HomeElectrificationWhy electrify?
Listen to this article

Many within the rail industry feel that the recent electrification cutbacks were a mistake as, to quote the RDG’s long term passenger rolling stock strategy (LTPRSS), “over time, electric trains have generally proved to be more reliable, efficient, environmentally friendly and cheaper than those powered by diesel engines”.

Yet, even when carried out in a cost-effective manner, the price tag for route electrification is measured in billions of pounds. Government has a responsibility to ensure that such large sums are spent wisely and so was right to re-consider the case for committed schemes as the costs of electrification projects more than doubled.

The resultant cancellation of previously confirmed electrification schemes was partly due to the ability of new bi-mode trains to operate in both electric and diesel modes (issue 157, November 2017). As a result, Government considers that passenger journeys can be improved sooner than expected by these “state of the art trains” that “can improve journeys for passengers instead of carrying out electrification works”.

In this article we examine whether this means that electrification is no longer necessary.

Hitachi Class 800 at Paddington.

Mini power-plants

Eleven years ago, the government of the day was not in favour of electrification and also felt that developments in train technology made it unnecessary. In response, a joint Network Rail/ATOC (Association of Train Operating Companies, now subsumed into the Rail Delivery Group) later stressed the benefits of electrification including pointing out that it was wasteful to use diesel trains as “mini power-plants”. It is also the case that the power output from such on-train generation will be less than an electric train due to weight and space limitations, including the large volume needed for the cooling group of a powerful diesel engine.

At full power, the overhead line supplies a nine-car electric Pendolino train with about 6MW (equivalent to the amount of power needed to supply six thousand homes). 5MW are needed to power the train with a further megawatt or so suppling auxiliary machines and the train’s hotel load.

A nine-car bi-mode train has five underfloor diesel engines with a total power output of 3.5MW, of which about 2.8MW is available to power the train. When these trains operate in electric mode they draw 4.5MW of traction power from the wires, sixty per cent more than in diesel mode.

Despite this, the Government claims that electric trains offer “no obvious passenger benefit” over the less powerful diesel bi-mode.

Within the DfT, there is a perception that, even if it were possible to justify electrification for high-speed trains, it is not necessary for slower trains. This is wrong, as electrification offers not just higher speeds but higher acceleration. A Class 380 electric multiple unit can accelerate to 60mph in about fifty seconds, compared with one minute fifty seconds for a Class 170 diesel multiple unit. For this reason, electrification offers significant reductions in journey time on routes with frequent stops.

A 700kW diesel engine power pack for a bi-mode train.
A 700kW diesel engine power pack for a bi-mode train.

Cheaper to run

Electric trains are significantly cheaper to operate and maintain, as well as being more reliable. The LTPRSS shows that modern EMUs (36,805 MTIN or Miles per Technical INcident) are more than twice as reliable as modern DMUs (15,971 MTIN).

An indication of the additional maintenance cost of a diesel-powered fleet is given by the differing procurement costs of the Great Western and East Coast IEP fleets, which include a 27-year maintenance contract. The Great Western IEP fleet costs £4 million per coach more than the electric East Coast one, mainly because it operates more miles in diesel bi-mode. Thus, the additional diesel maintenance cost of the 369-vehicle GWML bi-mode fleet is around a billion pounds over the period of the maintenance contract.

Diesel fuel is also significantly more expensive than electric traction, in part because electric trains can recover the huge amount of energy generated during braking back into the wires. A recent ORR report showed that diesel fuel accounts for 40 per cent of Virgin West Coast’s traction cost, despite only 15 per cent of its fleet being diesel-powered.

Network Rail’s RUS (route utilisation strategy) for electrification, published in 2009, concluded that diesel fuel cost is generally 19 to 26 pence per vehicle mile greater than electric traction. For the GW bi-mode fleet, which will run about a thousand miles a day with perhaps half of that in diesel mode, this is an additional fuel cost of around a third of a billion pounds over the 27-year maintenance period.

Decarbonisation challenge

In February, Transport Minister Jo Johnston called for rail industry proposals to remove diesel-only trains from the rail network by 2040. Bi-mode trains were thus exempt from this requirement. These are considered to be a “great bridging technology to other low emission futures.”

Johnston considered that, as battery technologies improve, he expects to see the diesel engines in bi-modes replaced altogether and that perhaps both batteries and diesel engines will be replaced by hydrogen units.

The IPEMU (independently-powered EMU) trial in 2015 was described in “Batteries included” (issue 125, March 2015). This used a four-car EMU that had a 7.2 tonne, 424kWh battery pack fitted under one coach (pictured above). Running under electric power for seventy percent of the time was sufficient to provide a battery charge that provided performance comparable to an EMU over 77 kilometres.

Thus, the trial demonstrated the feasibility of using batteries to power a train for short distances off the electrified network, although cost comparisons with a diesel power pack have yet to be published. However, the use of batteries to power a train beyond electrified wires for much longer distances, such as Kettering to Sheffield and back (305km), would require the development of batteries with a much higher energy density. It is wrong to plan transport policy on such an unpredictable development, which, even if possible, could be many years away.

Hydrogen has been shown to be a viable traction technology for medium-range applications. However, it has a low efficiency. When produced by electricity, hydrogen trains require around 3.4kW to deliver one kilowatt of traction power. If electricity is fed directly into a train, only 1.2kW is required.

