Station update: cool machines

They are finishing up the new tracks at Union Station.  Laying track is interesting--first a deep trench, then rock ballast;  the ties (sleepers in the UK) are adjusted first by hand with long poles and a tape measure,  and then the long rails are welded together to create continuous rail.  Finally,  these wild machines run along and dig in and push rock around.  Maybe a railfan will tell us what they are doing.