

Musk's Hyperloop math doesn't add up - subsystem
http://greatergreaterwashington.org/post/19848/musks-hyperloop-math-doesnt-add-up/

======
zeteo
>The Hyperloop pods will travel[...] about 30 seconds apart in the tube. They
will have a maximum deceleration of 0.5 gs [...] it will take a pod 68.4
seconds to come to a full stop.

>That's a pretty significant issue because safe vehicle operation means never
getting closer to the vehicle ahead than the distance it will take you to
stop. [...] That means that the minimum separation between pods is probably
closer to 80 seconds or more.

Two flawed assumptions in here:

1\. 0.5 g is the maximum deceleration under normal conditions (see p. 58 in
Musk's PDF). Emergency braking would obviously be capable of more. The linear
accelerators themselves are spec'd to be capable of 1g, and there's an onboard
emergency braking system on top of that.

2\. A vehicle that crashes doesn't stop immediately, but continues on its
direction of motion due to inertia. That's why the two second rule is plenty
safe on highways [1], even though expected vehicle stopping times are six
seconds or more [2].

Furthermore, the article is basically an attack on maximum capacity, but
that's not a real issue. The system is economically viable if it can get
passengers from point A to point B at comfort and cost levels (including
recouping investment) that compare favorably with other means of
transportation; Musk cites $20 per ticket, which the article doesn't dispute
Maximum capacity can always be expanded if the economics work otherwise.

[1] [http://en.wikipedia.org/wiki/Two-
second_rule](http://en.wikipedia.org/wiki/Two-second_rule)

[2]
[http://www.csgnetwork.com/stopdistinfo.html](http://www.csgnetwork.com/stopdistinfo.html)

~~~
tptacek
Isn't that $20 estimate _prima facie_ incredible? It's based on the capex
costs of the system but not opex, right? It presumes that once you build the
system, it runs itself for free.

~~~
jfb
What I don't fully understand is how this is any better than conventional HSR.
What are the advantages? Cost, but that remains to be seen. Absolute speed,
which yes, but where are the time estimates from Hayward to the Transbay
Terminal in SF, and from Sylmar to Union Station in LA?

This whole thing reads to me as purest wind.

EDIT: At least on a conventional train, I can ride from somewhere that's not
at one of the endpoints to somewhere else that isn't; and, of course, I can go
to the bathroom.

~~~
pekk
> where are the time estimates from Hayward to the Transbay Terminal in SF,
> and from Sylmar to Union Station in LA?

How can they know where the track would run? You want an actual train schedule
already?

If it is unacceptable not to have a bathroom, then cars are also unacceptable.
Somehow it works for many people anyway.

I wonder whether existing HSR plans had to meet requirements this stringent.

~~~
jfb
Cars don't have bathrooms -- that is correct. However, cars _can take
unscheduled stops_ without triggering an emergency response.

And pitching this fluff as SF -> LA without tackling the last mile -- perhaps
the hardest part -- is all a reasonable person needs to know to know it's just
waffle.

------
RyanZAG
Aren't we arguing about the wrong things here? The hyperloop is actually
something worth having as it will get you from SF to LA in 30 mins. Even if it
costs more and takes less people than HSR, it's still far better than HSR for
actually getting you between the two cities in the kind of time people would
like. If you could set up these 30 min hops between cities all over the world,
you will _improve humanity as a whole_. That's something worth attempting.

