This bridge is currently over both the CSX and Norfolk-Southern mains. Historically it was even more confusing.
As well as through trains, the Southern Railroad (now Norfolk-Southern RR) ran to Terminal Station where they met the Central of Georgia (now NS) and the Atlanta and West Point (now CSX). The Seaboard (now CSX) had trackage rights on the Southern track from Howell Wye to Terminal Station.
The NC&StL with (and who later merged with) the L&N (both now CSX) along with with the AB&A (later AB&C, later yet Atlantic Coast Lines, all now CSX) originally passed here to Union Terminal where they met the Georgia Railroad (now CSX) coming in from the East. To confuse things further, the Seaboard also had trackage rights on the Georgia Railroad to bypass Atlanta from the East and proceed through to Terminal Station.
Approach this bridge with caution! This is Atlanta's Hooverville. Homeless residents can be aggressive!