Complex sentence: They also operate mostly on the Northern, Caulfield and Sandringham group lines although still able to run on the Burnley and Clifton Hill group but most of the time they do not operate at all due to high proportion of newer X' Trapolis trains on those lines.
Split into simpler sentences: They also operate mostly on the Northern, Caulfield and Sandringham group lines, although they are still able to run on the Burnley and Clifton Hill group lines. But most of the times they do not operate at all due to high proportion of newer X' Trapolis trains on those lines.