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I'd been trying to stay out of this pie fight.  But there's so much that's being said about hyperloop that's just so.... well, as XKCD says:

And this diary pushed me over the edge.  I mulled over writing the response as a comment, but I came to the conclusion that I'd probably get asked to make it a diary anyway, and the diarist in question is hardly the only person making these claims.  So a diary it is.

So let's begin, with  focus on the claims therein.

First off, of course, one can't begin any proper debate without questioning someone's motives!

so when I first encountered the notion floated that this is just a car builder (well, an electric car builder) attacking a rival form of transport, I thought that might involve some shaky inference regarding motive for otherwise puzzling statements ...
Hey, he also runs a rocket company.  Maybe it's a plan to derail all travel on earth!  He owns a solar company - maybe it's just a plan to order more solar cells!

Or maybe, just maybe, a physics major who's on several national engineering boards and has made a career out of starting radical-concept high-tech engineering companies might actually have an opinion on the topic of high speed transit?  Dyathink?  Nah, always best to start off analyzing a tech proposal by attacking the author's motives!!

(Above: An physics/engineering geek proposed a radical high-tech concept?  He must be plotting evil!)

   ... This is worse than sideways acceleration: track standards for vertical acceleration are tighter than for horizontal acceleration, about 0.5-0.67 m/s^2, one tenth to one seventh what Musk wants to subject his passengers to. It’s not transportation; it’s a barf ride.
First off, hyperloop never accelerates at 0.67.  It tops out at 0.5, as per the proposal.  The 0.5g is forwards and reverse acceleration in the accelerator segments.   And "a barf ride"?  Does the author realize normal G forces from commercial airplane takeoff and landing can reach 1g (plus gravity), with it not being considered a "hard landing" until you exceed 2g?

Lastly, there would be zero lateral acceleration in hyperloop because pretty much by definition the air cushions would float the capsules to be oriented vertically to the net force of acceleration.  On a near-frictionless system with no rails, acceleration can only be fowards, backwards, and downward, never lateral - there's nothing holding it at a particular angle to the ground.

Amusingly enough, the California HSR budget for the Central Valley is under $10 billion. Ie, in the same ball-park as this proposal.
In the words of Wikipedia, "Citation needed".  I've seen news articles on specific towns in the central valley which had cost overruns in the order of 3 billion.  

The CAHSR figures are very easy to distort about because of how they're categorized.  For example, I had one person arguing that land acquisition is cheap, only 4% of the total.  Yeah, if you just count the raw purchase price of the land the rail goes on . But that doesn't include legal fees for lawsuits, environmental studies, infrastructure improvements, and all of the rest, which brings it up to a large chunk of the total cost but which are slotted into other categories.  

(Above: HSR requires a sizeable amount of land acquisition on each side of the track.  How many such signs do you think you'd see for a structure built only on pylons every 100 feet, the majority of which are in the median of I-5?)

where you have years of property acquisition. In the shorter term, the plan for HSR is to simply share existing tracks, which the Hyperloop can't do.
Which is ridiculous; it can go over them.  The whole point of elevating hyperloop is to let it go over things - why toss away that primary design principle in town?  Making it no harder to get in-town, if so desired, than to travel out of town.  And if you'll check a map, you'll see there's a nice straight track straight from Sylmar all the way downtown.  There's one moderate curve in SF to get onto a track, but from there you can go straight to the Bay Bridge.

As Musk stated, Hyperloop was a cross between an airline and a high speed train.  The initial plan indeed seems like a cross between the two - three times the capacity of the SF/LA air link but 1/4th that of an idealized HSR, with "stations" on the outskirts like airports - but with faster throughput and dramatically lower ticket prices and nearly no per-ride environmental footprint.  Expanded plans are included in the design for reaching more destinations and capacity.

