Fire in the Sky
From Max Lowenthal's Personal notes of the ICC hearings, July 6-7 1927. Walter Colpitts is the senior author of the Coverdale and Colpitts study. 
"It will be disastrous to the Lines East if the Puget Sound were separated. [There are] possible connections for the Puget Sound [to receive and deliver traffic] ... [but there are] no likely connections for the Lines East." [Vol 2, page 292, Colpitts testimony, Lowenthal notes].
Milwaukee Road's chief financial officer, W.W.K. Sparrow, had independently analyzed the question. "Any breakup in the St. Paul system would be very bad for both east and west" [although] "there are several lines with which the Puget Sound Lines could make connections ..." and do good business.
Well before the benefits of Burlington Northern merger concessions added to Milwaukee's ability to 'receive and deliver traffic,' the idea of splitting off a Midwestern 'core' railroad was considered .... and called disastrous.
The opening of those gateways in the Northwest as a result of that merger did indeed show significant results. The Milwaukee Road of the early 70s was able to claim almost 80% of traffic out of the Port of Seattle and almost 50% of Northwest container traffic . Fast forward to 1980: the arguments of 1927 are cast aside and the improved positioning of 1970 are lost in a sea of hard winters, derelict locomotives, and a vision that looks only at the Midwest. In 1980, it was deemed necessary and prosperous to walk away from Lines West. The fallout, however, was disastrous just as Walter Colpitts had predicted 50 years prior. The new corporation (Milwaukee II) immediately lost more money than it ever had with Lines West in operation .
In the photo above, the sun drops below the Rocky Mountains at the end of another day on Lines West, leaving behind it nothing but dark and quiet - and time to consider what happened.
1) Files and materials available: milwaukeeroadarchives.com/Bankruptcy
2) Jones, T. "What Really Happened" http://www.trainweb.org/milwaukee/article.html