In 1952, the Milwaukee Road enjoyed a Net Revenue of $47M, basking in the the glow of a postwar boom in economic activity . This was the era of the Little Joe and a time of prosperity for the rail industry as a whole. But hidden in the glow of the era was this note, "Revenue passenger miles showed a decrease of 5% (over the prior year)," with total passenger income of $18.8M .
In 1952 the entire passenger train market in the United States was changing. New pressures were coming to bear on the industry that included more accessible air travel, the expansion of automobiles and the interstate highway system. Passenger train profit, following a wartime peak, would begin a precipitous decline that culminated in the formation of Amtrak in 1971. In 1961, the Milwaukee would pull its own transcontinental Olympian Hiawatha. The company gave it the following epitaph it is 1961 Annual Report :
The Interstate Commerce Commission approved the discontinuance of Olympian Hiawatha passenger trains between Deer Lodge, Mont., and Seattle-Tacoma, Wash., resulting in an annual saving of 485,450 train miles and estimated net annual dollar savings of $1,715,000. 
No longer viewed as assets, passenger trains had become liabilities in a sea of growing expenses and carrying costs.
In 1952, however, the railroad received a new type of dome car from Pullman-Standard. Known on the Milwaukee Road as a "Super Dome," the car represented an engineering feat. It was designed to be self contained with diesel-powered generators and a/c equipment. The lower level was complete with a small bar area while the upper level boasted a Solex-glass equipped dome that stretched the entire length of the car . The image below is courtesy of Michael Hicks and Wikimedia.
Each car represented a significant investment by the Milwaukee, but also a final attempt to win back passengers to a slipping segment of the industry. Despite the effort, the Super Domes plied the rails to the coast for less than a decade before being pulled back in 1961.
Although other railroads adopted full length dome designs, the Super Domes ran under wire. They were pulled by the Rocky Mountain Division's best: steam boiler equipped Little Joes. The Super Domes in Olympian Hiawatha Service offered what must have been spectacular views. The wheat fields of the Dakotas, the Badlands of East Montana, the crossing of 5 mountain ranges, and the final crossing of the Missouri River at Lombard, MT.
The crossing of the Missouri River at Lombard is seen above, the Milwaukee Road grade and bridge are still distinct against the backdrop of Montana mountains. These were views well suited for the Super Dome, and apart from the missing bridge section, it's easy to imagine the orange and red Olympian Hiawatha slipping out of the confines of 16 mile canyon, over the NP below, and out across the Missouri headwaters even now.
Lombard, MT: 1430.4 Miles from Chicago.
Note: The author thanks Michael Sol and the Milwaukee Road Archives for posting material referenced in this article.
1) Milwaukee Road, 1952 Annual Report
2) Milwaukee Road, 1961 Annual Report
3) Milwaukee road’s super dome cars. Railway Age, pages 68–74, 1952.