 U.S. Route 12 ( US 12 ) is a major east @-@ west U.S. Highway , running from Aberdeen , Washington , to Detroit , Michigan . It spans 430 @.@ 80 miles ( 693 @.@ 31 km ) across the state of Washington , and is the only numbered highway to span the entire state from west to east , starting near the Pacific Ocean , and crossing the Idaho state line near Clarkston . It crosses the Cascade Range over White Pass , south of Mount Rainier National Park . Portions of it are concurrent with Interstate 5 ( I @-@ 5 ) and Interstate 82 ( I @-@ 82 ) , although the majority of the route does not parallel any Interstate Highway . 
