I've been meaning to post this last week, but forgot. Hyperloop is a proposed new transportation system designed by Elon Musk, which focuses on small capsules traveling at high (up to 1200 km/h) speeds through partially evacuated steel tubes. There is a proposal available online. I believe it's all crap, and I'm going to explain why.
Now, first of all, there is of course a chance that this blog post will look very embarrassing twenty years from now. One dismisses the founder of PayPal, Tesla motors and SpaceX at one's own peril.
But on the other hand, it's not like this hasn't been tried before. Right from the moment the first trains appeared, people said "I can do better than that" and invented their own 'improved' designs. The Wuppertal Schwebebahn is a rare example that was actually built and then actually worked (and still does). Hyperloop's approach in particular is very similar to a previous Swiss idea. However, that swiss idea did not have a compressor and was built in tunnels instead of elevated, and relied on much larger trains.
A more useful comparison is the Transrapid, a german high-speed Maglev train. It is beyond any doubt the world's most successful high-speed Maglev train, because there exists one commercial installation, as an airport shuttle in Shanghai. Despite several decades of research and development, and the proof that the technology can work both in theory and in practice, the system has been ultimately abandoned and was really a waste of everyone's money. Hyperloop is technologically very different from Transrapid (for one, it is not a MagLev train), but many of the challenges are similar.
Can it work?
I have no idea whether the approach is actually workable. I seriously don't know enough about any of the involved technology to say so. So I'll have to give Hyperloop the benefit of the doubt and say that it probably can work from a technical point of view.
A railroad is not an island
That doesn't mean it's a good idea, though. The proposal focuses almost only on the technology, and does not discuss at all how to actually build a useful transportation system. An example:
The calculation presents two different models: One that is for passengers only, where the capsules have an exterior width of 1.4 m and height of 1.1 m, and another larger one. The smaller one relies on gullwing doors and seats that basically have the passengers lie down. Its main advantage is that it is a lot cheaper. Its main disadvantage is that it is illegal.
The reason for this is that such a system isn't wheelchair accessible, because there is no space for a person seated in a wheelchair. We have thankfully finally gotten used to the idea that access for persons with reduced mobility is not something optional, but an essential part of preserving human dignity. It is neither realistic nor desirable to assume that the state of California would make an exception here.
Any actual transportation system (as opposed to a giant model railroad, which is what the current Hyperloop proposal shows) needs interfaces between it and the people who want to use it, or in other words, stations. These are not a thing that just happens, but rather an integral part of the overall design, and they require that you give them a lot of thought.
Hyperloop really doesn't. It gives a vague explanation of the proposed experience. However, it lacks any details. Will there be shops? Parking spaces? Will stations be located in city centers, or on the outskirts? What about connections to existing rail systems, trams, or buses? What about evacuation in case of a fire, or about people opposing the construction? All these are real, important and expensive concerns. Just ask the people building new transportation hubs in Stuttgart or Berlin…
All the people who try to reinvent trains sooner or later hit upon a simple fact: The standard railroad switch is totally amazing. It requires only the space for the two tracks, and only a very tiny part of the overall construction has to move. They can change directions in about ten seconds. Any monorail approach has to either replace a part of the track, or bend it to a new direction. The Wuppertal Schwebebahn I mentioned above replaces the track; the Transrapid bends it. Both take much more energy and time.
Hyperloop hasn't hit on that fact yet; reading the paper, it seems that the authors simply assume that switches exist, without thinking at all about it. That is dangerous, because a switch for Hyperloop may be the most complicated kind of switch invented yet. Not only does it require very large turning cycles, it also has to be completely air tight at either end, and you either have to keep the vacuum while it is switching, or restore it after you're done. Switches are definitely necessary on this system, because there are several proposed spurs to minor californian cities.
Note that switches also have to be incredibly fast. Specifically, after a pod has cleared the switch, it must have completed its direction change before the next pod would have to start breaking in order to stop before the switch. This is because one cannot send a pod towards a currently changing switch, just hoping that it will be in a valid position when the pod arrives. This is completely unfeasible at the maximum 30 second distances between pods; one would have to group them by destination and leave a gap in between.
