SR 128 begins at Jct US 12 just west of Clarkston, heads north across the Snake River on the Red Wolf Crossing (bridge) to Jct SR 193, then east to the Idaho state line where WA SR 128 ends. SR 128 is 2.30 miles long. Idaho SR 128 begins at the end of WA SR 128 and continues east to Jct US 12 in North Lewiston.
When first posted as such in 1964, WA SR 128 started at Jct US 12 in Pomeroy, headed south, then east via Peola, returning to US 12 just west of Clarkston. The extension of WA SR 128 to the Idaho state line and the designation of ID SR 128 occurred in 1990. Effective April 1, 1992, the original portion of SR 128 from Pomeroy to Clarkston was dropped from the state highway system.
Before 1964, the Pomeroy to Clarkston portion of SR 128 had been SSH 3K.
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