Complex sentence: The Great Western main line opened in 1838, serving a temporary terminus the other side of Bishop's Road and when the current Paddington station opened in 1854, the line passed to the south of the old station.
Split into simpler sentences: The Great Western main line opened in 1838, serving a temporary terminus the other side of Bishop's Road. When the current Paddington station opened in 1854, the line passed to the south of the old station.