Some details have finally been released by Elon Musk/SpaceX/Tesla Motors for the much-anticipated hyperloop system.
I have general red flag-type feelings when reading the pdf, but I will focus first on my my main general issue, and then talk about specific things that jumped out at me. I might expand on the general issue later as it’s something I always think about when reading about public transportation.
Jalopnik has an article today about it. The author shares some of the same reservations as me, which I will avoid overlapping with. Specifically:
the basic technology doesn’t sound that different from the vactrains he dismissed so blithely. In his paper, Musk says that the problem with the trains proposed by the RAND corporation in the 1970s was that they required too low of a vacuum to be reasonable. But go look at Salter’s 1978 RAND paper. In it, Salter says, “Cars travel in a reduced atmosphere of 0.1% of sea level pressure…” If that “0.1%” number sounds familiar, it’s because it’s exactly the atmospheric pressure that Musk is talking about in his Hyperloop paper.
Those are the kinds of inconsistencies that give me pause.
The anti-government hero
My main overall issue with this document is the “government can’t possibly make a a good design, a hero entrepreneur must step in!” vibe I get. This is much more true of the reaction that I see online in places like reddit than of the actual document, but it bugs me so I’m including it here. I’ve even seen claims that this will fail only because it will be too hard to satisfy any regulations (i.e.: the government will stop it).
I fear that this is going to lessen support for high speed rail at a time when it is uniquely well supported compared to anytime in the last 50 years. Keywords like “taxpayers” and fantasies about self-driving cars or flying cars (which have been “right around the corner” for quite some time) have killed support for transit in car-centric north america and this could continue that trend.
Details vs Cost Estimates
As I will explain below, and as others have explained, the level of detail and number of inconsistencies does not add up when compared to the confidence of the cost estimates. This is not all the fault of the authors, as the hype has kind of taken off with much critical discussion so far, I think in large part due to the entrepreneur worship culture I talked about above.
Not much to write about here, since it’s barely mentioned (the word is used 19 times). That’s okay at this stage, but it doesn’t really match the confidence in the price estimates.
Construction and Political Issues
From the intro section (which has no page numbers unfortunately):
Even when the Hyperloop path deviates from the highway, it will cause minimal disruption to farmland roughly comparable to a tree or telephone pole, which farmers deal with all the time.
First of all, “pylons the size of telephone poles” seems really optimistic. The installation of them would be much more intensive, and even people that are not directly affected by property issues tend to complain about things like eyesores and power lines during construction of above-grade railways. Also, based on all the renderings, they are much larger than telephone poles.
The majority of the route will follow I-5 and the tube will be constructed in the median
Maybe. But if you’re going to piggyback an existing structure, and disrupt a highway during construction, it’s probably going to cost you some money.
The tube will be supported by pillars which constrain the tube in the vertical direction but allow longitudinal slip for thermal expansion as well as dampened lateral slip to reduce the risk posed by earthquakes…Specially designed slip joints at each stations will be able take any tube length variance due to thermal expansion. This is an ideal location for the thermal expansion joints as the speed is much lower nearby the stations.
That’s a lot of thermal expansion between stations and I can’t think of other cases where longitudinal expansion is allowed over such a long distance. In 4.4.3, they propose a handful of stations which are mostly on branch lines. Even so, let’s assume there are about 5 stations along the 560km route, plus the two end stations. That’s six 93km sections of tube. Let’s assume the tube is fixed into place when the temperature is 20C. On a 40C day, the thermal expansion (at 13x10-6 mm/mm/K) along one length would be 24m. Presumably, it would be fixed in the middle of the section, and each station would have to accommodate 12m of expansion. In reality, higher temperatures are possible in California, and much lower temperatures are possible as well. Something like +/- 20m of expansion ability would be needed at each station (on both sides except for the terminus stations), and this is where you also have installed all of the hardware to speed up and slow down the pods.
Note that in the intro they state that rail needs “frequent expansion joints”, so they really are presenting the idea that they can avoid them and save money. In my opinion that’s a far-fetched claim given the design details presented.
Here I’m referring to the images in section 4.2.3, as well as the renderings in general.
Some legends or numbers would be helpful, and there’s not much to comment on without that. But let’s get back to the pillars. Unless there is some funky scaling going on, by comparing the tube diameter to the distance between pylons, this looks like only about 13m in between pillars. Other images also show a similar distance. Visually it just looks like a lot of pillars. Note: this would mean there are about 43,000 pillars in total for the main line. So what about those pillars?
