Complex sentence: The railway is below ground in the central section and on the loop east of Paddingdon, and, unlike London's deep-level tube railways, the railway tunnels are just below the surface and of similar size to those on British main lines.
Split into simpler sentences: The railway is below ground in the central section and on the loop east of Paddingdon. Unlike London's deep-level tube railways, the railway tunnels are just below the surface and of similar size to those on British main lines.