while not null: Speed vs energy use in high-speed trains, or how fast is too fast?

This blog sat in draft for a long while now. It's not finished - I'd like to do more comparisons between existing boxy trains, and new aerodynamic high speed trains, but I also don't want to keep it in draft any longer. This is a very interesting, but also a complex subject with source data often being proprietary (hidden) or hard to calculate.

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You may have seen arguments similar to this one:

We should be investing in regular trains, not high-speed trains, because high-speed trains cost too much to run, because their energy use increases exponentially with speed. A train going 2x faster, for example 320 km/h vs 160 km/h uses 4x more energy.

This got me interested. Is this true? How much energy are we talking about? How do different trains compare?

There is also another argument against going fast: the increased wear and tear of the electric engines, wheels, bogies, rails, sleepers, traction.

There are also costs of track design: turns have bigger radius, switches have to be longer.

There is also noise.

I will concentrate on energy consumption.

The simple answer is: the first statement above, as a whole, is not true. It's true that the aerodynamic drag force increases with the square of the speed, but, just like with cars, train designers can improve the drag coefficient to make a train going faster use less energy than another train going slower. An old boxy train going 160 km/h can use more energy than a new, streamlined train going 320 km/h. There are also other factors that determine total energy use on the same route, with the same electrical system, the same atmospheric conditions: mass of the train, number of stops, acceleration, and even more factors that determine the final cost to the operator: number of passengers, cost of electricity - highly dependent on time of day (electricity can be practically free or even have a negative price during the day because of solar generation), line capacity, and even more factors that determine the cost/benefit to the society as the whole: alternative costs vs car or air travel, economic development, greenhouse emissions, particle matter pollution, impact on ecosystems.

A 2008 "Increasing energy efficiency of rail transport" article by Adam Szeląg (Adam Szeląg - IEEE Xplore Author Profile), a professor with the Electrical Engineering Department, Electric Traction Division, Warsaw University of Technology:

For example, analyses carried out by Spanish railways [22] regarding energy consumption by a locomotive train (weight 300 t) with a power of 5.6 MW, powered by a 3 kV DC network on a 442 km section (average speed 151 km/h) and a high-speed HST (weight 400 t) with a power of 8 MW (average speed 232 km/h) gave quite surprising results – the locomotive train consumed 9.41 MWh, the high-speed train – 7.93 MWh (approx. 15% less) of energy taken from the traction substation.

https://bibliotekanauki.pl/articles/253733

https://bibliotekanauki.pl/articles/253733.pdf

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https://infrastructure.aecom.com/transportation/how-fast-is-too-fast-for-high-speed-rail

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It is shown that, on average, high-speed railway systems usually consume 29% less energy than conventional railway systems. With a comparison of the levels of energy consumption and emissions of high-speed passenger trains with those of all other modes of transportation with which it competes (including conventional passenger trains), the net effects on emissions of high-speed train service on any corridor in the study can be analyzed. This is important because even if the difference in the energy consumption of the Spanish high-speed rail system, Alta Velocidad Española (AVE), and that of conventional rail system is not significant or even if AVE consumes more energy, the diversion of passengers from air travel ultimately yields significant reductions in energy consumption and emissions on a route. The study concludes that each high-speed train passenger accounts for an emissions reduction of approximately 30 kg of CO2 and that this reduction increased on the routes on which AVE reaches higher speeds.

Energy Consumption and Emissions of High-Speed Trains - Alberto García Álvarez, 2010

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Energy consumption relative to the Duplex train should also be reduced by 20%, a result expected by lightening the weight of the train, improving aerodynamics and installing more efficient traction equipment.

https://rollingstockworld.com/passenger-cars/alstom-unveiled-the-first-passenger-car-of-the-avelia-horizon-high-speed-train/

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Energy Consumption Analysis of High-Speed Trains under Real Vehicle Test Conditions

Qing Zhang, Hongjun Yu, Xin Su, Yao Li