What if we fill the whole tube with carriages, without any space between them and very little space between the carriage wall and the tunnel wall? That would le

What if we fill the whole tube with carriages, without any space between them and very little space between the carriage wall and the tunnel wall? That would leave much less room for turbulence and perhaps reduce friction. If that works, you could then have "station" sections where you could place/remove "inner" carriages to/from the carriages running inside the loop and thus you'd never have to disconnect the main carriage loop.