Complex sentence: Berlin and Hamburg planned the expansion of their existing U-Bahn networks, while the majority of the Western German cities decided to upgrade their tramway networks step by step, linking new'second level' infrastructure to existing sections.
Split into simpler sentences: Berlin and Hamburg planned the expansion of their existing U-Bahn networks. However, the majority of the Western German cities decided to upgrade their tramway networks step by step, linking new'second level' infrastructure to existing sections.