First of all, for the distance in Table 6, a distance of 119km (minus 5.6km of tunnels without pillars), there are 3717 pillars in this section, or 30.5m between pillars. That doesn’t agree with the renderings or FEA images and is the kind of thing that makes me lose trust in the details that are outside of my expertise that I can’t really investigate. Note: this would mean that there are about 18,400 pillars total for the main line.
From the intro:
Tucked away inside each pylon, you could place two adjustable lateral (XY) dampers and one vertical (Z) damper.
OK, so now let’s look at the price: Based on a gut feeling that 30.5m between pillars just seems like a more realistic number than 13m, I’m going to use the number of 18,400 pillars. It looks like the FEA was done with the higher number, which leads me to think that the tube itself might be too weak to support itself over such a span, or that the vibration modes would be problematic —in short something doesn’t add up when you look at the number of pillars vs the design that they analyzed. Perhaps later I will do some FEA investigation of my own.
The total price for the pillars is given as $2.55B. For 18,400 pillars, that is about $140,000 each. Seems low to me considering they have damping in three axes as well as rollers or some other way to let the tube expand, but I don’t have an actual cost for comparison from an elevated rail system or something similar.
Using the 43,000 pillar estimate, that would be $59,000 each and a “no way”.
Lots of criticism has been placed on these in other posts and I don’t have anything new to add, but in my experience they tend to crash with varying distances or loads. I would really like, at the very least, to see some kind of small scale experiment with these and the compressor fan before everyone proclaims support for high speed rail in favour of this idea.
I think this will be a much more difficult problem than the paper hints at.
You need to ferry cars in this thing in order to sell it too? Just no. LA is one of the worst cities on the planet for public transportation and congestion and it doesn’t need a regular shipment of people in cars adding to that.
This isn’t a technical criticism but a note as an advocate for public transportation. Aside from my criticisms above, I’m glad this idea is adding to the conversation, but the idea that cars needed to be shoehorned into the project is counter to the overall purpose of public or rapid transportation.
Build local trains, bus rapid transit, or something at the same time. Who cares if the trip from LA to SF is fast if it does nothing to ease congestion and increase livability in the cities themselves?
This is a better takedown of the entrepreneur-worship angle:
My specific problems are that Hyperloop a) made up the cost projections, b) has awful passenger comfort, c) has very little capacity, and d) lies about energy consumption of conventional HSR. All of these come from Musk’s complex in which he must reinvent everything and ignore prior work done in the field; these also raise doubts about the systems safety that he claims is impeccable…
There is no systematic attempt at figuring out standard practices for cost, or earthquake safety (about which the report is full of FUD about the risks of a “ground-based system”). There are no references for anything; they’re beneath the entrepreneur’s dignity…
I have not seen a single defense of the technical details of the proposal except for one Facebook comment that claims, doubly erroneously, that the high lateral acceleration is no problem because the tubes can be canted. Everyone, including the Facebook comment, instead gushes about Musk personally. The thinking is that he’s rich, so he must always have something interesting to say; he can’t be a huckster when venturing outside his field.
And the cost:
And yet Musk thinks he can build more than 500 km of viaduct for $2.5 billion, as per PDF-page 28 of his proposal: a tenth the unit cost [of a high speed rail viaduct]. The unrealistically low tunnel unit cost is at least excused on PDF-page 31 on the grounds that the tunnel diameter is low…
people all over the Internet, including in comments below, defend the low cost projections on the grounds that the system is lighter and thinner than your average train. The proposal itself also defends the low tunneling costs on those same grounds. To see to what extent Musk takes his own idea seriously, compare the two proposals: the first for a passenger-only tube, and the second for a larger tube capable of carrying both passengers and vehicles. On PDF-pp. 25-26, the proposal states that the passenger-only tube would have an internal diameter of 2.23 meters and the passenger-plus-vehicle tube would have an internal diameter of 3.3 meters, 47% more. Despite that, the tunneling costs on PDF-p. 28 are $600 and $700 million, a difference of just 17%.
There’s more in the link about energy consumption and much more about the culture that allows the tube-dream of hyperloop to become the entire discussion over experts that have actually been doing this stuff for a long time.