If capacity becomes an issue, you could just add more tracks. If the cost is
wrong (and it no doubt is), why is nobody coming up with the real cost so we
can compare this properly? Hand waving about 'too low!' is only useful for
arguing, not for finding a solution. Are there other ways that the cost could
be brought down?

~~~
mistercow
>The hyperloop is actually something worth having as it will get you from SF
to LA in 30 mins. Even if it costs more and takes less people than HSR, it's
still far better than HSR for actually getting you between the two cities in
the kind of time people would like.

Not necessarily. It depends on demand.

Think of travel time as latency, and volume as bandwidth. If the system is
unsaturated, then the 30 minute travel time is great. You show up, get on, and
~30 minutes later you're at your destination.

But if the system is saturated (which seems likely at $20/ticket), then
latency becomes more or less irrelevant because you're limited by bandwidth.
Sure, once you get on the car, you'll arrive in half an hour. But you will
have to wait in line, and that wait will be determined by the volume
limitations of the hyperloop. If the hyperloop attempts to serve the same
demand as the proposed HSR, a passenger's total travel time will be four times
as long.

The solution is to charge more for a ticket. The actual price needs to be
calculated in terms of a point where you don't end up with more than 3000
passengers per hour (at which point you break even).

However, even if you do that, it doesn't as effectively solve other problems
that the HSR will help with, like total car traffic.

~~~
superuser2
Why would we create one of the most sophisticated transit systems in history
and then use _standing in a line_ as the method of reserving a space?

Web-based reservation systems are not hard. Last-minute tickets could be sold
at higher price for those that need and can afford them as well.

~~~
tptacek
You're not waiting in line for a ticket. You're waiting in line to get through
security and to board the capsule. This is one of SWA's core optimization
problems, and door-to-door times for SWA are still swamped by human-factor
airport issues.

You can't wave a web browser around as a magic wand to solve these problems.

~~~
superuser2
>and that wait will be determined by the volume limitations of the hyperloop

This is what led me to believe he was talking about standing in line for a
place in a capsule.

Why is the wait for security determined by the volume limitations of the
Hyperloop? Isn't that a function of demand, security lanes, and space to fill
with waiting passengers?

~~~
tptacek
Fly a lot? How much time do you give yourself to get through the lines?

~~~
superuser2
I print my boarding passes at home (or use Passbook) and never check luggage,
so the only line I deal with is security.

Passing through the checkpoint itself takes ~90 seconds. The other 20-90
minutes is waiting for the queue in front of me to be processed by 1-2 lanes
working in parallel. If the airport had a wide enough hallway and a big enough
payroll, why couldn't it run 10-20 lanes and cut down the wait by an order of
magnitude?

Obviously the federal government doesn't choose to spend money that way, but
it could - regardless of the seating capacity of the aircraft. In fact low-
bandwidth aircraft make the problem _easier_ because fewer people need to
depart at once.

I trust that you know what you're talking about when it comes to security, but
I don't see it. Why does Hyperloop's low bandwidth make the security line
problem worse than HSR?

~~~
tptacek
The HSR plan doesn't involve TSA-style security checkpoints. The Musk plan
explicitly does. HSR trains have derailed in the past with minimal fatalities.
The expectation is that the same scenario on Musk's trains would be
catastrophic.

------
anologwintermut
So his point about spacing may be true for loading and unloading, but it is
not for emergency stops. You can exceed .5g's in am emergency. With
appropriate restraints, 4 or 5g's would be possible.

The larger problem is: if you can build a hyper loop track at 10% of the cost,
you can build an ultra light conventional "train" on the same pylons and with
lighter weight,cheaper, track. It would run at maybe 200 or 250pm and hence
with reduced capacity. At best Musk's cost claims are a capacity/cost trade
off. At worst, they are suspect. I think they are suspect, especially given
the extreme tolerances of the tube

