around 39 miles per hour. Coincidently the battery model of the same Swiss Stalder Flirt train holds the battery train record..136 miles
• Refuelling speed.. just swap out your diesel tanks at depots with hydrogen and off you go. No grid connections, no waiting around.. job done.
• Green trains just emitting clean water vapour running on hydrogen produced from renewable electricity seem to seal the deal.. surely hydrogen must trump battery and electric/battery bi mode trains?
• Train Manufacturers often offer the same models in hydrogen or battery versions so lot’s of choice

Why the role for hydrogen will be limited

Michael Liebreich a leading expert on use of hydrogen summarises the issue well.

Like a Swiss army knife you can indeed do all sorts of things with clean Hydrogen…but like a Swiss army knife there is almost always something cheaper, safer and more convenient. It will only be used where it is cheaper, safer or more convenient, and it never is, or where there is no alternative”

Michael Liebreich does a great job of covering the issues so I would recommend watching here.

If you don’t, in summary hydrogen is too complex and too costly to:

• produce
• transport
• store
• and to use for most use cases
• It also has significant safety risks to mitigate adding more cost

Using hydrogen on a train or any EV is about taking electricity, converting it to hydrogen till you need it, then converting it back to electricity to drive the vehicle. If you take the same 100kWh of electricity and put it in a battery electric vehicle about 27kWh will be wasted and 73kWh will be used to drive the wheels. Use hydrogen as the medium and just 22kWh will drive the wheels and 78% will be lost. So starting with the same amount of electricity a battery train will cover more than 3x the distance.

Hydrogen wins on lobbying and deflection

Keep looking at the shiny hydrogen train… it’s silent and smooth (because it’s an electric drivetrain) and has a longer range. It comes with lots of grant funding, sometimes making them completely free to the operator.

What the manufacturers won’t mention is..

• The market price for hydrogen costs way more than any other option to run
• supplies are erratic and limited and around 99% comes from fossil fuel sources that often are actually worse for climate change than diesel.
• The infrastructure and trains are much less reliable than electric or battery

The result is there are lots of introductions ( the fossil fuel industry uses hydrogen tech to delay electrification) and trials of hydrogen trains but follow up orders are relatively few and where they have got to enter service it has so far been a bit of a disaster.

Germany examples – the great hydrogen experiment

Lower Saxony – EVB/ LNVG

• 2022 – 14 brand new Coradia iLint hydrogen trains were introduced in 2022 to run local services. If you search for “hydrogen trains” you will see their blue livery. They are the poster child for a hydrogen train future.
• 2023 Having used the hydrogen trains for a year, Lower Saxony decided that all other diesel services would be replaced by 102 battery electric bi mode trains and 27 pure electric trains because they are cheaper and better. Having tried hydrogen not a single further hydrogen train will be ordered.
  2024 – they were struggling to get supplies of hydrogen resulting in half of services returning to diesel trains. It turns out that this was caused by an explosion of one of the trucks used to transport hydrogen at Linde. It resulted in shortages for use in trains and also at hydrogen filling stations across Germany lasting months!

Taunus line

• The world’s largest Hydrogen only trainline has had major technical problems which cancelled 19% of services in 2023
• in 2024 the line had to be closed completely because of technical problems with its 27 hydrogen trains. They worked for a bit in the summer then started to go wrong again. They were then replaced by diesel trains which also had technical failures and had to be replaced by.. a bus service. All will now be taken out of service for the whole of 2025 and replaced by rented diesels. The Frankfurt region is threatening to return all the hydrogen trains.
• problems were compounded when 20 of 60 drivers resigned blaming the stress of operating the unreliable hydrogen trains.

Baden-Württemberg

Hat’s off to this German region that decided to do their homework before ordering hydrogen trains. On hydrogen they concluded

• Advantages
  minor impacts upon introduction and during operation
  no changes required to the rail infrastructure
• Disadvantages
  costly filling infrastructure
  low efficiency and high energy consumption
  high cost of hydrogen
  limited availability of green hydrogen – 99% comes from fossil fuel currently
  need to continually resupply the hydrogen filling stations with diesel lorries
• Cost – over 30 years on the 2 lines evaluated the electric and battery electric options were between 30% and 81% cheaper.

This article from cleantechnica details the in service issuers with hydrogen trains around the world including links.

So which technology will replace fuel burning trains

Both battery, battery electric bi mode and hydrogen trains are able to replace diesel without prohibitive costs of electrifying entire lines.

Range is still in hydrogen’s favour but as battery range increases less and less and less track would need to be electrified to run a battery electric service. This is another problem for hydrogen. In cost and capability hydrogen is just not progressing fast enough to make it more competitive. In fact the lead for battery technology grows with every passing year with battery costs falling fast, range and energy density increasing and charging speed increasing to the point where it seems likely a Chinese EV will manage a 10-80% charge in under 10 minutes, using both NMC and even LFP batteries in 2025. (April 2025 Update – BYD is now able to charge in 5 mins while several brands have got down to between 9.5 and 12 minutes.

Every rail line is different and will have different access to electricity grid connections. Even if we assume that battery electric train range will increase rapidly from 80 miles to say 200 miles, and even if battery electric trains become ever more effective at regenerative braking to offset routes with big climbs and descents there will be some routes where hydrogen trains could be the only option.

For remote, low use and long distance passenger rail lines where it makes sense to charge at the start or end only, hydrogen might make sense. That said lighter and more efficient battery trains may be able to step in to enable battery trains to cover the distance too. I can also imagine that long distance very heavy freight trains as used in parts of North America could also a market.

In the UK apart from a few experimental heavily subsidised schemes hydrogen trains will likely be a non starter even before you ask yourself… is hydrogen a green fuel? It’s worth also noting that total hydrogen supply is small and growing slowly. There are lots of uses of hydrogen where it is actually the only option. Using it in heating or transport is a waste.. like only bathing in Veuve Clicquot Champagne. You can do it but it makes no sense.

What is exciting is that there are now good solutions to get electric trains onto unelectrified track and in 10 years they will be cheaper and better still.