Complex sentence: Construction of the cut-and-cover route, only the fourth such in Great Britain, was formidably complex, but the line opened in 1886; it was steam operated, leading to complaints about smoky conditions.
Split into simpler sentences: Construction of the cut-and-cover route, only the fourth such in Great Britain, was formidably complex, but the line opened in 1886. It was steam operated, leading to complaints about smoky conditions.