An official alternate route
is an auxiliary route
that provides an alternate alignment for a highway. Originally, the term for these routes was "optional"; but in 1959, the designation became alternate. In some cases, a business route
exists and a third such alignment is needed (this was the case with former Alternate US 71
which bypassed Joplin, Missouri
). Alternatively, a town (or towns) desired to be on the particular highway, which was routed differently to put an important town or city on the route. In Oklahoma
, U.S. Highway 412
has an alternate route where the main highway is routed down the Cherokee Turnpike
; this route has been designated Scenic US 412
, though it is shown as "Alternate US 412" on some maps.
In at least one case, the banner "Optional Route" was retained when a second alternate route existed. This happened in Kansas City, Missouri with U.S. Route 40 which had an alternate and an optional route simulataneously.
In some states, an alternate route will be designated by adding an "A" after the number instead of a sign marked "Alternate" above it. Example: "US 69A" means "Alternate US 69".