On a trip to Springfield, Illinois on 26 April 1992, I ran across Avenue Tower quite by accident, while driving around the town.
There was no operator on duty, but I did manage to photograph the tower together with Illinois Central, a GP38-2 built for the Illinois Central Gulf in 1974.
Avenue Tower was at one time a complicated interlocking, guarding the crossing of the Chicago & Illinois Midland, the Gulf, Mobile & Ohio, Baltimore & Ohio, and Illinois Central. By this time many of the tracks had been pulled, and the tower was no longer open 24 hours a day. The tower closed on 12 November 1992, and the building was demolished in May 1993.