Modeler's Moment - It's not always the mainline that is higher

Mainline and siding tracks at different elevationsSo we're always told as model railroaders that the mainline is always at a higher elevation than the sidings.  We should also be told that once someone says that something never happens on the prototype, someone else will come up with a photo to prove him wrong.  The latter principle was proved again today as I found this mainline and siding pair in Madison, Wisconsin, today.  The mainline, on the right in this photo, is at a slightly lower elevation than the siding, at the left.  The wear pattern in the switch frog at the bottom of the image confirms which alignment is the mainline here; the shiny rails are clearly the rails on the rightmost track.  The question then falls to why it is this way at this location.  Well, the area to the right where the Kohl Center is now located, used to be part of the Milwaukee Road's main switch yard in Madison, so it stands to reason that the mainline bypass around the yard used to be the track on the left.