High Quality Content by WIKIPEDIA articles! U.S. Route 12 (US 12) is a major east-west U.S. Highway, running from Aberdeen, Washington, to Detroit, Michigan. It spans 403.80 miles (649.85 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.