~~~
johntb86
I think one advantage of the hyperloop is that it would probably be quieter
(they claim the compressor uses <150 HP) so that would make putting it on a
pylon simpler and would reduce the need for noise barriers. Also the
separation between tubes could be much lower than the separation between
tracks. I'm not sure how much this would affect the feasibility of putting a
more normal HSR train on small, lightweight pylons, but it wouldn't help.

~~~
johntb86
Also, it has a large enough speed advantage that it doesn't have to go
straight to the city center to have a time advantage over air travel, and that
would be a big part of reducing the cost while keeping it viable.

------
jackfoxy
Comparing the theoretical capacity of the Hyperloop vs the High Speed Rail is
only one fact to consider. Musk correctly points out the High Speed Rail is in
theory way more dangerous. And, possibly more significantly, it is just too
slow. To expect travel consumers to opt to max-out the so-called High Speed
Rail capacity is wishful thinking. The real "high speed" capability of the
Hyperloop make it more likely consumers would opt to max out its capacity, at
which point more capacity can be added (by adding a parallel loop), and it is
still cheaper than the High Speed Rail.

------
Xcelerate
In the engineering field, I've found there's an issue with a subset of
engineers where they get some kind of enjoyment out of saying why something
_can 't_ be done without providing any suggestions or improvements to make it
possible. They just feel the need to be negative and list reasons why
something won't work. It's unfortunately common, it's unproductive, and it
really gets kind of annoying after a while.

~~~
tptacek
There's already an alternative plan on the table that does SF to LA, city
centers in both, in 2 hours 28 minutes.

To mount the argument that engineers and critics should be focusing on
rehabilitating Musk's proposal rather than shooting it down, one of the
following needs to be plausible:

(a) that door-door transit times on Musk's system will be significantly better
than the HSR plan

(b) that construction and operation of Musk's plan will be significantly
cheaper than HSR

(c) some X factor makes Musk's plan more attractive

There are compelling arguments against (a) and (b):

(a) because Musk's system can't reuse existing urban rights of way, it
terminates far from either city center. It gets a "~30 minute" estimate, which
message boards are eager to latch onto, by waving a magic wand and turning
Hayward into San Francisco and Sylmar into Downtown LA. If that was a viable
strategy, SWA would still be relying on Islip to service NYC.

(b) Musk's estimated tunneling and el track costs are so low that, were they
viable, they'd revolutionize all of the rest of urban planning. For instance,
Musk proposes to lower the cost of running viaduct by an entire order of
magnitude. No comparable tunnel has been built for anything like what Musk
proposes his tunneling costs will be. And the expenses he lays out make
optimistic assumptions about the routes he'll be able to use, especially
through the mountains.

It's gotta handily beat 2hrs 28min for the route people actually care about,
OR be substantially cheaper. These aren't nits: they're the entire motivation
for the proposal.

~~~
tedunangst
You must realize you're posting on "I could build that in a weekend" central.
When viewed through HN goggles, a train that goes 80% of the distance between
sf and la is identical to a train that connects downtown.

Facts, like tweets, have a size limit. "Hyperloop will connect areas
relatively near to sf and la" is too long. "Hyperloop will connect sf and la"
is a shorter, and therefore better, fact.

~~~
tptacek
It's true, but I love the threads that make me go look things up. I could
really give a rat's ass about the Hyperbloop, but what other than a Hyperbloop
thread could motivate me to go read up on the per-mile cost of mountain
tunneling, or the amount of traffic in Sylmar?

------
kevinpet
There may be some valid points in there, but I don't consider it very
productive to get this kind of info from this source. I'm not sure what their
agenda is, but it clearly doesn't have anything to do with economics or
transportation. From the authors recent articles, I have my doubts he would
approve of anything that isn't initiated by government. Consider this article
[http://greatergreaterwashington.org/post/19330/supreme-
court...](http://greatergreaterwashington.org/post/19330/supreme-court-limits-
communities-control-over-their-growth/)

Since I lack the expertise to know myself whether the numbers are plausible or
will work out, I need to rely on the expertise of others. And one of my ways
of evaluating the expertise of others is if they appear to be guided by facts
or by an agenda.

~~~
moocowduckquack
To be honest, it reads like a standard paid-for FUD piece.

