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With test tracks and development consortia starting to pop up globally, the concept is certainly **coughs incongruously** gaining traction.
Though the idea itself is often pinned to Elon Musk (pursuing his quest to relearn the lessons of every terrestrial engineering development of the last 200 years), independent company Hyperloop One has been most visibly driving forwards with development.
The original idea should probably be attributed to British engineer George Medhurst, who could be called the father of the atmospheric railway (as they were long-known) and first filed a patent for a vacuum tube railway in 1810. This idea has been kicked about by many since then, including American and all-round tech aficionado Robert Goddard, who coined the term "vactrain" to describe the technology nearly a hundred years later.
On paper, the Hyperloop concept is a clever one, feeding off an extrapolation of Newton's First Law and attempting to remove as much air resistance as possible to limit the required driving force.
However, is this futuristic new transport system being overhyped?
I put the "fifth mode" statement in inverted commas not just because I am quoting it from Elon Musk himself, but also because it is a load of codswallop. The proposed technology is not revolutionary, simply comprising a pod elevated and driven forwards by magnetic levitation (maglev) in a tube pumped to a near-vacuum.
Nevertheless, Hyperloop has got a lot of people across the world talking about engineering and what the future of transport might look like, which is terrific. There are a lot of very clever people worldwide knocking their heads together, tackling technical challenges that may unlock other developments in engineering technology.
The trouble is, there are an awful lot of challenges to tackle, some of which probably kick this transport concept into the realm of fiction.
Firstly, the acceleration, top speed, pressurised cabin environment and associated emergency arrangements are all very similar to those utilised in commercial air travel. Nothing to worry about here.
The psychology of sticking a bunch of people in a tube with no windows may merit some further consideration, but even this isn't too worrisome considering the likely availability of wrap around screens that could emulate windows to the outside world. I'd hazard a guess that it would be no more claustrophobic than sitting inside a Pendolino at speed, with its tiny windows, low roof and gentle tilting as it goes around a bend.
The technology itself is old hat. Maglev has been in development as a practical idea for over a hundred years, and the vacuum tube is no more complex than a pipe with a big hoover stuck to it. The combination of the two is not remarkable, and Hyperloop One's DevLoop has quite comfortably shown this technological union in action.
Some of Hyperloop's progenitors argue that the engineering challenges are different from those on high speed rail and the two technologies therefore cannot be compared.
This is simply not correct.
If you have a vehicle sitting on a fixed track that guides its direction, then it is a form of railway technology no matter how you would prefer it to be categorised.
Even if you ignore the technological similarities, Hyperloop will be a land-based form of mass transit. What is the only other form of land-based mass transit? Yup, it's the railway.
(I'm considering buses, cable cars and personal rapid transit as being public but not mass transit for the purposes of this argument. They don't provide the "mass" people moving capacity of railway systems.)
Even Hyperloop One's recent promotional video draws comparisons between itself and high speed rail:
...only the smallest amount of electricity is needed to achieve extraordinary speeds and creates a more cost and energy-efficient system than high speed rail or airline transport
I'll get to the falsehoods in this claim later.
No matter how you look at it, Hyperloop is a form of railway system. It is also competing with existing railway systems. If it cannot prove that it is more economically viable than train travel, then it should go the way of previous attempts at maglev railways: nowhere.
I should point out that Chūō Shinkansen in Japan is an exception to this trend. It is the culmination of a heavily state-funded research programme that has been trundling along since the 1970s and is proving to be inordinately expensive to construct. It is planned to part-open for passengers in 2027, representing a 60-year development cycle.
Until the technology has really proven itself at full-scale, it is difficult to say with absolute certainty that the economics don't stack up. At this point, Hyperloop is therefore worthy of research and development.
However, just because the whole concept is still mostly restricted to the drawing board doesn't mean it isn't open to be assessed against the existing railway systems that it will largely mimic.
Railway alignments comprise interconnected straights and curves. The sharpness of these curves is dependent on the speed of the vehicles traversing it. For high speed rail, it's common for these curves to be 10km or more in radius, and that's only at 200 or 250mph.
Whilst the design of Hyperloop will likely permit tighter curves in relation to speed than the conventional railway, its pods will still be hurtling along at 700mph... That's at least three times the speed of the fastest regular high speed service.
Just like the conventional railway, Hyperloop will rotate the plane of its tracks as curvature increases (known as superelevation, or cant) to reduce the forces on passengers.
It is unlikely, though, that tracks could be tilted over enough to avoid the alignment being nearly dead-straight. The inertial forces on passengers will be like those in a jet airliner – when was the last time you were flying in a plane that tipped its wings over more than 45°?
The UK and mainland Europe are crammed with towns and topography; Hyperloop's alignment will invariably force its tubes underground into tunnels.
At which point we're back at a cost comparison of the different transport modes... Each of Crossrail's tunnels cost around £150m per kilometre; I look forward to the evidence that Hyperloop can beat this.
This is a great example of one part of the railway that still regularly goes wrong. Us railway engineers call them switches: where one track joins or splits away from another.
