PA 48 begins at an intersection with PA 51 in Forward Township, heading northeast on two-lane undivided Scenery Drive. PA 48 is concurrent with the Orange Belt of the Allegheny County belt system at this point, with which it remains concurrent with for the entire length. The route immediately turns to the north-northwest and forms the border between Forward Township to the west and Elizabeth Township to the east, passing through a mix of fields and woods with some homes. The road fully enters Elizabeth Township and curves north-northeast. At an intersection with Weigles Hill Road east of Elizabeth Forward High School, PA 48 makes a turn to the east, passing residences and turning to the northwest. The road passes through more areas of housing and woods, curving northeast as it passes more residential areas. The route makes a bend northeast prior to turning north at the Simpson Howell Road intersection and running past a mix of homes and businesses. PA 48 winds north through more areas of woodland and development, with the name becoming Boston Hollow Road at the Lovedale Road junction. Farther north, the road becomes the border between the borough of Lincoln to the west and Elizabeth Township to the east as it heads through more forested areas with a few homes. The route fully enters Elizabeth Township again and heads into commercial areas as it comes to the community of Boston, crossing the Youghiogheny River on the Boston Bridge.^[1][2]

At this point, PA 48 heads northwest into the borough of Versailles, passing over CSX's Keystone Subdivision railroad line and becoming Walnut Street as it passes a mix of homes and businesses. The route crosses into the city of McKeesport and widens into a divided highway as it comes to an intersection with PA 148. Here, PA 148 continues along Walnut Street and PA 48 turns east onto four-lane undivided Long Run Road, passing through more residential and commercial areas. The road curves south by more businesses prior to curving east past a mix of woods and commercial development, briefly entering Versailles again before crossing back into McKeesport. The route curves north before heading northeast and entering the borough of White Oak. Upon crossing Lincoln Way, PA 48 becomes Jacks Run Road and narrows to two lanes, entering more forested areas with occasional homes and businesses. The road continues north and heads into North Versailles Township and passes through more wooded areas of development, passing east of East Allegheny High School and turning northeast before coming to an intersection with US 30.^[1][2]

Past this junction, the route becomes Mosside Boulevard and runs past businesses prior to heading into forested areas. The road briefly passes through the borough of Wall prior to crossing back into North Versailles Township and heading into commercial areas, turning northeast. The route widens into a four-lane divided highway and passes over Norfolk Southern's Pittsburgh Line and Turtle Creek, entering the borough of Monroeville. Here, PA 48 becomes an undivided road as it comes to an intersection with PA 130. Following this, the road narrows to two lanes and passes through woods, curving more to the north. Farther north, the route enters commercial areas, widening into a four-lane road at the Haymaker Road intersection, where it passes between Gateway High School to the west and Forbes Hospital to the east. PA 48 turns northwest, passing more businesses and reaching its northern terminus at an intersection with US 22 Bus. near an interchange that has access to I-376/US 22 and I-76 (Pennsylvania Turnpike).^[1][2]

In 1963, a new PA 48 expressway was proposed to run parallel to the current PA 48 alignment from PA 51 in Elizabeth to the PA Turnpike/Parkway East Interchange in Monroeville. Although several houses and an amusement complex of swimming pool, amusement park and drive-in theater (called Rainbow Gardens) were demolished in the process, the project was scrapped by the 1970s. The route of the proposed highway is now followed roughly by the Mon–Fayette Expressway (PA 43).^[3]

The entire route is in Allegheny County.

Pennsylvania Route 48 Truck (PA 48 Truck) is a truck route of PA 48 that bypasses a weight-restricted bridge over a branch of Wylie Run in Lincoln, on which trucks over 32 tons are prohibited. The route follows PA 51, McKeesport Road, Lincoln Boulevard, Glassport-Elizabeth Road, the Clairton-Glassport Bridge over the Monongahela River, PA 837, the McKeesport-Duquesne Bridge over the Monongahela River, PA 148, PA 148 Truck, and PA 148.^[4][5] As of 2022, the route is still intact;^[6] however, any weight restrictions on Wylie Creek bridges were removed by 2021.^[7]

The entire route is in Allegheny County.

•   U.S. Roads portal
•   Pennsylvania portal
• Mon-Fayette Expressway

• Pennsylvania Highways: PA 48