WHY THE DIESELS PREVAILED.

The Mid-Week, a local newspaper, includes vintage photographs in its Looking Back column.  The November 2 edition included a Chicago and North Western mail train, probably a local, taking coal at the DeKalb coal chute in 1955 (the same one that still straddles the track near the airport.)

 Mid-Week photograph from Joiner History Room collection.

I'm not familiar enough with C&NW locomotive assignments to say that the power, Pacific 644, is from the Chicago commuter pool, which is the most likely place to find steam locomotives in those days.  The iron horse, for all its smoky glory, had to be fed and watered much more frequently than the diesels.  There's a little more time to sort the mail before the next sack has to be kicked off, but there's likely at least one passenger fretting over the delay.