Complex sentence: Those identities became "fallen flags" when the group was renamed Seaboard System Railroad (SBD), and in 1986 SBD merged with Chessie System to form CSX Transportation.
Split into simpler sentences: Those identities became "fallen flags" when the group was renamed Seaboard System Railroad (SBD). In 1986 SBD merged with Chessie System to form CSX Transportation.