Hyperloop

The Hyperloop is a proposed "fifth mode of transport" (the other four being planes, trains, cars, and boats) that was unveiled by Elon Musk in 2013. It involves a tube evacuated to very low pressure in which pods are propelled forward, using magnets, at speeds in excess of 1000 km/h. In essence, it is a pneumatic tube on steroids or a magnetically levitated train inside a vacuum tube. Whether or not the Hyperloop proposal will come into fruition is highly doubtful, since it was based on a one-man troll campaign.

So how was this supposed to work?
Any intelligent fool can make things bigger and more complex, it takes a touch of genius and lot of courage to move in the opposite direction.

Most of an Earth-bound vehicle's energy is used to counteract the forces of friction, gravity, and atmospheric drag. Without these, anything moving keeps moving indefinitely. So the idea is that one removes the atmosphere, and uses some system to levitate the vehicle slightly above the ground. Existing trains levitate using magnets. The original design of Hyperloop used an air cushion instead, though recent Hyperloop designs use a combination of maglev and a partial vacuum. Both designs require a tube that is airtight for hundreds of miles, and a vehicle that is airtight as well. In the event of a catastrophic failure of either capsule or tube, the low pressure would of course become a huge problem. If the tube gets punctured, a lot of air is going to collide at very high speed with the capsule. If the capsule is punctured, all the air will be pushed out, leading to depressurization. Musk's proposal called for oxygen masks, but these aren't foolproof, and won't help with the other issues experienced in a depressurization accident, like water on exposed body parts (eyes, mouth, airway) boiling away. Depressurization can, as many people know, occur in aircraft accidents, but aircraft can quickly descend to a safe altitude if this happens. You could design a system to repressurize the tube in the event of an accident, but this adds more complexity, as well as the possibility of it malfunctioning, which is a Bad Thing if it happens while a capsule is traveling through the tube.

Musk's proposal called for relatively small capsules, seating less than 30 people, but headways as short as thirty seconds. A 30-second headway is something even modern subways don't do, mostly because loading and unloading passengers takes longer than that and also due to safety considerations (30 seconds is just not enough to safely stop if the vehicle in front stops). Of course, the loading and unloading problem could be solved by having several parallel loading areas (i.e. platforms) that somehow merge to the main tube, but Musk never answered the question of how exactly merging and branching would work either.

So does this actually work?
In short: it wouldn't. While some of the inherent design problems might be fixable, their combined magnitude would make it an economic impossibility to build. And that's before one takes land costs and other minor details into account. And that's not even getting into the political difficulties behind getting large-scale infrastructure built, especially in the U.S. Then there are the engineering problems like dealing with the capsules heating up from air compression (as the tube will not be a total vacuum), or the tube needing sub-millimeter tolerances. Sub-millimeter tolerances are not that difficult to achieve, but doing so is expensive and maintaining it over hundreds of miles is a major headache. Oh, and then you have to deal with earthquakes, especially in California, or even just simple thermal expansion of the tube and capsules. And it's unclear how the proposed thirty-second headway was supposed to work with the proposed 0.5g braking deceleration, given that at the proposed top speed of 1220 km/h, there is not enough space or time for a capsule to brake before it slams into a capsule that experienced catastrophic failure in front of it. Not to mention that even at the blatantly unrealistic headways that Musk proposed, Hyperloop would have a capacity of less than a third that of high speed rail (HSR).

Also, Musk's proposal envisioned building a system not directly between downtown Los Angeles and downtown San Francisco, but instead from Sylmar to somewhere in the East Bay, which means that one would still have pretty much the same problems as with air travel. The ride itself is supposed to take only half an hour (at Musk's fantasy estimates), but unless that precise suburb is one's final destination, then one would spend an hour or more getting to one's actual destination. There is a reason why HSR kills competing air service even at two hours' travel time. You see, land downtown is expensive. And more people who could have stilts in their front yard means more NIMBYs trying to derail one's project. California HSR costs as much as it does in part because it goes downtown instead of considering getting people to their final destination "someone else's problem". To add insult to injury, Musk proposed including TSA-style nut-grab brigade security theater, so taking the Hyperloop instead of Southwest Airlines wouldn't even spare one from that. How Musk planned to secure hundreds of miles of tubing against terrorists was also not explained.

