The Belt System was not intended as high speed or limited access roads, but instead their purpose was to define a road system way from the major arteries and the congestion that they suffered.  The colors of the system are ordered like the colors in a rainbow with the outermost red, followed by orange, yellow, green, blue, and purple.  So if you cross one color, you have an idea of how close you are to downtown and whether you are heading towards or away from the central business district.  

The Interstate Highway construction and Parkway construction from the late 1950s though the early 1970s reduced the use and need of the Belt System.  However, as urban sprawl got a hold of Pittsburgh, the system helped to reduce the effects of suburban congestion.  Many of the roads selected more than fifty years ago, still play a key role in the transportation plans for Allegheny County.  Many of them that were chosen for the belts have gone from country lanes to urban collectors to urban arterials.

In 1966, the belt took its current form between Truck US 19 and US 19 in Dormont.  Prior to that year, it followed Potomac Avenue, Dwight Avenue, and US 19 back to the intersection with Potomac.

In 1973, the route was moved from Kleber Street, Brighton Road, and Jacks Run Road to its current alignment between Benton Avenue and Bascom Street in Bellevue.  It was moved from Seavey Road, Parker Street, Butler Street, Bridge Street, and PA 8 between Evergreen Road and the Highland Park Bridge to its current alignment.  It was moved from Frankstown Road and Dallas Avenue to Fifth Avenue and Beechwood Boulevard between East Liberty and Squirrel Hill.

In 1974, the route was moved from Beechwood Boulevard onto the current alignment from Fifth Avenue to Browns Hill Road.  Signage was removed from PA 885, Glass Run Road, Churchview Avenue, Brownsville Road, and Maytide Street and placed on its current alignment between the Glenwood Bridge and Maytide Street.  In McKees Rocks, it was moved from Singer Avenue, Valley Street, Broadway, Seventh Street, and McCoy Road to the current alignment between Chartiers Avenue and PA 51.

In 1992, a leg of the belt which was signed on Shady Avenue and Monitor Street between Forward Avenue and Beechwood Boulevard was decommissioned.

In 2002, it became the first belt to be signed on an Interstate when it was moved from PA 51, Sewickley Bridge, PA 65, Kilbuck Street, and Glenfield Road to PA 51, Ferree Street, Neville Island Bridge, Grand Avenue, and I-79 between PA 51 and Mount Nebo Road.