The shift to one person RTO's started in earnest when the Orange line opened for business in 1993. Within two years, the Brown line was assimilated into the procedure, then the newly rebuilt Green line followed suit as well when it re-opened in 1996 after a two year shutdown. The Red, Blue, and Purple (Evanston) Express lines were the last holdouts, and in Chicago transit history, the date of November 8, 1997 is the final day that traditional conductors were used on CTA. As Mike indicates, 1999 was indeed the last year that "subway only" conductors were used on the Red and Blue lines, although I don't remember the exact date that practice ended...
--Dorian--