Like batteries, hydrogen also has a low energy density, which is a tenth that of diesel. For this reason, Alstom’s hydrogen powered iLint (pictured below) has the entire roof of each vehicle taken up with hydrogen tanks and fuel cells. This gives it a range of 700 kilometres at speeds of up to 140km/h. Hence hydrogen cannot be used for long-distance high-powered trains unless passenger space is sacrificed to provide more space for its tanks and fuel cells.

Hydrogen traction equipment consists of fuel cells, a traction battery and traction converter. Incorporating this, and the hydrogen fuel tanks, into a train requires it to be built around this equipment. This is another reason why Johnson’s vision that bi-mode trains are a bridging technology in which diesel engine power packs can be replaced by hydrogen units is unrealistic.

Electrification should be the answer

For the foreseeable future, the only viable self-powered rail traction technology for high-powered, high-speed trains is the diesel engine. This is particularly true for freight trains that require “mini power-plants” of around 2.5 MW.

Thus, the only possible answer to Jo Johnson’s call to decarbonise the rail network is further electrification with the use of hydrogen and batteries on branch lines and rural routes. Electrification eliminates pollution at point of use and offers potential carbon reductions by enabling rail traction to be powered by renewable energy sources. It also reduces dependence on fossil fuels that, in the future, could become increasingly costly due to pollution taxes and shortages of supply.

A further consideration is the impact of the cancelled electrification schemes on the rolling-stock cascade. The LTPRSS forecasts that, by 2029, the revision of the electrification programme in England and Wales will require an additional 500 self-powered vehicles. At the same time, large numbers of surplus EMUs will be scrapped. It is doubtful whether the cost of these additional vehicles was considered before the decision to cancel electrification schemes was taken.

This raises the issue that electrification would be a government-funded investment, whilst the more expensive rolling stock needed to avoid electrification is procured from private finance. This was no doubt a further government consideration.

As always, there are lessons from beyond the English Channel where the benefits of electrification are recognised by many countries that have a high percentage of their rail network electrified. These include Netherlands (76%), Italy (71%) and Spain (61%). In the UK, 42 per cent of the network is electrified.

Although there are strong arguments in favour of electrification, its case is significantly weakened by high project costs. Hence the industry needs to convince the Government that it has learnt lessons from over-expensive projects and can now deliver electrification at an affordable cost. If not, it is unlikely that there will be any significant increase in the UK’s electrified network for the foreseeable future and we’ll all just have to live with resultant increased costs and unrealised passenger and environmental benefits.

Further information about the business case for the electrification of UK railways is available at the website of the campaign to electrify Britain’s railways www.railwayelectrification.org.

Read more: Getting electrification right


David Shirres BSc CEng MIMechE DEM
David Shirres BSc CEng MIMechE DEMhttp://therailengineer.com

Rolling stock, depots, Scottish and Russian railways

David Shirres joined British Rail in 1968 as a scholarship student and graduated in Mechanical Engineering from Sussex University. He has also been awarded a Diploma in Engineering Management by the Institution of Mechanical Engineers.

His roles in British Rail included Maintenance Assistant at Slade Green, Depot Engineer at Haymarket, Scottish DM&EE Training Engineer and ScotRail Safety Systems Manager.

In 1975, he took a three-year break as a volunteer to manage an irrigation project in Bangladesh.

He retired from Network Rail in 2009 after a 37-year railway career. At that time, he was working on the Airdrie to Bathgate project in a role that included the management of utilities and consents. Prior to that, his roles in the privatised railway included various quality, safety and environmental management posts.

David was appointed Editor of Rail Engineer in January 2017 and, since 2010, has written many articles for the magazine on a wide variety of topics including events in Scotland, rail innovation and Russian Railways. In 2013, the latter gave him an award for being its international journalist of the year.

He is also an active member of the IMechE’s Railway Division, having been Chair and Secretary of its Scottish Centre.


  1. Great article and one a message that main stream media should adopt. The benefits of electrification also extend to far better refinement of the passenger experience.

    Why on earth commit to electric traction for road, which does not have a easy mechanism for electric connection, but not for rail which does?

  2. Can batteries be used to bridge ‘expensive to electrify gaps’ in a cost-reduced electrification scheme?

    I.e., instead of electrifying 100% of a line, you electrify 80% that is easiest to electrify, and rely on batteries for the parts that are expensive to convert.

    Obviously, this is only valid if line electrification follows something like the 80:20 rule (or 70:30), i.e., 70% of the route costs 30% to electrify, the other 30% is what makes it costly and gets these things cancelled.

  3. Is it fair to compare the running costs of electric versus diesel trains without including the substantial running cost of the rail electric infrastructure & also the high costs incurred when the wires come down, a frequent event UK wide ?

  4. At least Network Rail are electrifying the Taunton line as far as Newbury and between Manchester and Preston via Bolton. Since they completed the electrification on the Blackpool North Line, Edinburgh-Glasgow vis Falkirk Line, Gospel Oak-Barking Line, electrification to Bromsgrove and Lickey Incline between Walsall and Lichfield Trent Valley.

    • Sorry between Walsall and Rugeley Trent Valley. And yes between Barnt Green and Bromsgrove. As the electrification in the West Midlands is to be completed this year.

  5. Also why not electrify between Coventry and Nuneaton and to allow a 2tph service between Coventry and Nuneaton using some of the Class 350’s instead of Class 172’ that could be ideal to operate between Coventry and Leamington Spa as Kenilworth station has reopened.


Please enter your comment!
Please enter your name here

This site uses Akismet to reduce spam. Learn how your comment data is processed.