Complex sentence: Dan Ryan Line was a rail rapid transit route once operated by the Chicago Transit Authority (CTA) from September 28,1969 to February 21,1993 uniting two transit corridors that until 1969 never had through rail service.
Split into simpler sentences: Dan Ryan Line was a rail rapid transit route formerly operated by the Chicago Transit Authority (CTA). When initially created, the route united two transit corridors that until 1969 never had through rail service.