Missouri also maintains a secondary set of roads, supplemental routes, which are lettered rather than numbered.

In some states (such as Arkansas and New Mexico), highways are allowed to be discontinuous.

Missouri overlaps highways in order to maintain continuity.

The Missouri Department of Transportation routinely uses the term "Route" in reference to the names of the roads.

Missourians may use the terms "Route" and "Highway" interchangeably when referring to a state road.