You're in control of your car though so if you need to you can stop and get out to deal with any bodily functions or sickness. You can't do that in this train. There's a lot to be said for the effect of just having the option even if you don't exercise it. Control is very comforting to people.

Not only comforting, the seemingly "rare" cases actually happen all the time and the advantages of being able to stop, go out, help the person etc. are effectively used all the time.

Designing mass transportation while ignoring such aspects is like programming without handling the limit cases "it works for N between 2 and 100 but not for 0, 1 and MAX_INT, even if these are allowed inputs." It's bad, very bad for the user, only an "astronaut developer" can love such a solution.

The first time a kid dies because it got sick the first minute of a 30-minute ride, the project is dead for good. Imagine the press, imagine the public response.

I can imagine entering the capsule to reach the international space station, preparing a whole year before. I can't imagine doing the same preparations for the ride between SF and LA. Give me the real train, thank you.

The Channel Tunnel between the UK and France works fine, and if someone got sick at the start of the tunnel section then there isn't too much that could be done quickly.

The public seems to have no issue with that concept, it is a simple risk that goes with getting on the train.

http://en.wikipedia.org/wiki/Channel_Tunnel

Yes, that's why we built that airport and hospital on the North Pole. Now intercontinental flights can make emergency landings in under 30 minutes at all times.

With multiple stations between SF and LA, this could be mitigated with an emergency system that pulls the train off at the next stop. Similar to how some buses or trains have emergency stop systems, except instead of stopping, the capsule would divert to the next station.