A supplemental route is a state secondary road in the U.S. state of Missouri, designated with letters. Supplemental routes were various roads within the state which the Missouri Department of Transportation was given in 1952 to maintain in addition to the regular routes, though lettered routes had been in use from at least 1932. The four types of roads designated as Routes are: Farm to market roads Roads to state parks Former alignments of U.S. or state highways Short routes connecting state highways from other states to routes in Missouri Supplemental routes make up (59%) of the state highway system. History Prior to 1907, all road improvement activities in Missouri were undertaken by the individual counties, with little expertise or coordination between them. Amid growing automobile presence and insufficient road networks in Missouri in the ensuing years, the state legislature created a state highway department and the state highway commission as well as enacted various laws aimed at improving transportation in the state. In 1920, recognizing that economic prosperity and growth are highly related to good transportation, the legislature passed a $60 million bond issue for road work. This effort, along with the Centennial Road Law passed by the legislature in 1921, shifted highway building efforts in Missouri from the local level to the state level. As a result, the state highway commission undertook an aggressive road building campaign throughout the 1920s and 1930s aimed to get Missouri "out of the mud". In 1952, the state highway department embarked on its Missouri 10-Year Highway Modernization and Expansion Program. Through this effort, the state assumed maintenance responsibility of over an additional of secondary and farm-to-market roads previously managed by the counties. The goal of the secondary highway system was to place state-maintained roads within of more than 95% of all rural farm houses, schools, churches, cemeteries and stores. Most of Missouri's lettered supplemental highways are the result of this program. Highway designations The more major supplemental routes of the system are assigned single-letter designations (such as "K"). Minor branch routes and farm-to-market roads, which often end at county roads or are former alignments of the other highways, are typically assigned two-letter designations consisting of two of the same letter (e.g. "KK"). Additionally, combinations of letters may be used, but always with A as the first letter (such as "AD"); the only exceptions to this are Route BA in western St. Louis