5 ms·

Can you elevate rail as easily? The short answer is, "yes." I've ridden on it. The slightly longer answer (as another commenter has pointed out) is that it dep

Can you elevate rail as easily? The short answer is, "yes." I've ridden on it. The slightly longer answer (as another commenter has pointed out) is that it depends on the weight of the train versus the weight of the hyperloop. I see no fundamental reason to assume that the hyperloop is lighter than the train. It could be so, but then, we could make smaller and lighter trains, too (light rail). Plus you don't get the same natural banking off the walls he talks about, which is relevant at these speeds. While rail could bank, you better be going at the right speed when doing so, too slow and you just fall laterally off the tracks. This is a problem even when you are at grade. The solution is known: tilt-trains. The track is banked such that the train will not fall over if it has to stop on the curve. The passenger cabin then tilts with respect to the wheels so that it always feels like the floor is "down" regardless of the speed that the train goes around the curve. The radius of curve sets the maximum speed the train can travel around it.

Turing_Machine 13y ago
"I see no fundamental reason to assume that the hyperloop is lighter than the train." Did you actually read the PDF? It doesn't carry its motor with it. That's a pretty big reason. Nor does it need the heavy-duty (and heavy!) trucks of a standard rail car.
- deleted 13y ago
  [deleted]
- jim-greer 13y ago
  A bigger factor is that the efficiency of a train depends on having all the cars connected to each other. With the hyperloop, the pods are spaced out, so there's no need for the structure to bear the load of a bunch of them at once.
- jessriedel 13y ago
  Turn down the nastiness. It's totally non-obvious that this isn't overshadowed by the weight of the tube. And it does carry a motor with it, just not one that's responsible for initial acceleration or for large air resistances.
  - Turing_Machine 13y ago
    Sorry if you perceived that as "nasty". The motor that it carries with it is about 146 horsepower. That's less than a Kawasaki Ninja street bike. The General Electric E60 locomotives currently in use on Amtrak crank out 6,250 hp (4,660 kW) and weigh 423,000 lb (192,000 kilograms). The weight of the tube doesn't really enter into it.
    - krschultz 13y ago
      The weight of a 10' diameter steel tube with 1" wall thickness is 125,000 lbf per 100 feet. Note that does not include the reinforcing braces, that is just the plate. The actual weight could be easily 2-4x greater. It also doesn't include the weight of the solar array. My bet is that it's not significantly different to compare a light rail (subway-like) system to a hyperloop in terms of weight.
      - Turing_Machine 13y ago
        The weight of the track ballast alone is more than that. Gravel is about 100 pounds per cubic foot, and you need about 12 cubic feet of ballast per foot of track, or 127,500 pounds. Then you get to add the rails and ties (or concrete sleepers), plus the vastly more heavy rolling stock. The reason I said that the weight of the tube doesn't enter into it is because the tube isn't moving. The only thing that matters in terms of energy use is the rolling stock.
        Anechoic 13y ago
        The weight of the track ballast alone is more than that. ? You don't need to use ballast & tie track on elevated structure, in fact it's rare to do so on modern rail structures.
    - jessriedel 13y ago
      Flippant comments like "Did you actually read the PDF?" are exactly the kind of needless small escalations that destroys the tenor of commentary at HN. Any time you write that, you could be writing "It's discussed on page XX". If the comment doesn't deserve a cordial response, then just downvote and move along.
apendleton 13y ago
You can't just make lighter trains; heavy rail is heavy because it has high capacity. These vehicles can be much lower-capacity per vehicle because the speed is very high, which means you get equivalent throughput even with much smaller per-vehicle capacity. It's just like how you can get the same amount of water through a high-pressure, low-diameter pipe as through a low-pressure, high-diameter pipe. So yes, you could make the rail lighter, but in order to match the proposed passenger throughput, it would have to go 700mph. Good luck with that.
- jessriedel 13y ago
  I would be very surprised if the numbers really work out the way you claim: that the weight for carrying a passanger is similar for trains and a tube, and that the weight advantage of a tube comes essentially from 3x speed allowing for a one third the linear density of passengers. Do you have a cite?
  - apendleton 13y ago
    No, this is just back-of-the envelope, admittedly. But the three factors that determine how many people you can move past a given point per unit of time are the frequency of the vehicles, the capacity of the vehicles, and the speed of the vehicles, so if you want to match the throughput of the proposed Hyperloop, but with rail traveling at 164mph, you have to either make the vehicles more frequent or higher-capacity, or both. I would expect rail to be much less frequent, at least if typical rail conventions are followed, meaning you'd need much higher-capacity vehicles, combined with the engines to bring them up to speed (which move along with the train). It doesn't take that much weight to get past what you could reasonably support on a pylon in a median... there's a reason inter-city rail isn't built this way.
    - mortehu 13y ago
      > the three factors that determine how many people you can move past a given point per unit of time are the frequency of the vehicles, the capacity of the vehicles, and the speed of the vehicles Why is speed relevant?
tlb 13y ago
The hyperloop passenger capsule is estimated at 15,000 kg, while a TGV weighs 400,000 kg. [1] https://en.wikipedia.org/wiki/TGV https://en.wikipedia.org/wiki/TGV Edit: I had the wrong numbers before, thanks to Shiffern for the correction.
- schiffern 13y ago
  The actual number for the hyperloop capsule is 15,000 - 26,000 kg. Still much less than the TGV, obviously.

