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The tunnel diameter is much smaller. Like 1890s-built London Underground diameter tunnels. The standard with US subway construction today is massive tunnels wi

The tunnel diameter is much smaller. Like 1890s-built London Underground diameter tunnels. The standard with US subway construction today is massive tunnels with huge, expensive stations. Seems to be a design choice from Musk.

danielbarla 8y ago
I think both of the latter approaches make sense in the context of their era. With classical train / subway-style approaches, it made sense to have a bigger upfront cost, so that you could have fewer (but larger) trains. On the other hand, with today's relatively reliable small-scale electric vehicles and automated driving, I can certainly see lots of smaller pods being perfectly viable. That said, I don't have any particular insight into the field itself; however I do have a respect for Musk's ability to rephrase the problem just slightly (e.g. landing boosters to save costs) and to turn the whole economics of the situation on its head.
- cyphunk 8y ago
  small pods introduce the insanity of the highway system into spaces meant for trains. perhaps there are some improvements to be made through automation and scheduling of lanes but it seems possible pods would prove to be significantly less efficient when compared to the traditional use of lanes with large vessels that hundreds of people fit into
  - danielbarla 8y ago
    I guess it depends on just what size vehicles we're talking about. I agree that having tiny one or few person pods would probably not be efficient. But a "10-person cars on rails", type of scenario might not be as insane as you make it sound. Since it neatly side-steps the most complex parts of automated driving, we could have the reality of a well orchestrated fleet of smaller units. These could link up for efficiency on demand (maybe even while in motion), then separate again if they are operating in a complex web. Having a cheaper way of making tunnels feeds back again into the loop. Without doing any rigorous analysis, I can't comment much, but I wouldn't dismiss it offhand.
    - ghaff 8y ago
      So, it would presumably be like loading small trams at a ski area--if they had lots of intermediate stops rather than maybe just one. Yes, those work. Everyone is typically also able-bodied enough to be skiing and you have attendants supervising the loading and unloading.
- rsynnott 8y ago
  > On the other hand, with today's relatively reliable small-scale electric vehicles and automated driving, I can certainly see lots of smaller pods being perfectly viable. How? These pods take 16 people, and per the article, only one can set off every 30 seconds. This limits capacity to 2k people per hour (even assuming that it manages the promised numbers, and historically Musk stuff doesn't), which is far less than one would expect of a decent bus rapid transport line, never mind an underground train.
  - Lambdanaut 8y ago
    With a 10x increase in tunnel-boring speed, it may be possible to build several parallel tunnels, all serving the same route. In this case, each individual tunnel would be launching 16 people every 30 seconds. Parallelzation applied to subways.
    - jcranmer 8y ago
      Or, for 10% more cost, you could build a regular subway and move the same amount of people in much less space. You even reduce the truly expensive part of subways (i.e., stations), since you only have to have a mezzanine that covers two tracks rather than 20 tracks.
      - badwolf 8y ago
        Think about it from a redundancy standpoint. Single big trains get delayed due to any number of reasons - something on the tracks, broke-down train, etc... With 10 smaller tunnels, they can just be rerouted.
        jcranmer 8y ago
        Not really. If the other tunnels are essentially full up with other trains, then there's no space to squeeze in the trains from the blocked line. Furthermore, you'd have to have crossovers in place to enable that kind of routing, and those underground switching crossovers are not going to come cheap.
dullgiulio 8y ago
Usually you rate a boring machine by volume/hour so diameter is irrelevant. If Musk is ignoring that to say they are faster, it's snake-oil.
- spacenick88 8y ago
  But that really isn't the metric you actually care about. The only things that matter is distance tunneled per time and that the resulting tunnel can handle your transport needs. Musks believe is that the transport needs can be handled by smaller diameter tunnels than everyone else is boring. At least if they also built the "trains" and casually looking at subway networks that very well might be true.
  - WalterBright 8y ago
    A smaller tunnel can transport the same volume/time as a larger tunnel, if the transport is correspondingly faster.
    - masklinn 8y ago
      Why would it be? If you can run fast in a small tunnel you can run just as fast in a big one. The size of a tunnel is a factor of what you want to do with it and what you want to run through it. TBM manufacturers can scale down to 3ft if that's what you need.
      - WalterBright 8y ago
        > Why would it be? Building a new network would not be constrained by existing implementations. For example, you can't just drive the trains faster on existing systems. Everything would have to be redesigned/upgraded to do it - the motors, tracks, track bed, brakes, suspension, safety equipment, schedules, signals, everything.
        masklinn 8y ago
        > Building a new network would not be constrained by existing implementations. That doesn't answer the question. Why would the transport be "correspondingly faster" in a smaller tunnel than a bigger one, given both are new digs?
lorenzobr 8y ago
It's definitely a design choice. Generally, every city has big transportation hubs - airports, train stations and so on - located at strategic places within the city. Musk's idea is to ditch these hubs and replace them with more frequent and much smaller stations which get you closer to your destination. On the other side if they don't have to move millions of people to the same hub but rather move a much smaller number of people, they can afford to dig smaller tunnels and stations which are way more easy and fast to build. For instance, in London every time they build a new transportation hub, it takes years. These stations are massive, they literally dig in every direction for several meters. I don't know if it's going to work but surely there's thinking behind it. Edit: typo
- phil21 8y ago
  I think if this tech proves to somehow work (aka actually reduce expenses by at least 10x) the real play becomes PtP tunnels that don't follow the traditional "heavy rail" subway routes, but connect to those stations for transfer. This also could really only be the long time play anyways - it's the only reason using autonomous battery powered model X's as the "cars" makes much sense. I think it's an interesting idea, Musk obviously likes his sci-fi. He is basically attempting to implement packet switching for human mass transport vs. the current circuit switching we have.
- jcranmer 8y ago
  > On the other side if they don't have to move millions of people to the same hub but rather move a much smaller number of people, they can afford to dig smaller tunnels and stations which are way more easy and fast to build. The actual cost of tunneling itself is generally fairly cheap--somewhere around $50 million / mile. The expensive part is the stations. You can probably save money without having to build mezzanines, but the lower utilization of the tunnel and the greater number of vertical access shafts needed (not to mention the challenges inherent in moving through that very crowded portion of real estate) is probably going to cause cost blowouts compared to subways. Particularly if you design the tunnels to move cars, not people (SOV cars being about the worst use of space possible).

