Embedded Files
100 years of US routes: 1926-2026
Endpoints of
1959-1962
East: Detroit, MI
West: Missoula, MT
1962-1967
East: Detroit, MI
West: Lewiston, ID
1967-present
East: Detroit, MI
West: Aberdeen, WA
Mileage: in 1989 AASHTO listed a figure of 2491 miles for US 12... however, that included the mileage of US 12's associated business routes. According to the state subtotals on AASHTO's 1989 spreadsheet, mainline US 12's actual end-to-end total at the time was 2483 miles. That closely matches our own 2020 measurement, which yielded 2477.7 miles. In North Dakota, US 12 passes through only the far southwest corner, less than 100 miles. Despite that, US 12's midway point happens to fall in Bowman ND. Want historic mileages? Our handy reference book includes the mileages that were published in all 13 of AASHO/AASHTO's historic route logs (spanning the years 1927 to 1989).
The east end of US 12 has always been in Detroit (although its exact endpoint there has changed a bit over the years). US 12 has not always gone all the way to the Pacific Coast; its west end was originally in Miles City. In 1938, the US 12 designation was extended to Silver Gate, at the northeast entrance to Yellowstone National Park (maps and more info on the US 312 page). From Forsyth MT, it was overlapped with US 10 (roughly along today's I-90) through Billings. At Laurel, US 12 split off to follow the route which today is designated US 212: through Red Lodge, over Beartooth Pass, through Cooke City/Silver Gate, into Yellowstone. That was the case until 1959. That year, US 12 broke off from US 10 at Forsyth to follow its present route through Helena; it ended in Missoula at US 93:
c. 1960, Gousha
Missoula
At the time, US 93 came in from the south on Higgins Avenue and left town via Broadway. This photo was looking west on Broadway:
Field/Kalina/Nitzman, Sep. 2006
Today that is westbound Business 12 / Business I-90, and the two routes separate there. Historically, northbound US 93 was ahead, and southbound was to the left on Higgins, so US 12 came west to that point and ended there. Then, in 1963, US 12 was extended west again: this time over Lolo Pass into Idaho, roughly along Lewis and Clark's historic trail, to Lewiston. Where it ended, US 410 began. But that situation lasted only four years: US 410 was decommissioned in 1967, and the US 12 designation was extended west for the last time: to Aberdeen, mostly along 410's former route, except for the segment between Naches and Elma WA.
Research and/or image credits: Chris Bessert; Mark Bozanich; Andy Field; Chris Kalina; Robert Mortell; Alex Nitzman; Dale Sanderson; Michael Summa; Mike Wiley
Page originally created 2000;last updated Aug. 13, 2025.
Page updated
Google Sites
Report abuse