Complex sentence: The line is distinguished as being more of a suburban railway; it is one of only two Underground lines to cross the Greater London boundary (the other being the Central line) and it is also the only Underground line with an express service at peak times.
Split into simpler sentences: The line is a suburban railway and one of only two Underground lines to cross the Greater London boundary (the other being the Central line). It is also the only Underground line with an express service at peak times.