US 12 Trunk
US 12 was extended west into Washington State from Lewiston, Idaho to Aberdeen, Washington in 1967. US 12 had been extended west from Missoula, Montana to Lewiston in 1963 after paving of the highway over Lolo Pass was completed in 1962.
US 12 follows the basic route of former US 410 from Aberdeen to Elma and from the Naches area to Lewiston. From Elma to Grand Mound, US 12 follows what had been numbered SR 8 from 1964 to 1967. US 12 runs coincident with I-5 from Grand Mound to the vicinity of Marys Corner.From Jct I-5 near Marys Corner to Naches, US 12 crosses White Pass along what had been numbered SR 14 from 1964 to 1966. Former US 410, now SR 410, crosses Chinook Pass, closed in winter. The Washington State portion of US 12 is 430.81 miles long.
Business US 12 Walla Walla
When the US 12 bypass at Walla Walla opened to traffic around 1973, former US 12 through town became Business US 12. Over time, Business US 12 signs were removed from the exits at either end of town but as of Summer 2002 were still posted along the business route through town.
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