[1] Five routes were introduced in the early 1950s: from outermost to innermost, the Red, Orange, Yellow, Green, and Blue Belts.

The Allegheny County Belt System was developed in the late 1940s by Joseph White, an engineer with the Allegheny County Department of Public Works, as a wayfarer system using a network of federal, state, and municipal roads to offer residents alternative traffic patterns that did not lead to downtown Pittsburgh's congested Golden Triangle.

The construction of the Interstate Highway System and regional parkways during the late 1950s through the early 1970s initially reduced the use and need of the belt routes.

As urbanization of the county spread further out from the City of Pittsburgh, however, the Belt System helped reduce suburban congestion.

Many of the roads selected in the mid-20th century today play key roles in the long-range regional transportation plans of Allegheny County.

Rick Sebak of WQED television also produced a local feature on the Allegheny County Belt System in the 1990s.

In the mid-1990s, the City of Pittsburgh developed a Purple Belt for the downtown area using the county system as a guideline.

Opponents of a full beltway have suggested residents should use the belt system, although some have said that the city doesn't promote it enough and wonder why signage for it is still maintained.

The Purple, Blue, and Yellow belts are complete loop routes, beginning and ending at the same points.

The current Red Belt is 33.5 miles (53.9 km) long[5] and runs through largely rural communities.

The Red Belt briefly enters Beaver County in two places where it crosses to the north bank of Big Sewickley Creek.

Both ends of the Red Belt originally ran outside of Allegheny County and were truncated to their current termini in 1974.

Western end: Began at the PA 51 end of the Ambridge-Aliquippa Bridge in Aliquippa/Beaver County, ran across the bridge (Ohio River) to 11th Street in Ambridge, right on Duss Avenue, right on 8th Street, left on PA 65 South into Allegheny County, and left on Cross Street in Leetsdale where the current Red Belt begins eastbound Eastern end: Began at the intersection of Leechburg and Freeport Roads at PA 366 in New Kensington/Westmoreland County and ran along PA 366 West, across the Tarentum Bridge (Allegheny River) into Allegheny County and continuing where the current Red Belt begins westbound The Orange Belt is longest belt in the system, running 91.7 miles (147.6 km).

Originally, the Orange and Yellow Belts were the only two in the system to cross all four major Allegheny County rivers.

The Yellow Belt stretches from its southernmost point in South Park, north and west to the border of Moon, north and east to Hampton and West Deer, and east as far as the border to Penn Hills/Plum before returning to the start.

Curry Hollow was a former town along this road, where it crosses the CSX railroad tracks next to Jefferson Memorial Park.

[1] (The gap is due to geographic concerns rather than intersecting with other counties, as is the case with the Red and Orange Belts.)

The Blue Belt crosses the Ohio River via McKees Rocks Bridge between McKees Rocks and the Brighton Heights neighborhood of Pittsburgh, Allegheny River via Highland Park Bridge between Sharpsburg and the Highland Park neighborhood of Pittsburgh, and Monongahela River via Homestead Grays Bridge between the Pittsburgh neighborhood of Squirrel Hill and Homestead.

[citation needed] For one mile in northeastern Pittsburgh, the Blue and Green Belts form the only concurrent segment in the system.

The two belts meet (Blue northbound, Green southbound) at the northern end of the Highland Park Bridge off Exit 6 on PA 28.