US 166 and US 400 have a brief run in Missouri before the routes end at Exit 1 of I-44 in Newton County. Kansas and Oklahoma both are not far away from this location.
Note how Missouri had been dealing with the need to use three digits for a route number on a standard-size shield. The numbers for 166 are crowded in, which is doable because 1 is a narrow-width character, while the numbers for 400 are in a smaller font than that usually used for Missouri highway signs. In 2000, Missouri started using wider, rectangular markers for three-digit US and numbered state highways, as well as for two-letter supplemental routes.
The end of the route is about a mile from this location.
Photo courtesy of Mark Stauter