Security-wise, it’s easy to destroy this system by making a small dent in the tube. Yes, it’s one inch thick steel, but there are easily attainable ways to dent one-inch steel.  When you hit a small bump protruding inside the tube while going at Mach 0.9, nothing good can possibly happen regardless of capsule suspension design. As proposed the system is impossible to secure.
Then HSR is doubly difficult to secure, since it's just as sensitive to bumps, yet it's on the ground, not dozens of meters up.  HSR is so sensitive to bumps (wheels don't work well to begin with at those speeds) that the track can't even include expansion joints.  One of the main reasons that HSR track is so expensive is that it has to be continuously welded - but more than that, the rails must be heated first and welded hot, and then anchored very heavily into the ground, so that the track is in a constant state of tension.  Otherwise, the trivial changes from thermal expansion would cause that tiny bit of buckling that would derail HSR (Hyperloop deals with thermal expansion with automatically adjustable 3-axis dampers plus some extra tube at both ends to feed in or out).

Did I mention that on the ground an earthquake can sheer right through your track?

(Above: High speed rail is already engineered to very tight tolerances and can no more tolerate bumps or deviations than Hyperloop)

... and passenger capacity, based on egregiously unrealistic headways:
Can you imagine how sparse a highway would look like if each vehicle was 30 seconds from the one in front of them?  And "seconds" is a metric that takes into account speed - if you want a purely distance metric, 30 seconds at 750mph is 4.2 miles apart.  Airplanes fly at similar speeds with 3 mile horizontal separation when within radar range, and they have human operators and have to deal with turbulence.
There will always be the risk of equipment failure or tube damage that will cause a sudden and unplanned stop,
In a magical world where inertia ceases to exist.  Even if for some reason the vehicle ahead of you completely disentigrated, it's still moving at nearly mach 1.  A vehicle cannot simply just stop, no matter what happens to it.  It doesn't even have much air resistance to slow it down in the tube.  
the time for the preceding capsule to clear a junction and free the routing through the junction to be changed for the following capsule... (etc)
No, the tube simply shuts down, existing vehicles go to their destinations if in front of the problem, other vehicles stop and go to the nearest emergency exit.  As described in the document.
This is no different than for HSR, and the resulting minimum headways are usually several times longer than the emergency braking distance.
First off, HSR is human-controlled, which demands greater reaction times.  Secondly, HSR has to in places share tracks with other trains and to travel through urban areas, which is going to inherently increase the separation times.  Automated systems have no trouble with 30-second reaction times - plenty of roller coasters launch cars 30 seconds apart.  If a problem is detected, the system responds automatically.  Hundreds of millions of people every year trust their lives to such systems with similar time-separations to hyperloop, and fatal accidents are rare.  Certainly far rarer per mile than automobiles.  And speaking of automobiles, anyone remember the standard separation that students are tought to not go less than on the highway?  Two seconds.  With a human behind the wheel!

(Again, to reiterate: putting separations in seconds is a speed-independent metric.)

But as Greater Greater Washington points out, when the egregiously unrealistic headways are modified to merely optimistic headways, the capacity of the system falls away:     That means that the minimum separation between pods is probably closer to 80 seconds or more. Not a big deal. It still means 45 departures per hour. But that's only 1,260 passengers per hour in capacity. That's 10% of what the California High-Speed Rail can carry.
And if we make up numbers for HSR that are not in line with what's actually proposed, why we can give it less capacity than a rowboat!
When we adjust for the promised capacity, we would have to build four to five systems to match the maximum HSR system capacity, so the headline "$6b cost" is not really a 90% discount: its actually a 40% to 60% cost discount.
If one completely discounts what's actually proposed.  The tube cost is only $650 million of the total cost (if you run the numbers on the steel, you'll find out that that's a more than generous figure - I ran them myself).  Extra tubes may mean at worst reinforcing the pylons.  It certainly doesn't mean more land acquisition and the battles over that - the biggest portion of the costs.
The unit costs for viaducts on California HSR, without overhead and management fees, are already several times as high as Musk’s cost: as per PDF-page 15 of the cost overrun breakdown, unit costs for viaducts range from $50 million to $80 million per mile.
Except that Hyperloop isn't proposing rail viaducts.  The primary cost saving mechanisms of Hyperloop, as per the design, are:

1) The system is incredibly small and light (7-foot tube, entirely sealed, loaded vehicles 58 tonnes instead of thousands or tens of thousands)

1a) Small means "cheap to tunnel" (aka, 7 foot bore instead of 20+ foot bore)

1b) Light means "cheap to elevate"

2) The system is elevated:

2a) Elevated means you can build in the median and avoid land acquisition battles for the vast majority of the trip.

