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In the news or various other places, we see often that train travel produces significantly less greenhouse gas than air travel, without much information about how this is calculated. For example here : https://reporterre.net/L-avion-emet-1-500-fois-plus-de-CO2-que-le-train

On the other hand, they hardly ever mention if the infrastructure is taken in account. For train travel, stations, rolling material, rails, ballast, viaducts, tunnels, have to be built and maintained, sometimes replaced regularly. When passengers increase, new tracks and new stations have to be built, sometimes infrastructure extension can become very heavy. This is mostly done with construction vehicle running on diesel, and tons of concrete are used. The higher speed the train line, the more heavy is the infrastructure, in particular larger viaducts, longer tunnels, and rails used more quickly.

Air travel, as much polluting as it is, only needs airports and the planes themselves to be built and maintained. There's no need for infrastructure on the way between airports.

Maybe this is already taken in account in the calculation made "ready for the public" on the news, and that despite this the train is favourable. But I prefer to be always skeptical of the info and try to understand how this is calculated.

  • You still need infrastructure around the airport to get to it. Would you include this also? Also, air travel relies on radio and radar stations, which also need to be built & maintained. Furthermore, which type of train are we talking about? Electrical, diesel, coal? Which travel distance are you interested in? – Erik Oct 9 '19 at 7:30
  • @Erik Obviously all "gray energy" for infrastructure, including what you mentioned, would have to be calculated. I don't particularly care about one type of train or one particular travel distance, I just wish to know whether or not those "studies" are including infrastructure greenhouse emissions, which sounds to me massive especially in the case of high-speed trains. – Bregalad Oct 9 '19 at 16:01
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Cars, buses, trains, and planes: comparison including infrastructure

"Life-cycle Environmental Inventory of Passenger Transportation in the United States", a 2008 PhD dissertation, provides a comparison of various passenger vehicles, buses, commuter rail, and air travel. The results were summarized in an article in Environmental Research Letters, "Environmental assessment of passenger transportation should include infrastructure and supply chains".

The key comparison of all vehicle types is given in this figure (PKT stands for passenger kilometer traveled):

Energy consumption and GHG emissions per PKT by transport type

Factors included in the analysis

For each transportation mode, the following factors were considered:

  • Vehicle
    • Manufacturing
    • Operation
    • Maintenance
    • Insurance
  • Infrastructure
    • Construction
    • Lighting
    • Parking
  • Fuel production

The impact of infrastructure

From the figure above you can see that, as expected, infrastructure is a bigger factor for road and rail vehicles. To understand how much of an impact, the author includes a comparison to some other studies of passenger cars in the supplementary data, showing that considering infrastructure may increase the total lifetime energy usage by around 60%:

Study comparison of energy use in passenger car

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There is a 2016 report on the Carbon Footprint of Railway Infrastructure from the International Union of Railways [Union Internationale des Chemins de fer: UIC]. They express it in terms of a pay-back time: how long it takes to cancel out the emissions caused by construction through savings thought to come form reduced air and road transport. This begs the question, of course, as to whether you are actually diverting traffic from other modes or just promoting more traffic by providing more opportunities.

UIC assume the railways will induce 20% to 30% extra traffic, and the rest is diverted from road and air. On this basis, they arrive at payback times of 9 to 15 years.

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There are several current reports out that fossil-fuel emissions are continuing to increase even though natural-gas is replacing coal. Obviously, solar and wind is not making much difference either. So the trains are not going to be that great when the source of electricity is considered. But anything with zero-local emissions is often heralded. Well, the trains have overall efficiency rather than highest speed and that can be true even if they are not purely electric.

Now the airline industry is likely to target a carbon-neutral fuel usage. For instance, they can use ethanol developed from sorghum that is grown on non-irrigated land. Or they can use solar and wind power to make hydrogen from water and then combine the hydrogen with smoke-stack carbon-dioxide to make methanol.

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  • 2
    I don't think this answers the question, which was about infrastructure (airports, rails, stations, etc) – aucuparia Dec 18 '19 at 9:16
  • Trains have a known efficiency of economy. Aircraft have a known efficiency of time. They each already relate to their required infrastructure. Aircraft systems can't match train systems on a per-pound carrying-capacity basis. – S Spring Dec 19 '19 at 5:00

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