Train vs. Airplane Energy Efficiency (2010) | Hacker News Reader

Train vs. Airplane Energy Efficiency (2010)

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30 pointsTomte27 comments

These numbers are pretty different than the ones here:

https://en.wikipedia.org/wiki/Fuel_efficiency_in_transportat...

citation:

Davis, Stacy C.; Susan W. Diegel; Robert G. Boundy (2011). Transportation Energy Data Book: Edition 30. US Department of Energy. pp. Table 2.12. ORNL-6986 (Edition 30 of ORNL-5198). Retrieved 2012-02-22.

Passenger trains are more efficient than planes, even when low capacity is assumed.

What surprised me is how efficient air travel has become, it really is quite impressive.

The wikipedia page uses 2009 figures, versus 2005 from the article. Overall the wikipedia page is a more useful article.

I think a large source of the variability in those numbers is the (active travelers) per vehicle. It surprises me how carpooling is actually more effective than buses, but then I realize that it's a point transfer without a driver.

I wonder what automated route pooling and 'johnny cab' style self driving cars would do to those numbers?

Regenerative braking on trains seems like low-hanging fruit these days. Ah, yes, just did a bit of Googling and apparently it is standard equipment on most new trains:

http://www.climatetechwiki.org/technology/regenerative_braki...

Older, especially freight, trains where all power comes from locomotives still tend to lack regenerative braking though.

Neat. One thing that isn't addressed however is the sustainability of the energy source. Until we have electric airplanes, trains will continue to have a lower carbon footprint.

> One thing that isn't addressed however is the sustainability of the energy source.

You can make hydrocarbon fuel for airplanes if you have electrical power. There is no risk of running out, you can make it literally from thin air! All the atoms necessary are in air (although obviously there are easier sources).

On top of that we could save our oil for airplanes and use other fuels for land vehicles - doing that we'd have effectively unlimited amounts.

> Until we have electric airplanes, trains will continue to have a lower carbon footprint.

Being electrical does not automatically mean less CO2. I'm not following your logic.

Until we have electric airplanes

While I believe battery-powered cars like the Tesla S make more sense than hydrogen/fuel-cell based cars, perhaps fuel cells make sense in airplanes. For cars, the weight of batteries are an advantage as they provide down-force and can be readily charged by virtue of being close the ground where there's infrastructure, in stark contrast to flying at 36,000ft where infrastructure is non-existent.

Addendum: The infrastructure issues that come with fuel-cell distribution and refueling would be eliminated thanks to the centralized nature of airports.

I've seen a number of back of the napkin calculations involving electric airplanes, but even when compared with fuel cells, traditionally fuelled airplanes have the advantage that their weight greatly decreases as they use fuel. Apparently a significant portion of the range of an airplane comes from when the tanks have < 50% fuel. This shifts the economics even further in their favour, aside from simple energy density calculations (as you're lugging the now useless, yet still very heavy batteries / fuel cells all the way to the destination).

While I'd love to see a shift in a more sustainable direction, I wonder if we're going to be close to that anytime soon.

Good point, but we don't have commercial fuel-cell planes either. Swap "electric" with "clean fuel".

On the other hand weight is the enemy of everything good in cars.

Weight makes them worse , use more energy to move accelerate slower.

It isn't clear that electric is a lower carbon footprint, right? What if the electricity is generated at a coal plant?

Intuitively the train should be more efficient, right? So the question imo is why does the data say otherwise: Is there less market pressure to make efficient trains? Is this data wrong? Is this intuition wrong?

(edit to include questioning the intuition itself, i.e. based on the reply comment)

Everything else equal I agree, but everything else is not equal. The FRA says that all passenger trains have to be built crazy heavy duty in case of derailments. To the substantial detriment of fuel economy.

Thank you. I didn't know about that requirement; and it would obviously be ridiculous to stipulate that airframes be made heavy.

One reason for these tough requirements is that a very large portion of U.S. passenger rail routes go over track owned (and used) by freight rail companies. Therefore, passenger train collisions and other such risks are weighed not only against other passenger trains, but also heavier freight trains.

This is one reason why U.S. trains have (relatively) 'harsher' requirements than other countries where track is not shared to such a high extent.

Separately, this degree of track-sharing is one of the reasons why average passenger rail journey speed has decreased in many places over a 100-year time period!

Obviously, in both cases, there are many many factors involved - but, an important element.

Planes are made heavy, for the same reasons as trains: safety enhancement and cost reduction.

Ever notice how every wheelie cart on a plane has not one but two locking handles to secure it? How about the ram air turbine [1] which is used almost never but weighs hundreds of pounds? Seat frames are still made mostly of metal, whereas if weight were the only consideration they would probably be carbon fiber.

[1] https://en.wikipedia.org/wiki/Ram_air_turbine

Yes, I would not dispute your statement, but that does not contradict the fact that airframe weight is minimized to increase efficiency. I did notice the seats were mostly metal, but I also noticed their (essentially) honeycombed design: they are mostly the rigid frame, rather than solid metal. I'm sure if they could reasonably remove the ram air turbine, they absolutely would (both for cost and efficiency).

