Well we have: Union Pacific, B&O, CSX, Norfolk Southern, and AmTrak.
If you want to keep Union but make a parody you could use "Union Atlantic" showing it starting on the East coast and joined the Union to the west. You could use "Union BO" since Freeside is a dump and this is wasteland How much soap is there?!?!? "Union Trak" could be one, or if you like the Commonwealth reference but too long make it "Union CW13" for the Union of the 13 commonwealths, or Union A&P for Union Atlantic & Pacific showing that it goes coast to coast.
Hope some of these might help.
Keep up the amazing work Tricky. Can't wait to see the final.