That is the Union Pacific line between St. Louis and Poplar Bluff (and eventually Little Rock and Dallas) that was originally the St Louis and Iron Mountain, then Missouri Pacific. It is not as heavily used as it once was when the local iron, lead, and other mineral mines in the area were operating. It is the original route of the Texas Eagle on the MoPac and is still the route of Amtrak's Texas Eagle between St Louis and Dallas (the trains pass this point in the wee, dark hours of the morning).
looks like a rr runs under this bridge what rr is it?