“Barf Ride”

Alon Levy has exactly the technical critique of Hyperloop I was looking for. It’s scathing, as one might even expect:

The barf ride that is as expensive as California HSR and takes as long door-to-door is also very low-capacity. The capsules are inexplicably very short, with 28 passengers per capsule. The proposed headway is 30 seconds, for 3,360 passengers per direction per hour. A freeway lane can do better: about 2,000 vehicles, with an average intercity car occupancy of 2. HSR can do 12,000 passengers per direction per hour: 12 trains per hour is possible, and each train can easily fit 1,000 people (the Tokaido Shinkansen tops at 14 tph and 1,323 passengers per train).

But even 30 seconds appears well beyond the limit of emergency braking. It’s common in gadgetbahn to propose extremely tight headways, presuming computerized control allowing vehicles to behave as if they’re connected by a rod…. In reality, such systems have been a subject of research for train control for quite a while now, with no positive results so far. Safety today still means safe stopping distances. If vehicles brake at a constant rate, the safe headway is half the total deceleration time; if a vehicle brakes from 1,220 km/h to zero in 60 seconds, the average acceleration is more than 5 m/s^2, twice the current regulatory safety limit for passengers with seat belts.

There’s a lot more of this sort of technical analysis, which Musk (for whatever reason – FUD? Indifference?) apparently couldn’t be bothered to do. But it’s his own project!

Ultimately, I do honestly think the idea of pneumatic rail has some merit, even if it is as expensive as HSR, if its proponents are willing and able to build it directly between city centers and satisfy the more fundamental engineering problems of needing a basically laser-straight horizontal and vertical line across California (which Hyperloop isn’t, and necessarily must be). But that’s a lot to ask of this design, and Musk elided over all of those problems in his proposal.


~ by J.D. Hammond on August 14, 2013.

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