Hyperloop: Terrifying Thrill Ride, or Serious Transportation Proposal?


After a couple months of teasing and putting the "hype" in "Hyperloop," Elon Musk recently took the wraps off his proposed ultra-high-speed transit system. The proposal is to put a pair of pipes between Los Angeles and San Francisco, pump out 90% of the air, and shoot capsules through at 700 MPH. Musk's claim is that the system would cost $6 billion, take 30 minutes to make a one-way trip, and could be built in a decade or so.

I was disappointed to read the "analysis," which struck me as very superficial for the dramatic claims being made. The cost estimate, in particular, seems wildly off-base: I don't see what would enable Hyperloop to be built as an elevated system for less than a tenth the cost of a ground-level bullet train using proven technology. It seems fair to assume that where the bullet train has gone through detailed engineering design and cost analysis, the Hyperloop cost is (at best) a back-of-the-envelope calculation using some crazy optimistic assumptions.

There are other problems with this proposal (and I'll summarize some at the end of this article), but the biggest flaw, in my mind, is that there seems to be zero consideration for passenger comfort.

The passenger capsule would seat 28 people in a 2x14 configuration. The exterior cross-section of the capsule is six feet high by a little over four feet wide (the interior cross section isn't specified, but is probably no greater than four feet by four feet). Assuming that there's no interior aisle, that gives you a little wider seat than in economy-class on an airplane, but no ability to get up and move around once the capsule is closed. There's no bathroom on board (presumably you're expected to hold it for the 30-minute trip), and presumably no cabin attendant since a crew member wouldn't be able to get back to a passenger to help with anything.

Once underway, the capsule would be subjected to up to 1g of acceleration and deceleration, and 0.5g of acceleration around corners (which passengers would feel as about 1.1g of vertical acceleration as the capsule banks). The lateral acceleration is significantly more than you would feel in a commercial airliner, and is more like what you would experience in a thrill ride. The vertical acceleration is within the 0.75g - 1.25g envelope of a typical airline flight. However, the proposed route appears to go directly from straight to a full 0.5g turn, so passengers would experience a sudden "snap" as the capsule banked and accelerated into and out of a turn. More gentle entry and exit from turns would eliminate this problem, but also impose significant new route constraints which would almost certainly drive up the cost.

Furthermore, the capsules would have no windows and be traveling through steel tubes, so passengers would have no way to see out. While Hyperloop promises that every seat will have an entertainment system, many people will be very uncomfortable if they can't see outside. Claustrophobia aside, subjecting someone to significant accelerations and rotational forces while removing any external visual reference is also an efficient way to induce motion sickness. Given that, windows and a transparent tube seem like necessities not frills. I don't know how much that would add to the cost, but it doesn't seem like a small number.

So the Hyperloop experience would be something like this: you board at the departure station and get strapped in, and the station crew closes the door and seals you in with 27 other people in fairly tight quarters. Once the door is closed, you cannot get up and move around until arrival, and there is no cabin attendant. You can't see anything outside the capsule (though your entertainment system may show you a virtual landscape whizzing by), and you will feel a series of fairly strong accelerations and sudden banking motions, comparable to a roller coaster. There will be fairly constant noise and vibrations (similar to an airliner) from the compressor driving the air bearings. If anyone gets sick (which seems likely), there will be no opportunity to clean up or rearrange until arrival.

And that's if everything goes well. If there's an emergency, your capsule will be brought to an unexpected stop, and someone will tell you over the radio to stay calm and don't get up. You will be stuck in the capsule (there's not enough air to breathe in the tube) until it can be brought to an emergency egress station.

That might be fun an amusement park, but not for a transit system.

Other Issues with Hyperloop

Other commentators have raised a number of other concerns with Hyperloop. Sorry for the lack of linkage, but here's a summary of what I've read elsewhere:

  • The cost estimates seem wildly low compared to the real-world costs for similar types of infrastructure projects. Musk claims that elevating the pipes on pylons will be cheaper than building the system at ground-level, but in the real world elevated systems are always much more expensive.
  • Hyperloop, as proposed, would have a capacity substantially less than the California bullet train in terms of passengers per hour. The small (28 passenger) Hyperloop capsules would need to run unrealistically frequently in order to get any reasonable system capacity as compared to a bullet train which can carry over 1,000 passengers.
  • Musk's proposal only considers the initial capital expense of building the system, and does not look at any of the ongoing operational expense and maintenance. Even if Hyperloop is cheaper to build than a bullet train (a dubious claim), it may be more expensive to operate.
  • There's almost no consideration of failure modes and what to do in an emergency in Hyperloop. Musk claims that the system would be impervious to weather, seismic events, etc., but there seems to be no allowance for mechanical failure, onboard fire, power failure in a capsule, etc. The atmosphere inside the Hyperloop tube would be considerably thinner than outside an airliner, meaning that exiting the capsule outside a station is not an option, and any pressurization failure is much more serious.