2b) It's hard to envision an easier environmental study to pass than a sealed, elevated structure in the middle of an area that's already been approved, bulldozed, levelled, and is daily exposed to tons of exhaust fumes.

2c) Elevated means far less space required per mile where land acquisition is necessary.
So pointing to high speed rail viaducts, designed to carry tens of thousands of tons, utterly misses the point.  Not to mention that as a general rule, they're built in the most difficult areas, meaning that by default they're going to be expensive.

(Above: Building 7-foot diameter elevated pipelines is not exactly rocket science.  Does this sort of elevated structure look even remotely comparable in cost to that of a rail viaduct?  The more weight you need something to bear, the more it costs, and trains are really, really heavy.  Hyperloop cars are not (and nor is 1" steel tube))

And of course the capacity of his proposed system drops if any appreciable share of passengers are overweight or have long stays on the other side, since he assumes 220lbs per passenger including luggage.
And airlines assume 180/185 pounds (summer/winter) plus an average of 25 pounds of checked bags per person.  The point?  Women and children do exist.

Another false criticism I've seen: one critical article pointed to the 27" seat width said that that's narrow compared to even airline coach seats.  Only the number they cited for coach seats was actually pitch (legroom).  Airline coach seats are typically 17-19" wide.  Seating in the hyperloop vehicles is, as described, quite luxurious.

Of course, Elon Musk is just putting this proposal out there: he is not going to be pursuing it himself.
Pardon the guy for having all of his financial resources tied up in moving the world off of oil and getting affordibly to outer space.  
The fact that Elon Musk was able to make a pile of money being the front-runner on getting substantial market share for an online payments system up doesn't make him any less of a dilettante when it comes to transport technology.
The author keeps bringing up PayPal, as though that's Musk's current business operation.  Musk hasn't been involved in PayPal for over a decade.  Musk's business ventures since then have been SpaceX and Tesla Motors.  And hey, let's take a moment to examine them, shall we?

SpaceX: Proposed the concept that a private company could get to orbit, payloads and people, at a tiny fraction the cost of the shuttle, and significantly cheaper than even the Russians and Chinese.  Moreover, he proposed doing this using two orders of magnitude less money than NASA was spending to develop their new, "cheap" rocket.  He was widely derrided in a bunch of articles like the one I'm critiquing here.  Result?  NASA's Ares rocket was a total failure, SpaceX's Falcon 9 is a big success, and now NASA is paying SpaceX for fourteen ISS resupply missions (as well as SpaceX serving private customers).

(Above: Mass-produced rockets cheaper than the Russians at two orders of magnitude less capital cost than NASA's failed rocket program?  Meh....)

Tesla Motors: Proposed not only starting up a new mass-production car company - something that in itself is almost impossible to achieve this day in age - but to do so producing electric cars, which at the time were sort of a laughing stock to the general population, and at a time that oil was far cheaper.  Furthermore, he proposed to get better than double the acceleration and range of the best serial EVs produced to date, and then to move on to making cheaper models with even greater range and at significantly lower prices.  He was widely derrided in a bunch of articles like the one I'm critiquing here.  Result?  Tesla has now produced and sold over 20,000 Model S cars, which have received some of the best vehicle reviews ever and great customer satisfaction ratings, and is showing no signs of slowing.  

(Above: This plant makes electric cars, baby!  :)  )

But hey, it's much easier to make PayPal jokes, right?

By contrast, the Hyperloop only meets criteria 2. It is proposed to use an untested, yet to be developed technology,
Dear god, heaven forbid we develop gasp new technology!  Everyone, hide the womenfolk, someone's showed up in town with one of those new-fangled soul-stealing photocamera devices!