You just have to love the chapter on safety. It's basically three paragraphs going "yeah, this is basically safe, so there". There are no points on procedures or technologically, just notices that the track is completely enclosed, that trains can't be accelerated to unsafe speeds, and that there are no pesky humans interfering. That is completely unacceptable.
How is train separation achieved? You can, of course, easily send pods through a tube at 1000 km/h in two-minute intervals and just hope that they all come back out in the same order. The authorities might even allow it if you pay enough bribes and don't want to carry people. In real life, every capsule needs to be able to come to a controlled stop if the capsule before it does not clear the area it is currently at in time. If the system assumes thirty second headways at peak times, that means a capsule must be able to come to a complete stop within thirty seconds (because after that it would be where the stopped capsule is now). At 1200 km/h (= 333.3… m/s), that works out to a minimum emergency brake deceleration of 11.1… m/s, or slightly above 1g. In reality, you'd want some additional buffer, which only increases the forces. Those seat belts in the pods turn out to be absolutely essential. Note that the proposal includes no specification for the braking system whatsoever, only a cost estimate of more than $70,000.
All this assumes a totally safe communications system that works at these speeds and these distances. This isn't a technical impossibility, but it is not going to be cheap either. For comparison: The vehicle-side interface for ETCS, the new european train control system, comes to about 200,000 € per locomotive if you can find it really cheap.
The environmental impact discussion is even worse than the area on safety. It simply assumes that nobody in California will have any problems with the world's highest pipeline passing through or near their back yards. That is rather optimistic. Bundling most of the track with a motorway is a nice solution, but not an option in built-up settlements, where other alignments need to be found.
While we're on the topic of alignments: How will the system reach its stations? For normal high speed rail, that is easy: The tracks and stations are already in place. This is not true for any new system which needs to either cut through a lot of houses or build very expensive tunnels. The tunnel solution is favored for new high-speed rail stations in city centers, e.g. London St Pancras International. Like any tunneling, it has a tendency to drive the costs up significantly.
The capacity of the system is at the low end average for high-speed rail. The proposed smaller system has a target average of 840 people per hour; for rush hour, that can be increased by a factor of four (to 3360 people per hour). For comparison: The low end is about equal to what currently drives on the Paris-London Eurostar line, an altogether very under-utilized system. In Germany, the Cologne-Frankfurt high speed line (itself not exactly bustling with activity) has a capacity of about 2800 passengers per hour at the current timetable, although lack of trains may make that difficult.
However, trains scale much better. There is no particular reason why London-Paris can't see the same number of passengers as Cologne-Frankfurt, and both could easily deal with twice as many passengers, too. The upper end currently seen in Europe would be the french high speed network, which can see trains composed of two double-deck TGV units every three minutes in the best case. This works out to an average peak capacity of more than 20,000 passengers per hour. This is probably not actually sustained for an entire hour. Still, the system scales relatively gracefully to very high numbers of passengers, while Hyperloop has a hard limit not all that far from current standards.
The cost suggestions are incredibly ambitious, or in other words, not even remotely accurate. Missing are items like a safe communication and control system, switches, any sort of traffic control, station development and so on. The running costs have been completely ignored (other than amortization of the investment). Also ignored: Any cost for testing and system development. For the Transrapid, that cost was on the order of a billion euros.
I am also not convinced that the costs that have been calculated are accurate. The pod, for example, costs less than half of a modern regional-service DMU (those tend to cost more than $2 million a piece). While the pod it is smaller, it requires pressurization and a lot of new and untried technology. Perhaps a more useful comparison would be a business jet, which is also pressurized (but with a far lower pressure difference), small, and contains a lot of expensive technology. That makes the price for the pod seem even more unrealistic.
Hyperloop is an interesting technological toy, but it is very far from an actual transportation solution, and I am not convinced that it can ever get there.