Unlike many major American cities that utilize number-coded limited-access roads to form belt systems, the belts in the Allegheny County Belt System are not intended to be used as high-speed routes. Rather, the belt system is to be used as a navigational aid for motorists in unfamiliar portions of the county. Roads that make up the Belt System retain their previous names. The five original routes are, from outermost to innermost, the Red, Orange, Yellow, Green, and Blue Belts. The Purple Belt was not part of the original system and was added later.