Complex sentence: There was once a plan to use the Nanbu Jūkan to connect Tohoku Shinkansen with Noheji or Mutsu, but the railway was closed before the construction of Tohoku Shinkansen started.
Split into simpler sentences: There was once a plan to use Nambujuukan to connect Tohoku Shinkansen with Noheji or Mutsu. But Nambujuukan Railway was closed before the construction of Tohoku Shinkansen started.