Isn't the whole utility of sentience to be able to advance technology to achieve greater things for the betterment of society?

and as proposed would never offer trip comfort that would attract a substantial share of passengers, so as proposed, it fails criteria 3 and 4.
Seating 50% wider than coach on an airline, more legroom, only 30 minutes inside, and with the most advanced infotainment systems out there... excuse me, what's the problem again?
   (#2) Los Angeles--Long Beach--Anaheim, CA, 12,150,996, HSR1, Hyperloop1 (just barely)
    (#13) San Francisco--Oakland, CA, 3,281,212, HSR1, Hyperloop1
    (#15) San Diego, CA, 2,956,746, HSR2, Hyperloop2
    (#28) Sacramento, CA, 1,723,634, HSR2, Hyperloop2
    (#63) Fresno, CA, 654,628, HSR1, Hyperloop2

Here are the ones directly served by the HSR system, but not the Hyperloop System:

    (#22) Riverside - San Bernandino, 1,932,666, HSR2
    (#29) San Jose, CA, 1,664,496, HSR1
    (#79) Bakersfield, CA, 523,994, HSR1
    (#87) Murrieta--Temecula--Menifee, CA, 441,546, HSR2
    (#102) Stockton, CA, 370,583, HSR2
    (#105) Modesto, CA, 358,172, HSR2
    (#112) Lancaster--Palmdale, CA, 341,219, HSR1

What It Says On The Tin: Hyperloop was described as being an intermediary between rail and airline travel.  It is not designed for short-distance hops (aka, LA to Riverside), nor long distance (aka, LA to NYC).  If you need a transfer, get a transfer.  You're going to need to transfer to something at the HSR station anyway unless you live across the street.

And hey, while we're at it - since we're in a mode to nitpick all of the little details about something that was just proposed for the first time mere days ago, care if we do the same thing for HSR?  Let's point out what the critics have to say.

Okay, first off, does one even need to mention the obvious punching bag, the price?  What's that, about $1500 per person, whether they plan to ever use it or not?  And of course we're talking about fares of $81 per person.  Of course both these numbers keep on rising, and I wouldn't be shocked to see them rise even further.  

The promised trip time is totally unrealistic.  The blended system proposal means sharing tracks with commuter trains and freight.  Anyone who's been on shared track (including myself) can tell you what that means.  Yeah, that Shinkansen to Yamagata was really chugging along until we had to weight forever for a freight train to clear.  190mph average with a top speed of 220mph?  In your dreams.  Real high speed uses dedicated lines.

For example, HSR proposes San Francisco to San Jose in 30 minutes, based on an assumed speed of 100-150mph.  While competing with three types of local trains and freight trains on just two tracks.  Sorry, but that's not even remotely plausible.  

In fact, that whole urban travel itself being criticized for hyperloop is one of the most unrealistic aspects of the proposed HSR speeds.  You simply can't go that fast in an urban area (in an unenclosed track, that is) without all kinds of problems.  Going 200mph through train stations?  Across railroad crossings, with pedestrians?  Unless you plan to rework all the existing track infrastrucure (which they don't), it's just not going to happen.  And yet they expect to get those speeds.  Gilroy to Bakersfield, 198 mph.  Including going through Fresno.  I mean, really?  

We were talking about frequency and capacity.  Track sharing would realistically drarmatically reduce how often HSR trains could launch.  Not only does this mean a huge capacity hit, but it also throws the revenue projections way off.  

Of course, the capacity issue may not even be relevant because their ridership estimations are pie-in-the-sky, with a way higher car-to-train conversion rate than can be seen in the real world (for example, Europe), which they achieve by artificially inflating what it costs to drive.  Combine that with, more realistically, slower travel times and higher fares, and... well, you can see where this is going.

Anyway, to loop back around to Hyperloop: no, the plan as proposed is not perfect.  Which is explicitly what was stated when it was proposed - suggestions from the public were invited.  But what it is is definitely worth consideration, and if not for CA, then for elsewhere: a super-fast, super-cheap, super-low-environmental-impact means of mass transit.  And contrary to the detractors, the concept is indeed something that could potentially deliver that, via a combination of lightweight, low-profile (aka, low-cost) connecting track and high launch rates of low-mass vehicles.

(And for the record, to preempt the attack-the-messenger: I'm not a rail opponent.  Quite to the contrary, I've travelled across the US on rail and spent three weeks travelling Japan on rail)

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