~~~
ams6110
Both projects are impractical fantasies regardless.

~~~
moocowduckquack
Yeah, imagine high speed rail going down tubes. Next thing you know, they'll
be proposing to put one under the English Channel. Those crazy engineers.

------
austinz
Part of the problem is that HSR is fast, technically feasible, heavily used,
and economically viable in France, Germany, China, Japan, and other places.

So, the most useful analysis would be:

1\. What factors are preventing HSR from being fast, technically feasible,
heavily used, and economically viable in the United States? (More concretely,
why does California's HSR suck so much when it's been demonstrated that HSR
doesn't necessarily have to suck?) Demographics (e.g. population density and
layout)? Political and legal constraints? Terrain? Culture?

2\. How does the Hyperloop mitigate or sidestep these problems, due to its
superior specifications or design differences from HSR?

3\. For additional insight, what would California's HSR have had to do
differently to mitigate or bypass these issues, and would it even have been
possible?

~~~
ams6110
Americans prefer cars. It's that simple.

------
ackfoo
People have largely missed the salient points of Elon's proposal:

1) If America cannot understand the potential and purpose of innovative
technology, it is doomed to slide into socio-economic, scientific, and
technological poverty. The point is that building a slow and expensive HSR is
stupid, and people have approved it solely because they are, similarly, too
stupid to envision what is possible. The primary point of building the
Hyperloop is not to move people physically, but to move them intellectually.

2) the Hyperloop, as designed by Elon, has zero emissions. We should do it for
that reason alone, otherwise we are genuinely too stupid to exist, which fact
says more about us than any debate. If we do not begin building zero-emissions
systems, the debate will not matter because we will be gone.

3) Capacity problems are not an issue. Elon has intelligently anticipated a
diminishing requirement to physically move people because of the improvement
of telepresence technology. If you still need to travel as much as you did ten
years ago, you are an idiot. This trend will only increase. Elon is too savvy
to mention this explicitly, but he no doubt understands that the need to move
people physically is declining. The HSR will be mostly empty if it opens in
2024 with the capacity required in 2014.

4) Our entrenched institutions have failed us, not because of anything
specific that they have done wrong, but simply because they are entrenched. We
should build the Hyperloop for no other reason than a little revolution being
a good thing, now and again.

------
Aloisius
It seems some people don't quite understand what the big deal is about not
terminating outside the major population centers.

For people from the east coast, imagine a train system that claimed to connect
New York and DC, but actually terminated in Manville, NJ and Bowie, MD.

~~~
DanBC
Ryanair (budget European airline) does this.

EG: They fly you to Paris, not CDG or Orly, but to Paris Beauvais.

------
jdmitch
The most important issue in terms of long-term cost-effectiveness is how much
it will actually be used, and how much of the time it is actually full. High
Speed Rails or any trains for that matter, are plagued by the inefficiency of
having to run at a set schedule regardless of how many tickets are sold, and
they ultimately don't justify their own existence in most of America. The
hyperloop, aside from attracting new people who otherwise wouldn't have
considered rail travel, also has the benefit of having smaller capacity and
being able to adapt to demand more quickly. With no stops between SF and LA,
if there are no passengers at a certain time, you just don't send the vehicle
-its that simple.

~~~
devx
Or you _do_ send them, because it costs so little, and the hyperloop will be
mainly self-powered, instead of having them wait half an hour for others to
take the ride with them.

------
dojomouse
The capacity constraint accusation on the grounds of spacing and max G is
pretty bogus. Firstly, there's nothing wrong with running at far more than
0.5g in an emergency. You think a plane stays below 0.5g when it crash lands?
You just have to make sure people aren't badly injured, not pamper them - and
make sure such emergencies are very rare.

Where the author really gets it wrong though is in saying "Maybe he can
resolve that by using larger pods. But of course, a larger pod will weigh
more. And that will probably mean using stronger steel for the tubes, which
means that the cost will go up". That would be true, but if you're happy to
resolve the issue with larger pods then you should be equally happy to resolve
it with groups of smaller pods travelling at smaller separations. A 737-800
seats around 150 people. Hyperloop passenger capsules seat 30. So no one
should have any conceptual issue with running 5 hyperloop capsules in convoy
with separation of a couple of seconds. This 'couple of seconds' still means
almost 1km, so they're certainly not sharing the same segments of tube, so you
don't need to scale the tube design at all. It's still dirt cheap, and you
have plenty of capacity, and it's still MUCH safer than a plane because if one
capsule has a fault the others following can still likely stop in time (given
they're all decelerating at roughly the same speed).

