Complex sentence: In the 1970s to 1990s the infrastructure was updated, and the lines were partially relocated: they are now part of the Vienna U-Bahn services'U4' and'U6'.
Split into simpler sentences: In the 1970s to 1990s the infrastructure was updated, and the lines were partially relocated. It is now part of the Vienna U-Bahn services'U4' and'U6'.