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Why the Biggest Obstacle for Elon Musk's Hyperloop Might Be Tunnels

Illustration for article titled Why the Biggest Obstacle for Elon Musks Hyperloop Might Be Tunnels

It all sounds so Jetsonian. A new 600 mph "Hyperloop" method of transportation connecting Los Angeles and San Francisco? That's the buzz around the internet water cooler as people guess what Elon Musk has in store for the transportation of tomorrow. I say, sign me up! But if we take any lessons from past visions of futuristic transportation (as we are wont to do here at Gizmodo) we can probably guess the Hyperloop's greatest hurdle: tunnels.

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Nobody but Musk knows what his proposed Hyperloop transportation system might look like. We've gotten hints that it's supposed to be "a cross between a Concorde, a rail gun and an air hockey table." But despite some random online guesses partially validated by Musk himself, no one will know for sure what Hyperloop is until maybe August 12th. What we do know is that anything he proposes won't be easy without some drastic cost-cutting improvements in the way that we dig tunnels. Because not only are tunnels a necessity, they're also incredibly expensive.

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Hyperloop Needs to Go Underground

A couple of months ago, Business Insider was the first to point out that Musk's proposed transportation system (well, what little we knew about it) sounded like something that had been studied at the Rand Corporation back in the summer of 1972. Rand looked at what was called Very High Speed Transit (VHST), which would provide a network of futuristic underground trains, allowing people to travel between Los Angeles and New York City in less than half an hour.

This VHST would be traveling at speeds as high as 14,000 miles per hour and would be expandable. The proposal included stops in Amarillo, Texas and Chicago, Illinois and from those four major hubs people could one day travel to other major cities in the U.S.

The Rand study raises some of the same issues that will likely become problems, should Musk's plans make it beyond the concept stage. The first is that anything this fast (600 mph if you want to get between L.A. and San Francisco in just 30 minutes) can't have any dramatic turns unless you want people vomiting constantly.

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"The most demanding technical problem is that of lateral accelerations. A vehicle traveling at 550 mph cannot undergo sharp turns," the 1972 Rand study explained. "This requirement imposes strong constraints on the design of the guideway and would create a great difficulty if one attempted to run the VHST above ground."

This, of course, is a problem for anything running in America's most populous state between America's second most populous city and America's fourteenth most populous city. There are a lot of people and trees and roads and McDonald's between L.A. and San Fran. Barring a strange loop out into the ocean, you have to go underground.

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And if Hyperloop has to go underground, that means any money saved by the tech won't make up for the fact that the highest costs for this kind of infrastructure have to do with digging the tunnels. As the Rand study put it:

Once the assumption is made that underground tunnels are necessary in order to travel at speeds competitive with present (and future) aircraft, another aspect of the problem becomes evident. Over 90 percent of the system cost will result from the tunnel itself.

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Ninety percent of any system that's sure to break the billion dollar mark isn't exactly chump change. But we've known, even before the 1972 study, that finding ways to more efficiently dig tunnels would be vital for transportation systems of the future.

The Retrofuture of Digging Tunnels in "Our New Age"

Back in 1969 the academic, inventor and popular futurist Athelstan Spilhaus imagined that if we could just find more efficient ways to burrow through the earth, the transportation of the future would follow right behind.

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Spilhaus wrote a comic strip called "Our New Age" that was started shortly after the Russians launched Sputnik in 1957. Why would a respected academic launch a newspaper comic? Because he was concerned that kids of the time (those darn Baby Boomers) weren't showing enough interest in science. "Rather than fight my own kids reading the funnies, which is a stupid thing to do, I decided to put something good into the comics, something that was more fun and that might give a little subliminal education," Spilhaus would explain years later.

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Illustration for article titled Why the Biggest Obstacle for Elon Musks Hyperloop Might Be Tunnels

His November 16, 1969 edition of "Our New Age" looked specifically at the tunneling of tomorrow. Cheaper methods of tunneling — what he called a "mechanical mole" — would let the transportation of tomorrow become subterranean. The noise and pollution of the modern city would conveniently become hidden away, deep underground.

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In the future, these mechanical moles would become much more powerful, drastically reducing costs for anything from subways to underground auto-tunnels to, yes, a Hyperloop.

Illustration for article titled Why the Biggest Obstacle for Elon Musks Hyperloop Might Be Tunnels
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Of course, finding cheaper methods of tunneling isn't the only hurdle for making the hypothetical Hyperloop happen.

There are all kinds of reasons that brilliant technology doesn't take off: lack of consumer demand, access to capital, and the political realities of building something that affects so many people, businesses and municipalities. What happens when any of the dozens of towns along the proposed route won't allow tunneling construction without a stop being placed for them?

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We have the technology to make jelly beans taste like freshly mowed grass, rotten eggs and ear wax. I know, because I tasted them. But not surprisingly, there's very little demand for these flavors outside of kids who want to play Harry Potter Mouth Roulette. Just because the technology is there doesn't mean it's going to be successful.

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Musk's back-of-the-napkin designs for a futuristic method of transportation are more than welcome. We need more visionaries in the world who embrace the techno-utopian idealism that pushes humanity forward. But Musk's strong suit has always been surrounding himself with incredibly intelligent, driven people and then getting things done. Musk knows as well as anyone that tremendous political obstacles can derail a good idea. But speaking as a purely selfish entity who would love to travel between L.A. and San Francisco in the amount of time it takes to watch a sitcom, here's hoping this one has enough momentum to stay on track.

