Interesting link, thanks! I should have clicked more on the original article. :)
This seems to be the comment in question:
> This is worse than sideways acceleration: track standards for vertical acceleration are tighter than for horizontal acceleration, about 0.5-0.67 m/s^2, one tenth to one seventh what Musk wants to subject his passengers to. It’s not transportation; it’s a barf ride.
I find the statement that vertical acceleration is 'worse than sideways acceleration' to be highly suspect (otherwise why would you bother to bank into turns?) - I would guess that the track standards are for +/- 0.5ms^-2 and mostly target short-period up-and-down bouncing motions rather than smoothly applied upwards acceleration.
See https://pedestrianobservations.wordpress.com/2013/08/13/loop... linked from the original article.