danielbarla 8y ago

I think both of the latter approaches make sense in the context of their era. With classical train / subway-style approaches, it made sense to have a bigger upfront cost, so that you could have fewer (but larger) trains. On the other hand, with today's relatively reliable small-scale electric vehicles and automated driving, I can certainly see lots of smaller pods being perfectly viable. That said, I don't have any particular insight into the field itself; however I do have a respect for Musk's ability to rephrase the problem just slightly (e.g. landing boosters to save costs) and to turn the whole economics of the situation on its head.

cyphunk 8y ago
small pods introduce the insanity of the highway system into spaces meant for trains. perhaps there are some improvements to be made through automation and scheduling of lanes but it seems possible pods would prove to be significantly less efficient when compared to the traditional use of lanes with large vessels that hundreds of people fit into
- danielbarla 8y ago
  I guess it depends on just what size vehicles we're talking about. I agree that having tiny one or few person pods would probably not be efficient. But a "10-person cars on rails", type of scenario might not be as insane as you make it sound. Since it neatly side-steps the most complex parts of automated driving, we could have the reality of a well orchestrated fleet of smaller units. These could link up for efficiency on demand (maybe even while in motion), then separate again if they are operating in a complex web. Having a cheaper way of making tunnels feeds back again into the loop. Without doing any rigorous analysis, I can't comment much, but I wouldn't dismiss it offhand.
  - ghaff 8y ago
    So, it would presumably be like loading small trams at a ski area--if they had lots of intermediate stops rather than maybe just one. Yes, those work. Everyone is typically also able-bodied enough to be skiing and you have attendants supervising the loading and unloading.
rsynnott 8y ago
> On the other hand, with today's relatively reliable small-scale electric vehicles and automated driving, I can certainly see lots of smaller pods being perfectly viable. How? These pods take 16 people, and per the article, only one can set off every 30 seconds. This limits capacity to 2k people per hour (even assuming that it manages the promised numbers, and historically Musk stuff doesn't), which is far less than one would expect of a decent bus rapid transport line, never mind an underground train.
- Lambdanaut 8y ago
  With a 10x increase in tunnel-boring speed, it may be possible to build several parallel tunnels, all serving the same route. In this case, each individual tunnel would be launching 16 people every 30 seconds. Parallelzation applied to subways.
  - jcranmer 8y ago
    Or, for 10% more cost, you could build a regular subway and move the same amount of people in much less space. You even reduce the truly expensive part of subways (i.e., stations), since you only have to have a mezzanine that covers two tracks rather than 20 tracks.
    - badwolf 8y ago
      Think about it from a redundancy standpoint. Single big trains get delayed due to any number of reasons - something on the tracks, broke-down train, etc... With 10 smaller tunnels, they can just be rerouted.
      - jcranmer 8y ago
        Not really. If the other tunnels are essentially full up with other trains, then there's no space to squeeze in the trains from the blocked line. Furthermore, you'd have to have crossovers in place to enable that kind of routing, and those underground switching crossovers are not going to come cheap.

