Fun Fact. From my "simple" calcs (going from 2011 to 2020 estimated) and using simple linear regression... In China they build about 2416.7 km of high-speed track a year.
So in the 6 days since this thread has started they have built about 39.727 km (24.685 miles) of new high speed rail track.
Source: https://www.forbes.com/sites/salvatorebabones/2018/02/13/chinas-high-speed-trains-are-taking-on-more-passengers-in-chinese-new-year-massive-migration/
What does that have to do with Hyperloop?
What got me thinking about it was Dave mentioning the Maglev in Shanghai. That was a one-off project and is only 30.5 km (19 mi) and is completed in 7-8 minutes. I was a bit curious if Dave ever got a chance to ride one of China's regular high-speed trains?
After watching thunderf00t's videos it made no sense to do hyperloop:
1: Take incredible amount of energy to get near perfect vacuum in such a large cylinder (100's km long) if even possible.
2: A catastrophic collapse, by nature, by poor design, by poor construction, or even man-made could cause immediate vacuum collapse.
4: If there was an accident, going 650 - 1000 km/h (~400-600 mph), most of the occupants would be casualties. How would you rescue them (have to decompression first). Remember the fire that happened on the Chunnel. At least they have a middle service/rescue tunnel and at 100 000 Pa (~1 Atmosphere).
5: If there was even one accident in which multiple casualties, then the hyper-loop system might be abandoned. Remember what happened to the Concord.
6: How are you going to have expansion gaps in a vacuum tube? Steel when heated, causes tremendous pressures. You have 11um (11 micron meters) of expansion for every meter per degree C. So let say when they constructed the HYPE-erloop at 20 C (~70 deg F and it went to 38C (~100 deg F) and you have 10km (~6mi) of tubing. You would have 11 µm/(m °C) * 10000(m) * 18(°C) = 1.98m (about 6.5 ft) of expansion that needs to be taken into consideration every 10km. This is why bridges and train tracks have gaps. Gaps are much harder to do when you have to maintain near perfect vacuum. If the temperature goes down then you have to take into effect thermodynamic contraction also. The pressures created by this expansion (if steel is constrained) would be enormous (think Hydraulic Press Channel stuff).
7: This is untested tech at this scale. So chances are the 1.5x, 2.0x, 2.5x or even 3.0x than their estimated costs and there is always the possibility of it not being possible in the end (think of like a large military weapon system that got axed xx% of the way through the project). In the end would it be economically feasible compare to air travel (can it really compete).
So I kind of agree with Dave and Thunderf00t on this, this just seems like such a boondoggle so why don't you just go regular high-speed rail.
Catrostrophic collapse of vacuum
https://youtu.be/Z48pSwiDLIM?t=564Example of Thermodynamic bending of railroad tracks (likely did not have enough track gap length to account for expansion)
https://upload.wikimedia.org/wikipedia/commons/b/b8/Rail_buckle.jpg