Electrification of rail
Trains use locomotives or railcars that convert energy into motion to pull or push cars along tracks. Many fuel sources have been used to power the engines, but today most train engines use electricity or diesel. Electric trains have no direct (tailpipe or tank-to-wheel) CO2 emissions, whereas diesel trains produce CO2 and other pollutants through fuel burn. Electric trains may, however, be the source of so-called upstream or well-to-tank emissions (i.e. stemming from electricity generation and distribution). The degree of such emissions depends on the energy sources used for electricity generation.
Electric trains can recover energy when they are braking, as electric motors may act as power generators. Up to a third of total traction energy can be recovered through this “regenerative braking”, further enhancing an electric train’s energy efficiency. The recovered energy is typically used to supply power for lighting or other on-board needs. It can also be used by the following train or stored for later use if the network infrastructure allows for electricity storage.
Capital investment is required to electrify railway lines for electric trains. For rail lines with high levels of traffic, the much lower operational cost of electric trains can balance the high infrastructure cost associated with electrification.
Electrification of rail removes all direct (tank-to-wheel) CO2 emissions and other pollutants produced by rail. Diesel, the common alternative power source for trains, emits between 6 and 30 grams of CO2 per passenger-kilometre. (Values depend on the train’s engine efficiency and load factor, and thus can vary considerably.)
Upstream CO2 emissions from electric train use depend on the energy mix of the country where the train is operated.
It is worth mentioning that electrification of rail, like any infrastructure development, causes CO2 emissions in the infrastructure development phase.
Electrification of rail has high infrastructure development costs. It requires building new rail lines or adding infrastructure to existing lines to provide trains with continuous electricity. This can be done by either overhead power lines or a third, electrified rail.
The cost of electrifying railway lines depends on multiple factors, but studies quote a range of EUR 0.5 million to EUR 2 million per kilometre. Factors affecting the cost include track characteristics and whether the track will be used by high-speed rail.
Electrification of rail reduces emissions of GHGs and local pollutants from the former diesel engines.
Energy recovery through braking reduces the amount of energy needed to operate the train: regenerative braking can convert up to a third of total traction energy to electricity.
With their much higher energy efficiency and lower maintenance needs, electric trains have significantly lower operational costs – as little as a quarter of those associated with diesel trains.
ITF (2021) Transport Climate Action Directory – Electrification of rail
https://www.itf-oecd.org/policy/electrification-rail
Douglas, H., Roberts, C., Hillmansen, S. and Schmid, F. (2015) An assessment of available measures to reduce traction energy use in railway networks. https://www.sciencedirect.com/science/article/pii/S0196890415009759
Givoni, M., Brand, C. and Watkiss, P. (2009) Are Railways Climate Friendly? https://www.researchgate.net/publication/263145479_Are_Railways_Climate_Friendly
IEA (2019) IEA Mobility Model. www.iea.org/topics/transport/mobilitymodelpartnership/
IEA (2019) The Future of Rail. https://www.iea.org/reports/the-future-of-rail
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