Complex sentence: Continuous welded rail (CWR) mostly relies on heavy sleepers and ballast to constrain any expansion or contraction, but expansion joints are installed on steel bridges where the bridge itself has its own expansion joints.
Split into simpler sentences: Continuous welded rail (CWR) mostly relies on heavy sleepers and ballast to constrain any expansion or contraction. Expansion joint would be installed on steel bridges where the bridge itself has its own expansion joints.