In road transportation in the United States, a special route is a road in a numbered highway system that diverts a specific segment of related traffic away from another road. They are featured in many highway systems; most are found in the Interstate Highway System, U.S. highway system, and several state highway systems. Each type of special route possesses generally defined characteristics and has a defined relationship with its parent route. Typically, special routes share a route number with a dominant route, often referred as the "parent" or "mainline", and are given either a descriptor which may be used either before or after the route name, such as Alternate or Business, or a letter suffix that is attached to the route number. For example, an alternate route of U.S. Route 1 may be called "Alternate U.S. Route 1", "U.S. Route 1 Alternate", or "U.S. Route 1A". Occasionally, a special route will have both a descriptor and a suffix, such as U.S. Route 1A Business.

The United States Numbered Highway System is an integrated network of roads and highways numbered within a nationwide grid in the contiguous United States. As the designation and numbering of these highways were coordinated among the states, they are sometimes called Federal Highways, but the roadways were built and have always been maintained by state or local governments since their initial designation in 1926.