My mistake....Tunnel 11.
Whether or not the rail you photographed was the main, or a house track, depends on the weight. If it's 132 pound/yd steel, this was probably from the main line (or maybe 131 pound/yd, which was a popular rail section used by the Southern back then). A house track would have been 100 pounds, or maybe even 70.
I think this was the old main line. And---given the year the steel was rolled (1925), that rail carried Ps-4 Pacifics, Ms-4 Mikes, and the original FT demonstrator, EMD 103, in 1939.
Lots of history there...