Complex sentence: The following years saw changes to the Red Arrow route network, in June 1969 a minor adjustment to 505, and the addition of the 508; in the summer of 1969 route 509 replaced 508 and in 1970 route 513 was added.
Split into simpler sentences: The following years saw changes to the Red Arrow route network, in June 1969 a minor adjustment to 505, and the addition of the 508. In the summer of 1969 route 509 replaced 508 and in 1970 route 513 was added.