What makes them so complicated is the combination of different functions being performed by one single piece of kit. Passing trains impart huge forces on the underlying track, resulting in rapid degradation of the steelwork. The mechanism that moves the switch can be complex and cumbersome. There is also what's known as "detection", where the signalling system knows that the switch is set properly so that the correct signals turn green or red.
All these functions must work in harmony otherwise you just have a lump of expensive scrap metal holding up trains.
The basic mechanism of switches has been the same since we used wooden rails to move minerals around back in the 1500s, but even today Network Rail are still perfecting the design... Considering that the first modern railway line opened nearly 200 years ago, that is a very long development cycle.
To think that Hyperloop will have a solution that achieves these complex requirements the first time around, not to mention at six or seven times the speed of the fastest railway switch, is fanciful at best.
As the sun beats down on the vacuum tubes, the material that they are constructed from expands; tubes will get longer and fatter. This can be managed by using materials with a reduced thermal expansion coefficient and by constructing expansion joints between each tube segment.
However, these expansion joints would have to be strong enough to withstand the pressures from the vacuum within, increasing their cost greatly.
The other way around this is to bury the whole lot underground at inordinate expense.
Whilst it isn't a safety risk in isolation, the reliance on a vacuum to minimise air resistance is a problem when it comes to operational resilience.
In an emergency, or in the case of a pump failure, the Hyperloop tube will have to be fully recompressed (i.e. returned to atmospheric pressure): this shouldn't be a problem because all you need to do is open a valve to allow an ingress of air at a controlled rate. Easy.
The problems start when it comes to restoring the vacuum within the tubes.
Even if there were regular airlocks, you couldn't run a pod at speed from a vacuum into a section at atmospheric pressure: at 700mph this would have a similar effect to driving at 70mph into a concrete block.
There's a good chance, therefore, that pods will have to sit and wait, and it takes 4 hours for Hyperloop One to recompress/decompress their 500m-long test tube.
Undoubtedly there will be more powerful pumps in the final specification, but it is yet another bit of technology that requires radical development.
One of the big claims of all Hyperloop promoters is that their systems offer unbeatable energy efficiency. I'm not convinced.
Proven maglev systems (the Chūō Shinkansen is the most developed) use up to 3.5 times more energy than the equivalent high speed rail system.
Hyperloop's vacuum tubes will remove almost all aerodynamic friction, reducing the motive power requirements, but this will also increase the amount of power required to slow the pods down. With pods running through a vacuum, there will be no aerodynamic drag to exploit.
You will also have to power each of the pumps that maintain the vacuum along the length of the line; these pumps are unlikely to consume a trivial amount of energy.
The Hyperloop system represents a big pile of new technology, so the jury is still out on whether claims of superior energy efficiency are a complete fabrication. In any case, I'd love to see the calculations that prove its ascendency over high speed rail.
The Las Vegas to Los Angeles corridor is very much an inter-city offering... One that, with near-horizon technology, is best suited to a high speed railway. If funders were to be convinced to back an alternative, they would need proof that Hyperloop is the cheaper of the two options.
To do this, the cost must be lower per passenger than an equivalent high speed rail system.
Hyperloop One are on record saying that they aren't trying to compete with High Speed 2 (sorry STOPHS2, that bubble burst long ago), as they rightly point out that it has a good ten or so years of development behind it. However, seeing as it is at the cutting edge of conventional railway technology, I'll use its capabilities as a benchmark.
The peak capacity of High Speed 2 will be 20000 passengers per hour, in one direction. That's 18 trains departing per hour with 1100 seats each.
If Hyperloop pods have, say, 50 seats each, then to match the capacity of a high speed railway like High Speed 2 they would need to have 400 pods departing every hour. That's 9 seconds between every pod.
If we were to assume that you needed the same number of seconds to get off a Hyperloop pod as you need to get off a train, you would need 23 tubes to match the capacity of High Speed 2.
Even with some elaborate arrangement at the Hyperloop stations, no fewer than six tubes would be required to give a safe separation between the pods in case something went wrong.
And that's only in one direction.
Burying as many as 46 tubes in tunnels underground (with a suggested diameter of 4-5m each) isn't going to be very environmentally friendly and it certainly isn't going to be cheap.
Affordable Hyperloop infrastructure will never compete with the capacity of modern railway transport so can never be more "cost-efficient" than its conventional cousin, despite what Hyperloop One's marketing team would like you to think.
There may well be practical applications of the concept as a whole, too. Though the problems of limited capacity don't go away, connecting otherwise-disparate airports into one hub seems to be a potentially realistic proposal.
For now, the eager and exceptional minds in organisations like Hyperloop One will continue their quest for answers, and I for one will continue to watch with keen fascination.
This said, those in government or lobbying against high speed rail as being "out-dated" should remember that, today, the concept is little more than a privately-funded distraction.
Until this is no longer true, not a penny of public money should be diverted in Hyperloop's direction.
Let me know why... The best place to do this is Twitter, but I'll respond to emails too! The most interesting comments will be added below.
Gareth is an engineer and writer, specialising in railway systems. As well as roles in design consultancy, he has written for several technical journals and for the railway press. He leads the York section of his professional institution, as well as being a lecturer in track systems at a newly-opened national engineering college.
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