Complex sentence: The first of these, the Rome-Lido railway line, which connects Rome to the sea at Ostia, is effectively part of the metro network, is run along similar lines and using trains similar to those in service on the A and B lines.
Split into simpler sentences: The first of these, the Rome-Lido railway line, which connects Rome to the sea at Ostia, is effectively part of the metro network. It is run along similar lines to the metro and uses trains similar to those in service on the A and B lines.