------
Denzel
Isn't it incorrect to simply compare the capacity of the Hyperloop vs. the
High Speed Rail. Shouldn't the transport time also be taken into account?

I mean, simplifying of course, if the Hyperloop can carry ~3,000 from A to B
in 30 minutes, and the High Speed Rail can carry ~12,000 from A to B in 2
hours, which is better? In this scenario wouldn't they be equal?

~~~
anologwintermut
The measure is capacity per unit time. The hyperloop's capacity is much
smaller.

~~~
craftkiller
Well I'm from the east coast so I'm not the most familiar with SF/LA but how
many people per hour actually travel between those two cities? Would it really
exceed the 1,260? If not then the reduced travel time would certainly be a
huge benefit.

------
moocowduckquack
Even if he is right and the math does not add up, I do not think that Musk is
likely go to all this trouble to try and boost Tesla sales in California in
2026, which is the earliest that HSR is planned to get anywhere close to
connecting LA and San Francisco, and even then it actually only gets as far as
San Jose, the San Francisco bit is scheduled to open in 2029.

I can't see a plan involving the idea that in 2029 Tesla would be so dependent
on Californian sales rather than global, that it would seek to stop a local
rail network from progressing. Especially a plan so convoluted as to involve
actually taking time out from running a rocketship business, car company and
solar power company, in order to design a rail network that according to the
theory, you do not want built.

~~~
tptacek
He hasn't taken time away from his car company to do this.

~~~
moocowduckquack
He has taken time to do this, while being involved in running three other
concerns. This may not have taken time out of running any of those concerns
admittedly, perhaps he gave up reading for a bit, I don't know. But he must
have spent some time on it.

He says he was pulling all-nighters to get it ready for the press, and also
said _“I wish I had not mentioned it, I still have to run SpaceX and Tesla,
and it’s fucking hard.”_ , which seems to indicate that it was squeezing his
time.

Unless he has quite a lot of free time, which it doesn't sound like, I can't
see how this could have taken no time away from Tesla, especially given what
he has stated. It might not have taken that much, but it will have taken some.

~~~
tptacek
He had a white paper written. He didn't build a hyperloop. Let's make sure
we're talking about the same thing.

~~~
moocowduckquack
You know perfectly well that we are talking about the same thing. You directly
replied to a point that was talking about the effort involved in designing a
system, saying that he didn't take any time out from Telsa to do that.

All I am saying is that it seems likely that it must have taken some time out
from his other activities, especially if he is talking about pulling all
nighters just to work on the thing.

This seems so patently obvious that I am not entirely sure why you would even
contest the point, let alone then resort to rhetoric above sound argument to
try and win it.

~~~
tptacek
You wrote "a plan so convoluted as to involve actually taking time out from
running a rocketship business, car company and solar power company". I'm
pointing out that he took time out to write a paper; he hasn't taken time out
to build anything.

The question of his motives --- which is a sideshow --- would be easier to
dispense with if he had _actually invested in the proposal_.

~~~
moocowduckquack
You stripped the context of _" , in order to design a rail network"_ from that
quote.

He has to design the thing to then write a paper on the design. You are saying
that he took time out to do that as though it is not what I am saying, however
it is in complete agreement with what I stated in the first instance.

All I ever said was that he took time out to design the thing, and the paper
on the design is obviously the public part of designing the thing.

You keep coming up with this build nonsense, which I never implied at any
point and which you know is a non-point as anyone who has been following this
in the slightest, obviously knows that it hasn't been built yet.

And he has invested in the thing, he has invested the time it took to design
the thing to the level required to then write the published paper.

------
ck2
Plus since oil pipelines constantly leak, how are they going to make
pressurized tubes for miles that don't leak and trap pods?

