Withdrawn August 1, 1987
Length: 15.321 miles
Junction K-7 on Shawnee Mission Parkway in Shawnee (1984-1987)
Missouri State Line on Southwest Blvd, Kansas City (1984-1987)
Counties Passed through: Johnson, Wyandotte
Although the proposed K-12 was designated first, it was the last part of the Lawrence-Kansas City freeway to begin construction in 1980. Grading was completed by August of 1982 when work on the highway was suspended.
In December of 1983, KDOT switched the designations of K-10 and K-12 east of K-7. A year later, the new freeway between K-7 and I-435 was opened as K-10, and the original K-10 between K-7 and the Missouri line was officially re-designated as K-12
In 1983, only the westernmost 85 feet of K-12 was in rural Johnson County, with the remainder within the city limits of Shawnee, Merriam, and Kansas City. By 1987, Shawnee had annexed out past K-7. With the entire route urbanized, K-12 was turned back to the respective cities and removed from the State Highway system.