What was Musk's intention in promoting this?
First of all, the proposed route links — by sheer accident, of course — the place in LA closest to Musk's home at the time to the place in the Bay Area closest to Musk's then-workplace at Tesla. And given the way Musk bashed California HSR when he announced his project, it is not unreasonable to assume that part of his intention was to keep the latter from getting built. Unsurprisingly, a favorite line of attack by anti-HSR people in California become "bla bla bla Hyperloop is cheaper bla bla Hyperloop is better bla bla Elon Musk is a genius". Of course, the fact that Elon Musk has been has nothing to do with any of this.🇱🇮

In March, 2018, the city of Cleveland, Ohio, inked a $1.2-million feasibility study of the construction of a between it and Chicago, Illinois. Not surprisingly, critics voiced their concern that the technology does not even exist yet, which Hyperloop Transporation Technologies admits. On the bright side, if investigators conclusively show the proposal to be unrealistic, it could potentially pave the way for the construction of a high-speed rail network in the Midwest, currently in need of an economic stimulus. By 2022, it had become apparent that Musk's hyperloop was an attempt to get California to cancel its plans for high-speed rail, and was wasting government money on feasibility studies. Why was Musk trolling like this? Probably because of his personal dislike for public transport, and Tesla's financial interest in quashing public transportation projects.

Similar things
As you may know, similar proposals have been made in the past and some have actually gotten built, be it a in New York, a  in London (which both got built), or  in Switzerland (which didn't). If you notice a trend in none of them managing even five years of operation, you might be on to something. However, the idea of a where the tube would contain a true vacuum and the propulsion would be through  has been suggested as a possible future replacement for high speed rail and airplanes (with minor practicality issues related to putting a space shuttle inside a giant inside-out space station with the tiniest leak in either meaning everyone dies horrifically). Therefore, there are some who argue that Musk's troll campaign is actually good (if not all that original) but just too far away from realistic completion to be of any use now. This dramatically contrasts with high speed rail or even technology, with actual lines in revenue service.

Prototype Capsule
In October 2018, Hyperloop Transportation Technologies (Hyperloop TT) unveiled its first full-scale Hyperloop capsule in Spain. The capsule is made out of a composite material called Vibranium (after the fictional Marvel supermetal, because of course), 82 carbon fiber panels, 72 sensors, 75,000 rivets and 7,200 square meters of fiber. Hyperloop TT will next send it to France for additional testing and optimization before letting it run on commercial tracks.

DC/Baltimore Loop
On April 17, 2019, a U.S. federal agency released a roughly 400-page report detailing its in-depth investigation into the human and natural environmental impacts of Musk's proposed 35-mile loop between Washington, DC and Baltimore, MD. Its contents reveal a much more scaled-back, not-so-"hyper" version of the Hyperloop originally envisioned. Rather than speeding commuters between the two cities along at 1200 kph in a vacuum-sealed Vibranium pod, the proposal outlined in the draft Environmental Assessment describes driverless, battery-powered vehicles being lowered into one of two ventilated tunnels, and travelling down them at 240 kph for a ~15 minute journey. Due to station capacity limitations, usage would be initially capped at approximately 1,000/day, roughly the equivalent of a single double-decker MARC train (which, in comparison, takes about 55 minutes to make the same journey with five additional stops, and is one of several train and intercity bus routes already between the two cities). There is no official cost estimate as of writing, and approvals are still required from a half dozen agencies and state DOTs, so prospects are still shaky for the project.

While some dupes, like former Maryland governor Larry Hogan, were gung-ho about the project, others are not so on board. Virginia Chief of Rail Transport Michael McLaughlin, after being taken on a demonstration ride in the California test track, noted that it was basically just "a car in a very small tunnel."