Complex sentence: Upon duplication of the main line safeworking was provided by Tyers 3 wire block instruments, these were latter replaced by Tyers 1 wire, 3 position instruments, the Stanford branch was worked by electric staff from Aberdare Junction.
Split into simpler sentences: Upon duplication of the main line safeworking was provided by Tyers 3 wire block instruments, which were later replaced by Tyers 1 wire, 3 position instruments. The Stanford branch was worked by electric staff from Aberdare Junction.