Interstate 79 is the primary north-south route in western Pennsylvania. Generally, the freeway follows U.S. 19, but while U.S. 19 enters Pittsburgh, I- 79 bypasses it to the west. Through western Allegheny County, I-79 winds northward through South Fayette township and the borough of Bridgeville. The freeway expands to six lanes north from PA 50 (Exit 54), with commuter traveling swelling traffic counts to 94,000 as recorded by Penndot in 2016.
Making a number of S-curves, I-79 proceeds north through the Collier township by the boroughs of Heidelberg and Carnegie. A modified cloverstack interchange follows with I-376/U.S. 22-30 (Penn-Lincoln Parkway West) near Pennsbury Village. Usually referred to as simply Parkway West, the freeway taking I-376 east into Pittsburgh was previously I-279 and part of the original planned alignment for I-79.
Northward into Robinson township, Interstate 79 reduces to four overall lanes. Still well used by commuters with 65,000 vpd recorded in 2016, the freeway crosses paths with PA 60 at Moon Run and continues north with a forested median between an array of subdivisions along the Kennedy township line.
Interstate 79 curves sharply ahead of the Ohio River as it lowers to span the Back Channel and Neville Island. A six-lane tied-arch bridge crosses the main channel of the Ohio River at the borough of Glenfield.
Navigating through a valley fed by Kilbuck Run, I-79 advances north through Aleppo township, Sewickley Hills and portions of Ohio township. Interstate 279 converges with the freeway in the borough of Franklin Park, with I-79 widening to six lanes and 2016 traffic counts reaching 100,000 vpd. The six-lane section extends north to U.S. 19 (Perry Highway) in Marshall township. I-79 meets the PA Turnpike nearby and the crosses the Butler County line.