Images: scanned from the November 16, 1969 edition of "Our New Age"

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DISCUSSION

renniSaint
renniSaint

I thought about writing a post about this whole Hyperloop thing because I am a tunnel engineer designing subway tunnels and also work with a lot of the people designing the CA High Speed Rail. Unfortunately, I'm not a very good writer so I guess I will just comment here.

First, lets look at what Mr. Musk has said about the project:

1. It is an approx. 2m, non-vacuum tube system (making supersonic basically impossible as far as I can tell)

2. It is unscheduled (so small, 4-6 person cars)

3. SF to LA in 30 mins (do the math and you have to average at least 600mph)

4. Cost will be $6bil (cheapest you could ever hope to build a basic tunnel for is about $70mil a mile and that is being very generous, so no way tunnels are involved)

This leads to some rather obvious conclusions about the system that rapidly appear to paint the project into an engineering corner I can't figure out how to escape from.

First lets look at the horizontal alignment this project would take. If you are traveling at those speeds you need something like a 50 mile turning radius so people don't puke everywhere. This means you cannot use any existing public right-of-way or utility corridor that means buying land. Even assuming you can somehow buy just a 5m wide swath through from downtown LA to downtown SF you are talking right of way costs being at least $20bil at only a dollar a foot so...... not sure how that works. Second lets look at vertical alignment, again, because of the speeds involved any attempt at following existing topography are going to kill the occupants in a most spectacular fashion, this means you will have to mount the tubes on a system of piers and tunnels, piers become in issue because of wind, thermal, and seismic displacements, any significantly tall structure sways and moves because of wind, solar radiation, and weather effects, not a lot but when you are traveling close to mach 1 any tiny non-linearity will make for the worst ride ever. Finally seismic affects seem like only an issue during earthquakes, not so, the San Andreas (and many other similar fault systems) are creeping slowly causing significant displacements across the fault without any discernible shaking or "motion" this means realigning your tubes constantly or not crossing any faults (good luck). Tunnels actually aren't that bad an idea other than the cost... Seismic issues are not as big as one might think mostly because of the way energy from an event travels. Surface waves (what us humans feel) travel along and dissipate at a square rate like ripples on a pond. Body waves (which is what affect tunnels) dissipate at a cubic rate which means you can be much closer to a seismic event and have much less damage. Finally, tunnels being tubular in shape are pretty excellent geometrically at withstanding seismic forces and letting them just roll right on by.

So we have basically ruled out at/above grade alignments, what about underwater? Well, there you run into your own special host of problems but also some neat potential benefits. First is the obvious issue again of not being able to follow floor topography so you are going to have to do a tethered floating system. But with any tethered system you have an extremely difficult time keeping everything perfectly aligned. Second, probably bigger issue is if anything goes wrong you are so epically SOL that I'm not convinced anyone would want to use this thing. On the other hand there are some fun benefits to this solution. First is energy savings, if you go sufficiently far out and get away from the continental shelf you can actually start to use a gravity based system whereby you drop to extreme depths in the middle of your run using the downhill to accelerate through the first half of the trip and the uphill to decelerate during the last half of the trip. This approach works much better in an evacuated tube, but it definitely doesn't hurt. In fact it is extremely common in modern subway designs. Only problem with this is of course at the depths required to get a significant benefit you are talking about needing one heck of a tube able to withstand hundreds of atmospheres of pressure. And if you are building a tube that can withstand hundreds of atmospheres of pressure, why don't you just make it one more atmosphere and evacuate the thing so you don't have to fight air friction the whole way?

So we are back to underground. Here again, you can use gravity as your accelerator and the nice thing is while your stresses get higher the deeper you go the bedrock will generally carry the load so you don't really need to worry too much about building super beefy tunnel structures, groundwater also cannot generally penetrate too deep so you aren't going to have massive pressures building up from water. Really the biggest drawbacks to underground are cost, and time. Cost we already discussed but what most people don't realize is how long tunneling takes. If you are moving really really really fast you might be able to average 30 feet of tunnel a day. Lets say Mr. Musk has invented something amazing and now they can go 50 feet a day. With one machine they would be able to have one LA/SF tunnel done in a speedy 80 to 90 YEARS. Don't forget you need two tunnels for two way traffic. Obviously you would use a lot of machines to dig the tunnels but then you start incurring massive costs. Each machine costs around $50-100mil depending on size/options and then you have to procure it. Surprisingly (that's sarcasm by the way) tunnel boring machines aren't exactly off-the-shelf items. Each TBM is a completely custom, one-off item so if you want to get your tunnels done in ten years you are talking about 16 machines at a cost of nearly $1bil assuming they give you some sort of bulk buying discount. Procurement time will likely be in the five to ten year range as TBM companies aren't exactly set up for that size order. So now you are looking at taking 15 to 20 years to build just a SF/LA line which requires a solid $50bil investment. Now, you may be wondering why the costs are so high and it takes so long. One of the funny things nobody ever thinks about when they talk about tunneling is the stuff that has to come out of the ground to make a hole. For the two tunnels you will extract a 1,000'x1,000'x1,000' cube of ground up rock. That doesn't sound like a lot until you stop and think about moving that much material through two holes each the size of a set of double doors. Another way to think about it is moving a 70'x70'x70' cube through those same doors every day for ten years. Or, a 6'x6'x6' cube every minute of every day for ten years. It starts getting a bit scary when you start trying to figure out what to do with all that material.

Anyway, so here I am completely and utterly confounded by how he thinks this will work and with my own ideas about how to actually do it.... But not for $6bil....