Train movements through busy rail junctions were often controlled by operators housed in interlocking towers. The name refers to the interlocking nature of switches, locks, and signals. Typically, the opening or closing of the switch on one track would affect another switch, lock, or signal somewhere else at the junction.
The tower above, built in 1905, stood near Mitchell and Nelson streets in downtown Atlanta until 2018 when it was demolished. It was one of two such towers at the Atlanta Terminal Station complex, most of which was torn down in the early 1970s.