Special route
[citation needed][2][3] The term is not all-encompassing however, as not all special routes have these sign plates.
As of 2009, the standards organization only advocates four types of special routes: business, bypass, alternate, and temporary.
These older alignments may be given street names like "Old U.S. Highway 52", or in some rare cases, be signed with route shields attached to "Old" or "Historic" sign plates (such as decommissioned sections of former U.S. Route 66 that are still driveable).
[6] They sport green Interstate shields, as opposed to the normal red and blue, with the word "Business" replacing the normal "Interstate" word on the upper portion of the shield.
Truck routes were initially known as Bypass routes, and were loops created as a means to divert through truck traffic away from population centers, but the designation was changed to "bypass" in 1959-1960 by AASHTO.
Today, Truck routes exist as alternatives for the mainline routes that are ill-suited for large truck travel[7] with obstacles (such as low clearance bridges, sharp turns, or steep grades) or with conditions that could create dangerous situations to smaller vehicles.
They are mainly routed on major highways and freeways and other roads they intersect to bypass that specific bridge.
Both Spurs and Connectors are generally very short in length, not spanning more than ten miles (16 km).
Temporary routes generally traverse along roads of a lower standard than the planned mainline.
This will obviate much hard feeling when it is necessary to change a number to the permanently established route.
[5] A rare type of special route, known as the Emergency Detour route, is signed with an auxiliary "Emergency" banner that is colored orange, indicating a temporary traffic control sign.
The purpose of these routes is to offer an alternative in case the parent route is impassable, due to either a traffic jams, traffic collision, or road closure (for a variety of reasons).
According to the Michigan Department of Transportation, "This route would only be used in emergency situations and worst-case scenarios impacting the entire bridge structure.
[11] Ontario, Canada is one jurisdiction outside the United States with a very prevalent system of these roads.
These splits were in the system of United States Numbered Highways from the beginning, and were used when two roughly equivalent routes existed.
They are usually loops, but some have been spurs, though since they use directional letter suffixes, they are not generally considered "bannered routes".
Originally in the United States, the terms used for special routes were "City", "Truck", and "Optional".
The American Association of State Highway and Transportation Officials (AASHTO) has called for the removal of "alternate" routes, though many still exist.
