SFGTV December 26, 2012
That would be difficult and disruptive to remove at a later date. This option would also complicate a future extension of the line and or station. And abandoning the tbms in the ground object columbus would require the sfmta to compensate the contractor for the loss of resale value to machines, removing the tbm trailing gear, and also could cause some potential schedule delays to the existing tunnel contract and station work. Option 4 is removing the tunnel blowing machines at 17 31 powell stree...
Source: archive.org