Near Smithton in Pettis County, there's an unusual little highway: Spur US 50. Most Missouri spur routes are from state highways. Spur US 50 is also concurrent with supplemental Route W until the highway reaches the Smithton city line on the north side of town. Then Route W bypasses the town on an old alignment of US 50 while Spur US 50 goes through the town. Spur US 50 ends on the east side of Smithton at the city line.