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> high-speed trains consume more energy than aircraft citation needed. It helps a lot that (electric) trains do not need to carry their own fuel. Also, trains

by titzer 6y ago

> high-speed trains consume more energy than aircraft citation needed. It helps a lot that (electric) trains do not need to carry their own fuel. Also, trains can run on low-carbon energy, whereas there is no viable alternative to jet fuel at the moment, and producing that from net-zero-carbon processes (akin to biodiesel) is not economical.

nickff 6y ago
Airliners travel in air that is >60% less dense than the air at sea level, and usually travel over or around energy-wasting terrain features and weather.
- titzer 6y ago
  That's not a citation, it's a random factoid, which doesn't make for a fruitful discussion. Other random factoids include: * trains are long * trains travel slower than airplanes, and drag is proportional to the square of speed * making conclusions solely based drag coefficients from the density of the air is sound reasoning One of these statements is false. I get that hackernews is just a forum for casual discussion of various technical topics, but overly categorical statements based on a reasoning in a vacuum (no pun in intended) just force the conversation into unproductive threads like this one. I'm kinda sorry I took the bait at this point.
  - deepnotderp 6y ago
    Trains are long, but skin friction drag is real. Traveling slower is a bug, not a feature. If you want to go slower, airplanes can be more efficient as well!
  - kerkeslager 6y ago
    > I get that hackernews is just a forum for casual discussion of various technical topics I hear this sentiment a lot, and I don't understand it. Trying to speak the truth isn't just optional outside formal contexts. There's no situation so casual that I it suddenly becomes appropriate to make up bullshit and present it as facts. That is to say, I agree with your larger point: if nickff wants to make the claim that trains consume more energy than aircraft, he'd better come up with a reasonable source for that information.
- newacct583 6y ago
  Yes, but they travel 5-10x faster than ground vehicles. Drag losses go linearly with air density and quadraticly with speed. Likewise the distance traveled is going to be higher on a rail network but probably in the "2x as far" realm. You're not going to make those two orders of magnitude up with this. I think if you want to make this analysis come out you need to include starting/stopping losses (and maybe fuel hauling, empty car overhead, etc...) to the train trip or somesuch. Naively trains are going to win and it's not even close.
saddlerustle 6y ago
Biodiesel is not economical and a dumb idea, but it's pretty cheap to make flying offset factory emissions like within the EU emissions trading scheme (works out to ~€3 per passenger-hour), or even direct air capture schemes (~$20 per passenger-hour). Zero marginal carbon flights still works out to be cheaper than most countries' high speed rail networks if you compare unsubsidised costs.
- titzer 6y ago
  Four things I would like to mention that don't come up generally in discussions like these: * Transportation infrastructure is a societal investment that produces benefits, it's not just about its cost. Investing in terrestrial transportation like trains, even if it is more expensive can give rise to proportionally greater societal benefits than air travel--think, a long-haul train has multiple stops, providing connection points for economic activity (smaller towns and cities connected through train stations) that planes clearly cannot. I actually think it's totally OK that trains require more investment because they may create larger network effects in the big picture. * In some sense, all societal spending is make-work. If we're going to have make-work programs, we might as well spend it on the best long-term strategy, which in my honest opinion, having lived in Europe for a number of years, is cities being well-connected with cheap and fast rail, subways, and trams. * Climate change is a real thing, and it's due mostly to CO2 emissions. It's gonna cost money to fix. We need to stop deploying the "but itz mah dollarzzzes" as an excuse not to act. We need to start thinking about paying back the absolutely massive debt we racked up from cheap and easy energy. * Carbon offsets are a shell game that we can play in the short run, but ultimate we need to get to zero carbon footprint, which cannot be accomplished with offsets alone. In summary, we better start paying up.
  - deepnotderp 6y ago
    High speed rail requires speeding up and slowing down too. And at 15m/mile it's significantly cheaper and better to build airports
    - mac01021 6y ago

by titzer 6y ago

nickff 6y ago

Airliners travel in air that is >60% less dense than the air at sea level, and usually travel over or around energy-wasting terrain features and weather.

titzer 6y ago
That's not a citation, it's a random factoid, which doesn't make for a fruitful discussion. Other random factoids include: * trains are long * trains travel slower than airplanes, and drag is proportional to the square of speed * making conclusions solely based drag coefficients from the density of the air is sound reasoning One of these statements is false. I get that hackernews is just a forum for casual discussion of various technical topics, but overly categorical statements based on a reasoning in a vacuum (no pun in intended) just force the conversation into unproductive threads like this one. I'm kinda sorry I took the bait at this point.
- deepnotderp 6y ago
  Trains are long, but skin friction drag is real. Traveling slower is a bug, not a feature. If you want to go slower, airplanes can be more efficient as well!
- kerkeslager 6y ago
  > I get that hackernews is just a forum for casual discussion of various technical topics I hear this sentiment a lot, and I don't understand it. Trying to speak the truth isn't just optional outside formal contexts. There's no situation so casual that I it suddenly becomes appropriate to make up bullshit and present it as facts. That is to say, I agree with your larger point: if nickff wants to make the claim that trains consume more energy than aircraft, he'd better come up with a reasonable source for that information.
newacct583 6y ago
Yes, but they travel 5-10x faster than ground vehicles. Drag losses go linearly with air density and quadraticly with speed. Likewise the distance traveled is going to be higher on a rail network but probably in the "2x as far" realm. You're not going to make those two orders of magnitude up with this. I think if you want to make this analysis come out you need to include starting/stopping losses (and maybe fuel hauling, empty car overhead, etc...) to the train trip or somesuch. Naively trains are going to win and it's not even close.

saddlerustle 6y ago

Biodiesel is not economical and a dumb idea, but it's pretty cheap to make flying offset factory emissions like within the EU emissions trading scheme (works out to ~€3 per passenger-hour), or even direct air capture schemes (~$20 per passenger-hour). Zero marginal carbon flights still works out to be cheaper than most countries' high speed rail networks if you compare unsubsidised costs.

titzer 6y ago
Four things I would like to mention that don't come up generally in discussions like these: * Transportation infrastructure is a societal investment that produces benefits, it's not just about its cost. Investing in terrestrial transportation like trains, even if it is more expensive can give rise to proportionally greater societal benefits than air travel--think, a long-haul train has multiple stops, providing connection points for economic activity (smaller towns and cities connected through train stations) that planes clearly cannot. I actually think it's totally OK that trains require more investment because they may create larger network effects in the big picture. * In some sense, all societal spending is make-work. If we're going to have make-work programs, we might as well spend it on the best long-term strategy, which in my honest opinion, having lived in Europe for a number of years, is cities being well-connected with cheap and fast rail, subways, and trams. * Climate change is a real thing, and it's due mostly to CO2 emissions. It's gonna cost money to fix. We need to stop deploying the "but itz mah dollarzzzes" as an excuse not to act. We need to start thinking about paying back the absolutely massive debt we racked up from cheap and easy energy. * Carbon offsets are a shell game that we can play in the short run, but ultimate we need to get to zero carbon footprint, which cannot be accomplished with offsets alone. In summary, we better start paying up.
- deepnotderp 6y ago
  High speed rail requires speeding up and slowing down too. And at 15m/mile it's significantly cheaper and better to build airports
  - mac01021 6y ago