Complex sentence: This railway was planned to only last for one year, but it was kept and renamed "Pioniereisenbahn" in 1951 and the track was extended to running from Zoo over Carolasee and Palaisteich back to Zoo.
Split into simpler sentences: This railway was planned to only last for one year, but it was kept and renamed "Pioniereisenbahn" in 1951. At the same time the track was extended to running from Zoo over Carolasee and Palaisteich back to Zoo.