It's the same pitfall that Hydrogen powered vehicles. Yeah they clean, but everybody forgot form where we get the hidrogen. You need to use electric energy to get it from water or get it from hydrocarbon fuels.

How ever, moving all to electric powered, at least allow us to replace a single thing (electric generation stations) to something more clean, like a mix of solar/wind/geo/hydro power sources + nuclear)

Obviously electricity doesn't necessarily come from a clean source, but it at least has the potential to.

We have electric planes. How ever we have a problem of energy storage/generation density that actually make unviable beyond drones and experimental planes that don't carry cargo.

Two things that are out of scope for this article: Emission altitude may change how certain emissions affect the environment and specifically the climate: "Emissions weighting factor (EWFs) i.e., the factor by which aviation CO2 emissions should be multiplied to get the CO2-equivalent emissions for annual fleet average conditions is in the range 1.3–2.9."[0]

The other thing is that apart from the emissions per mile, you tend to travel more miles when you use a plane -- a magnitude more. Regardless of whether you take a car, a train or a plane, motorized mobility is only sustainable up to a point, and planes make it very easy to go (fly) beyond that point.

[0] https://en.wikipedia.org/wiki/Energy_efficiency_in_transport...

I seem to remember reading that plane travel is inherently more disastrous to the planet, because of where planes fly - the pollutants are deposited 30,000 feet in the air, rather than near ground level. I seem to have not found a reference for this though.

This is what I am referring to (sorry to have used such layman's terms, I am in fact: not a scientist) :

https://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch2s2-2...

Interesting article. I too assumed trains to be much efficient than airplanes.

The big difference between rail and air is that it is possible to have a functioning market economy with true competition between airlines whereas rail seems to be stuck with bureaucratic monopolies.

That causes air travel to get cheaper and cheaper, better and better while the train travel just falls more and more behind.

It doesn't mention one of the main advantages of planes: air resistance is much lower at 40,000ft (although that is obviously offset by increased speed of jets compared to trains, which results in increased resistance).

Another factor is the energy cost of building & maintaining the infrastructure. Aiports, ATC, etc. vs stations, tracks, etc.

  Thus one may say that passenger trains are potentially 
  energy efficient, but in actual practice such trains turn 
  out to be little more energy-efficient than the airplane. 
  What institution changes are needed to realize the 
  potential of rail's inherent energy-efficiency are not 
  clear.

Three things:

  1. Render the skill set necessary for piloting any 
     aircraft down to a level of ease as trivial as 
     operating any train. This is not to say that operating
     a train is trivial. Nor that such a feat of 
     equivocation is even possible.

  2. Reduce the failure mode of every aircraft to failure
     modes on par with those of stalled trains, such that 
     a stalled aircraft merely risks mid-air collisions
     with other aircraft still in motion, with outcomes 
     similar to those of a moving train colliding with a 
     stalled train, stuck on the same track. This includes
     accounting for the level of inconvenience and options 
     available for re-routing and remediation of stalled 
     passenger flights, stranded in mid-air, as if they were
     trains stalled on a track. 

  3. Provide insurance coverage that promises that should
     the two preceding requirements not be met, when an air
     disaster does eventually occur, financial costs are 
     reduced to costs comparable to scenarios under which 
     a train might have suffered a similar scale of 
     disaster. Consider the Lac-Mégantic rail disaster [1], 
     for industrial incidents, consider passenger train 
     derailments occurring on bridges [2] for incidents 
     involving passenger fatalities. Obviously financial 
     compensation cannot redress the loss of human lives, 
     but only serve to bankrupt negligent operations that 
     fail to properly protect the lives of the passengers 
     and bystanders that entrust their territories and 
     well-being to said services.

[1] https://en.wikipedia.org/wiki/Lac-Mégantic_rail_disaster

[2] https://en.wikipedia.org/wiki/Tangiwai_disaster

Based on this, I would assume that a natural equilibrium in human motivation to take on roles either in rail transportation or air transportation would attract a similar or even interchangeable class of personnel, and thus provide similar capacities of efficiency to both sectors of the transportation industry, based on the relative equivalence in the quality of the staff occupying similar positions in each type of service.

Working on railroads is not as sexy as working in airplanes, both in terms of the perception of danger, as well as perception of implicit social status. Level the playing field between the task of operating railways with that of flying airplanes, and maybe people will be just as motivated to deliver super-efficient rail travel, as they are to deliver world-class airline service.

Air travel has become pretty prosaic now.

I'm in Taiwan at the moment, and there is something pretty pleasing about travelling on the HSR rail here - it seems more in line with the bullet trains of Japan, than the fast trains in Europe (which are still good - discounting the UK, which just has the Eurostar).

The trains all go extremely fast on mostly dedicated lines and the stations are the larger modern type - reminiscent of airports, but without the mega long walks or security.

Google image search -

https://www.google.com.tw/search?q=high+speed+rail+taiwan&so...

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