The current doubleheading of trains 45 and 26 is indeed a recent phenomenon, I think it started happening last Monday (1/30). At first I thought it was just a random thing, but then after it started occurring several days in a row, I began to think this was going to be a regular deal... however long it lasts.
Before service to Elburn started, I recall the doubleheaders were regularly assigned to trains 55 and 32, although not every day. Why this was changed, I have no idea, perhaps Metra was bored with the current arrangement, perhaps they were testing out something else, maybe they were using a new dartboard... take your pick.
I had suspected that 56's turn to 61 was going to be a little tight at times, and at least a couple of days this week, 56 wound up downtown a little after 6pm, which caused UP commuter control to assign 54's equipment to 61, turning 61 into a six car train instead of its usual eight. The problem is that Proviso and Global 1 start churning out a fleet of westbound freight traffic between 1 and 4pm, trying to squeeze in as much traffic as possible before the rush hour curfew. Included among this daily westbound parade is a hot intermodal train called "The Bird", which usually has 3 SD70M's on the point, and on average, about 7 westbound freights travel the Geneva Sub during this three hour window.
Another frequent occurrence is that many eastbound freights that were being held at staging points like Elburn, LaFox, Wheaton, or Finley Rd. (Lombard) from earlier in the day due to capacity issues at Proviso usually get the green light to start moving again around this time of day (1-4pm) as well, so as you can see, the odds of delays to Metra traffic due to, you guessed it- "Freight train interference" increases exponentially.
And it just happened to be 37's (then 56's) misfortune to get nailed twice this week with delays due to the aforementioned "Freight train interference", causing that equipment to arrive OTC too late for its turn to 61. It is my opinion that 37/56 should be a six car set that always turns to 63, and change 35/54's equipment to an eight car set that always turns to 61. Plenty of recovery time available in both cases. But then again, we're just railfans, and AMTK84's comment about authority figures likely not knowing there's even a problem here probably isn't too far from the truth.
--Dorian--