High Quality Content by WIKIPEDIA articles! US Route 12 (US 12) is a state highway in north central Idaho. It extends 174.210 miles (280.364 km) from the Washington state line in Lewiston east to the Montana state line at Lolo Pass, generally along the route of the Lewis and Clark expedition, and is known as the Northwest Passage Scenic Byway US 12 enters Idaho at the Washington state line in Lewiston, Nez Perce County, crossing the Snake River at the state line. It heads east through Lewiston, turning north to cross the Clearwater River and intersect SH-128. It continues east to overlap US 95 along a limited access section. The overlapped highways run east along the north bank of the Clearwater River for 7.299 miles, leaving Lewiston and entering the Nez Perce Indian Reservation before separating.