Complex sentence: The line from Abercynon-Merthyr Tydfil is now a single line operation, the dual track being removed in the early 1970s, although some dual track has since been brought back at Merthyr Vale running towards Merthyr Tydfil to help with the increased frequency of services.
Split into simpler sentences: The line from Abercynon-Merthyr Tydfil is now a single line operation, the dual track being removed in the early 1970s. Nb Some dual track has since been brought back at Merthyr Vale running towards Merthyr Tydfil to help with the increased frequency of services.