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Cleaner power for rail’s future

August 11, 2017

Rolling-stock innovations are improving rail’s environmental credentials and its economic viability in a competitive transport landscape

Railways already offer favourable levels of energy efficiency and environmental impact, compared with other forms of transport.

But rising societal expectations, improvements in the carbon and energy footprints of other transport modes, and challenging government commitments mean the rail industry must continue to innovate to remain an environmentally sustainable and cost-effective form of transport.

In the UK, the government is aiming to reduce carbon emissions by 57% by 2030, compared to 1990 levels. Although rail accounts for less than one per cent of UK transport CO2 emissions, recent franchising competitions to run mainline passenger trains have included further energy efficiency and carbon reduction among their core requirements.

Lower CO2 emissions

Studies show that passenger rail generates approximately half the CO2 emissions per passenger-kilometre (pkm) compared to cars and a quarter of the emissions of air travel – but automotive and aviation are improving.  

UK passenger journeys have increased by approximately 70% over the past decade, while the number of trains in operation has grown by around 10%. In the same period, energy consumption and CO2 emissions have increased by approximately 12% overall. So, per passenger journey, energy consumption and emissions have reduced. Consistently, more people (and freight) travelling by train, instead of by car or plane, helps reduce energy and CO2 emission levels overall.

Powering rolling stock in future

Improving the energy efficiency and emissions levels of rolling stock reduces rail’s environmental footprint. Innovations in propulsion technology are one area of development.

Historically, trains have been designed to operate using a single energy source – usually diesel or electric traction.

Electric trains, commonly used on suburban commuter railways around the world, generate approximately 30% fewer CO2 emissions per passenger kilometre than diesels. However, electric trains require expensive infrastructure. In the UK, only 42% of the rail network is electrified and plans for extensions are not always regarded as value for money.

Diesel trains. Their self-contained engines offer greater operational flexibility, but they are generally more expensive to buy and operate. They also create local emissions and higher levels of noise, making them unsuitable for high-density suburban operations. 

Modern hybrid-propulsion technologies will become more common in years to come 

Jason Groombridge

UK Director, Rolling Stock

Bi-mode (or dual mode) and hybrid technologies are becoming more common in light and heavy rail. Using a combination of power sources – typically, electric traction and another power source – they give the benefits of electric traction while allowing operations on non-electrified route sections, where electrification costs are prohibitive. 

Bi-mode and hybrid solutions offer better energy-efficiency potential and operational flexibility for a given train performance than diesel trains, while hybrid systems incorporate energy recovery and storage to improve efficiency – as with hybrid cars. The energy storage devices (ESDs) are typically batteries, super-capacitors or flywheels.

Half of the new UK Intercity Express trains will be delivered as bi-mode vehicles, powered by a 25kV AC electrical overhead supply system, or by using on-board engines. Train operators TransPennine Express, Hull Trains and Abellio Greater Anglia in the UK have also ordered bi-mode trains – in total, more than 1,300 vehicles will be delivered over the next three years.

Modern bi-mode technologies are providing train owners with new opportunities for redeploying midlife rolling stock. Porterbrook, a UK rolling-stock owner, and Northern Rail, a UK train operator, are working with the Rail North Partnership on an innovative project to re-engineer Class 319 trains – displaced in recent UK franchise competitions – and convert them into bi-mode trains. This has the potential for a better environmental outcome by allowing these trains to be used in new ways, rather than be retired, and is a step towards the concept of retrofitting full hybrid technology to a midlife fleet.

There are plans to deploy hydrogen fuel-cell trains in Germany, and Alstom unveiled a mainline fuel-cell multiple unit, the Coradia iLint, at InnoTrans in 2016.

Hydrogen fuel-cell technology requires infrastructure to produce and distribute the hydrogen fuel, and is challenging to produce efficiently – but using renewable energy to produce it offers the opportunity to create a truly low-carbon-impact power system.

Battery technology is advancing and traction batteries are able to power trains at full operating speeds, offering zero-emission solutions on non-electrified routes. The independently powered electric multiple unit (IP-EMU) project was a recent, high-profile UK trial of a mainline train-battery propulsion system. It successfully demonstrated battery operation for a four-car multiple electric unit for distances of up to 50km. Meanwhile, the UK’s Birmingham tram is retrofitting traction batteries to its fleet, to enable wire-free operation in the city.

Super capacitors are an emerging energy-storage technology in rail, and have the advantage of being able to be recharged very quickly compared to batteries. In 2014, CSR Zhuzhou, China, started delivery of a 100% super-capacitor-powered low-floor tram. SNC-Lavalin’s UK graduate trainees have developed their locomotive entry for the national Railway Challenge to operate on super-capacitor technology.

Lowering environmental impacts

Reducing train weight is another approach that helps cut energy usage and carbon emissions. Innovations in structural design and materials are areas of development getting real-world applications in rail systems. Reducing train weight lowers the energy required to propel it, and has the potential to reduce track wear and associated costs. Benefits are greatest for trains on frequent-stopping services, such as metro and light rail systems.

Technology developments helping trains operate more efficiently are also playing a part. Driver Advisory Systems (DAS) and Connected-DAS (C-DAS) technologies supply real-time information and guidance to train drivers about speed and braking, to enable an optimal balance between energy usage and timetable compliance. The UK Rail & Transit team has developed and deployed a system that is now in use with several operators, including Virgin East Coast – operating between London and Scotland – and c2c, a London commuter operator.

Finally, measuring energy usage – and charging train operators for actual energy used through accurate metering – is a key element in an overall approach to reducing energy and carbon footprints in rail. The UK’s rail infrastructure owner, Network Rail, uses SNC-Lavalin’s Energyx software to measure electricity usage on several passenger fleets click here.

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