Missouri’s Supplemental State Highways form one of the most distinctive secondary road networks in the country. Unlike the numbered state highways that traverse long distances and major corridors, these supplemental routes are designated with letters—sometimes single, sometimes double—and serve primarily rural areas. Managed by the Missouri Department of Transportation (MoDOT), these roads ensure that even the most remote parts of the state maintain essential links to the broader highway system.

The system was introduced in the 1950s as part of an ambitious effort to provide all-weather access to farms, schools, and markets. Today, Missouri’s lettered routes—such as Route A, Route BB, or Route Z—are a lifeline for small towns and agricultural regions. They range in quality from modern two-lane roads to narrow, winding paths that follow older alignments or natural terrain. Many supplemental routes connect to larger highways, enabling smoother transitions between local and regional travel.

What makes Missouri’s Supplemental State Highways especially notable is their scale and clarity. No other state uses this kind of letter-based system so extensively. These routes are typically shorter in length, but collectively they represent thousands of miles of infrastructure that support everyday life in rural Missouri. Whether you’re navigating through the Ozarks or crossing flat farmland in the north, you’re likely to encounter these uniquely labeled roads.