It seems to me the Union Pacific was able to play the Iowa roads (Chicago & North Western, Great Western, Rock Island) against each other to their advantage. Here we see three trains of the Union Pacific racing across the double-track mainline of the C&NW near Denison. (The trains here in order: EB east of Vail, EB at Denison, EB west of Carroll, and WB east of Vail.)
The final image seems to be all C&NW—perhaps this is their hot train that ran between Chicago and Fremont. Now that I think of it, perhaps all of these would interchange with the UP at Fremont, rather than at Omaha. All lead locomotives are EMD SD40-2s.
I posted two of these before—albeit the black and white versions. One will note that the C&NW was known for running their trains on the “wrong main”. But for this railroad, left-hand running was “right”. That bell placement on the nose is distinctive as well.
Four images by Richard Koenig; taken December 22nd 1976.