U.S. Route 89 in Utah partially coincident with U.S. Route 91 in Utah
History
When US-89 was created in 1926, it only went as far north as Spanish Fork, where travelers could continue to Salt Lake City via US-91. The highway was extended north to the Canada–US border near Glacier National Park in the mid-1930s, though a dispute between Utah and Idaho on the one side and Wyoming on the other was not settled until 1938. The American Association of State Highway Officials decided in favor of Utah and Idaho, placing US-89 on or near US-91 between Spanish Fork and Logan, where it split northeasterly to Yellowstone National Park. (US-89 only left US-91 twice: between Farmington and Ogden, where it still travels today, and via an all-weather route from Brigham City into the Cache Valley, now SR-38 and SR-30.) Wyoming's preferred routing, which left US-91 at Provo, instead became US-189. Beginning in the 1950s, Interstate 15 was constructed, replacing US-91 for through traffic south of Brigham City, and leading to that route's truncation there in 1974. On the other hand, US-89 follows independent corridors south of Spanish Fork and north of Logan. It has not been truncated and mostly follows US-91's final alignment, except between Farmington and Ogden (where old US-91 is now I-15, SR-126, and SR-26).
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