Complex sentence: Horseshoe Curve is a famous railroad curve in central Pennsylvania in the United States, built by the Pennsylvania Railroad and later used by the Penn Central, Conrail and most recently Norfolk Southern.
Split into simpler sentences: Horseshoe Curve is a famous railroad curve in central Pennsylvania in the United States (it is a Horseshoe curve). It was built by the Pennsylvania Railroad and later used by the Penn Central, Conrail and most recently Norfolk Southern.