3 ms·

It's an exaggeration. But aeroplanes have gotten much, much more efficient (and quieter) --- this suggests an improvement of 55% since 1950: https://en.wikipedi

It's an exaggeration. But aeroplanes have gotten much, much more efficient (and quieter) --- this suggests an improvement of 55% since 1950: https://en.wikipedia.org/wiki/Fuel_economy_in_aircraft https://en.wikipedia.org/wiki/Fuel_economy_in_aircraft Looking at actual figures: Concorde got about 5MJ per passenger-km. A modern 747-400 gets about 0.9MJ per passenger-km. Meanwhile trains vary enormously but US trains appear to get about 2.7MJ per passenger-km, while Portugese ones are about 0.07MJ; but I don't know if that's comparing like with like (the data is unclear). Cars seem to get about 1.2MJ per passenger-km. A big cruise ship seems to get about 5.9MJ per passenger-km, plus you need to spend lots more energy on, essentially, life support because they're so slow. These numbers were brought to you by https://en.wikipedia.org/wiki/Energy_efficiency_in_transportation https://en.wikipedia.org/wiki/Energy_efficiency_in_transport... and the 'units' command, which is awesome. Also, someone who isn't me needs to overhaul that page to use consistent units everywhere.

CydeWeys 10y ago
> US trains appear to get about 2.7MJ per passenger-km, while Portugese ones are about 0.07MJ I'm with you, there has to be some flaw with differing methodologies going on here. It's way too discordant. I'm surprised at the 2.7 figure; are trains really more than twice as worse as individual passenger vehicles? I can't imagine so. Especially not the trains I use most often, electric-powered urban subways.
- vonmoltke 10y ago
  I'm on my phone right now so I can't post nice details, but the Wikipedia number for "Portugal" is mislabeled. Per the reference, that is just for the Lisbon rail system. The US DOE report the US number was sourced from averages all passenger rail systems in the US, and specifically notes significant system-to-system variance. The biggest variance is that the Lisbon numbers are based on an average of about 400 passengers per train kilometer, while the US averages only about 40 across all systems.
- david-given 10y ago
  Yeah, that seemed really odd to me, but I thought maybe it was due to diesel vs electric-with-regenerative-braking, which can be disturbingly efficient. Trains should be vastly more efficient than any individual transport. The only US commuter train I've seen was the SFO Caltrain, which was very not electric. Are there many electric trains there?
  - ghaff 10y ago
    >Are there many electric trains there? Yes. For example, Amtrak's Northeast Corridor is electric as is light rail for the most part (entirely?). There's also an electrification project underway for Caltrain. I'm not sure about how much commuter rail in the US is electric in general.
- Someone 10y ago
  The higher the speed, the more important avoiding air resistance is to get high efficiency. Planes are efficient, ones they are high up in the sky because there is less air there. Unfortunately, they need lots of energy to get up in the low pressure regions, and we do not have ways to recover that energy in landing. Moving slower also increases the per mile efficiency, as air resistance grows faster than linear in speed. Net effect (highly simplified) is that trains beat high speed trains irrespective of distance, high speed trains beat planes on shorter distances (up to a few hundred miles), but planes beat high speed trains if the distance covered in one hop is large enough. Hyperloop aims to change that by being a train riding at low atmospheric pressure (planes don't only burn fuel to go from A to B, they also burn fuel to stay up; hyperloop wouldn't need to do the latter) (edit: ideally, it also would recover energy on braking)
bigiain 10y ago
So that's half an order of magnitude in 70 years - which feels much more "Yeah, I can believe that". (Not that trusting gut-feel is a great way to do science or find truth, but checking facts when your gut feel says "Nope" is always a good idea...) Also, that's a little bit of an apple to oranges comparison - I wonder what the numbers look like comparing a Concorde-vintage 1976 (or 1969?) 747 with a modern 747? Or even an A380 (Which I guess is the nearest modern counterpart of a mid '70s 747?)

CydeWeys 10y ago

> US trains appear to get about 2.7MJ per passenger-km, while Portugese ones are about 0.07MJ I'm with you, there has to be some flaw with differing methodologies going on here. It's way too discordant. I'm surprised at the 2.7 figure; are trains really more than twice as worse as individual passenger vehicles? I can't imagine so. Especially not the trains I use most often, electric-powered urban subways.

vonmoltke 10y ago
I'm on my phone right now so I can't post nice details, but the Wikipedia number for "Portugal" is mislabeled. Per the reference, that is just for the Lisbon rail system. The US DOE report the US number was sourced from averages all passenger rail systems in the US, and specifically notes significant system-to-system variance. The biggest variance is that the Lisbon numbers are based on an average of about 400 passengers per train kilometer, while the US averages only about 40 across all systems.
david-given 10y ago
Yeah, that seemed really odd to me, but I thought maybe it was due to diesel vs electric-with-regenerative-braking, which can be disturbingly efficient. Trains should be vastly more efficient than any individual transport. The only US commuter train I've seen was the SFO Caltrain, which was very not electric. Are there many electric trains there?
- ghaff 10y ago
  >Are there many electric trains there? Yes. For example, Amtrak's Northeast Corridor is electric as is light rail for the most part (entirely?). There's also an electrification project underway for Caltrain. I'm not sure about how much commuter rail in the US is electric in general.
Someone 10y ago
The higher the speed, the more important avoiding air resistance is to get high efficiency. Planes are efficient, ones they are high up in the sky because there is less air there. Unfortunately, they need lots of energy to get up in the low pressure regions, and we do not have ways to recover that energy in landing. Moving slower also increases the per mile efficiency, as air resistance grows faster than linear in speed. Net effect (highly simplified) is that trains beat high speed trains irrespective of distance, high speed trains beat planes on shorter distances (up to a few hundred miles), but planes beat high speed trains if the distance covered in one hop is large enough. Hyperloop aims to change that by being a train riding at low atmospheric pressure (planes don't only burn fuel to go from A to B, they also burn fuel to stay up; hyperloop wouldn't need to do the latter) (edit: ideally, it also would recover energy on braking)

bigiain 10y ago

So that's half an order of magnitude in 70 years - which feels much more "Yeah, I can believe that". (Not that trusting gut-feel is a great way to do science or find truth, but checking facts when your gut feel says "Nope" is always a good idea...) Also, that's a little bit of an apple to oranges comparison - I wonder what the numbers look like comparing a Concorde-vintage 1976 (or 1969?) 747 with a modern 747? Or even an A380 (Which I guess is the nearest modern counterpart of a mid '70s 747?)