Turing_Machine 13y ago

"I see no fundamental reason to assume that the hyperloop is lighter than the train." Did you actually read the PDF? It doesn't carry its motor with it. That's a pretty big reason. Nor does it need the heavy-duty (and heavy!) trucks of a standard rail car.

deleted 13y ago
[deleted]
jim-greer 13y ago
A bigger factor is that the efficiency of a train depends on having all the cars connected to each other. With the hyperloop, the pods are spaced out, so there's no need for the structure to bear the load of a bunch of them at once.
jessriedel 13y ago
Turn down the nastiness. It's totally non-obvious that this isn't overshadowed by the weight of the tube. And it does carry a motor with it, just not one that's responsible for initial acceleration or for large air resistances.
- Turing_Machine 13y ago
  Sorry if you perceived that as "nasty". The motor that it carries with it is about 146 horsepower. That's less than a Kawasaki Ninja street bike. The General Electric E60 locomotives currently in use on Amtrak crank out 6,250 hp (4,660 kW) and weigh 423,000 lb (192,000 kilograms). The weight of the tube doesn't really enter into it.
  - krschultz 13y ago
    The weight of a 10' diameter steel tube with 1" wall thickness is 125,000 lbf per 100 feet. Note that does not include the reinforcing braces, that is just the plate. The actual weight could be easily 2-4x greater. It also doesn't include the weight of the solar array. My bet is that it's not significantly different to compare a light rail (subway-like) system to a hyperloop in terms of weight.
    - Turing_Machine 13y ago
      The weight of the track ballast alone is more than that. Gravel is about 100 pounds per cubic foot, and you need about 12 cubic feet of ballast per foot of track, or 127,500 pounds. Then you get to add the rails and ties (or concrete sleepers), plus the vastly more heavy rolling stock. The reason I said that the weight of the tube doesn't enter into it is because the tube isn't moving. The only thing that matters in terms of energy use is the rolling stock.
      - Anechoic 13y ago
        The weight of the track ballast alone is more than that. ? You don't need to use ballast & tie track on elevated structure, in fact it's rare to do so on modern rail structures.
  - jessriedel 13y ago
    Flippant comments like "Did you actually read the PDF?" are exactly the kind of needless small escalations that destroys the tenor of commentary at HN. Any time you write that, you could be writing "It's discussed on page XX". If the comment doesn't deserve a cordial response, then just downvote and move along.

apendleton 13y ago

You can't just make lighter trains; heavy rail is heavy because it has high capacity. These vehicles can be much lower-capacity per vehicle because the speed is very high, which means you get equivalent throughput even with much smaller per-vehicle capacity. It's just like how you can get the same amount of water through a high-pressure, low-diameter pipe as through a low-pressure, high-diameter pipe. So yes, you could make the rail lighter, but in order to match the proposed passenger throughput, it would have to go 700mph. Good luck with that.

jessriedel 13y ago
I would be very surprised if the numbers really work out the way you claim: that the weight for carrying a passanger is similar for trains and a tube, and that the weight advantage of a tube comes essentially from 3x speed allowing for a one third the linear density of passengers. Do you have a cite?
- apendleton 13y ago
  No, this is just back-of-the envelope, admittedly. But the three factors that determine how many people you can move past a given point per unit of time are the frequency of the vehicles, the capacity of the vehicles, and the speed of the vehicles, so if you want to match the throughput of the proposed Hyperloop, but with rail traveling at 164mph, you have to either make the vehicles more frequent or higher-capacity, or both. I would expect rail to be much less frequent, at least if typical rail conventions are followed, meaning you'd need much higher-capacity vehicles, combined with the engines to bring them up to speed (which move along with the train). It doesn't take that much weight to get past what you could reasonably support on a pylon in a median... there's a reason inter-city rail isn't built this way.
  - mortehu 13y ago
    > the three factors that determine how many people you can move past a given point per unit of time are the frequency of the vehicles, the capacity of the vehicles, and the speed of the vehicles Why is speed relevant?

tlb 13y ago

The hyperloop passenger capsule is estimated at 15,000 kg, while a TGV weighs 400,000 kg. [1] https://en.wikipedia.org/wiki/TGV https://en.wikipedia.org/wiki/TGV Edit: I had the wrong numbers before, thanks to Shiffern for the correction.

schiffern 13y ago
The actual number for the hyperloop capsule is 15,000 - 26,000 kg. Still much less than the TGV, obviously.