dullgiulio 8y ago

Usually you rate a boring machine by volume/hour so diameter is irrelevant. If Musk is ignoring that to say they are faster, it's snake-oil.

spacenick88 8y ago
But that really isn't the metric you actually care about. The only things that matter is distance tunneled per time and that the resulting tunnel can handle your transport needs. Musks believe is that the transport needs can be handled by smaller diameter tunnels than everyone else is boring. At least if they also built the "trains" and casually looking at subway networks that very well might be true.
- WalterBright 8y ago
  A smaller tunnel can transport the same volume/time as a larger tunnel, if the transport is correspondingly faster.
  - masklinn 8y ago
    Why would it be? If you can run fast in a small tunnel you can run just as fast in a big one. The size of a tunnel is a factor of what you want to do with it and what you want to run through it. TBM manufacturers can scale down to 3ft if that's what you need.
    - WalterBright 8y ago
      > Why would it be? Building a new network would not be constrained by existing implementations. For example, you can't just drive the trains faster on existing systems. Everything would have to be redesigned/upgraded to do it - the motors, tracks, track bed, brakes, suspension, safety equipment, schedules, signals, everything.
      - masklinn 8y ago
        > Building a new network would not be constrained by existing implementations. That doesn't answer the question. Why would the transport be "correspondingly faster" in a smaller tunnel than a bigger one, given both are new digs?

lorenzobr 8y ago

It's definitely a design choice. Generally, every city has big transportation hubs - airports, train stations and so on - located at strategic places within the city. Musk's idea is to ditch these hubs and replace them with more frequent and much smaller stations which get you closer to your destination. On the other side if they don't have to move millions of people to the same hub but rather move a much smaller number of people, they can afford to dig smaller tunnels and stations which are way more easy and fast to build. For instance, in London every time they build a new transportation hub, it takes years. These stations are massive, they literally dig in every direction for several meters. I don't know if it's going to work but surely there's thinking behind it. Edit: typo

phil21 8y ago
I think if this tech proves to somehow work (aka actually reduce expenses by at least 10x) the real play becomes PtP tunnels that don't follow the traditional "heavy rail" subway routes, but connect to those stations for transfer. This also could really only be the long time play anyways - it's the only reason using autonomous battery powered model X's as the "cars" makes much sense. I think it's an interesting idea, Musk obviously likes his sci-fi. He is basically attempting to implement packet switching for human mass transport vs. the current circuit switching we have.
jcranmer 8y ago
> On the other side if they don't have to move millions of people to the same hub but rather move a much smaller number of people, they can afford to dig smaller tunnels and stations which are way more easy and fast to build. The actual cost of tunneling itself is generally fairly cheap--somewhere around $50 million / mile. The expensive part is the stations. You can probably save money without having to build mezzanines, but the lower utilization of the tunnel and the greater number of vertical access shafts needed (not to mention the challenges inherent in moving through that very crowded portion of real estate) is probably going to cause cost blowouts compared to subways. Particularly if you design the tunnels to move cars, not people (SOV cars being about the worst use of space possible).