PA 873 begins at an intersection with PA 309 in the community of Schnecksville in North Whitehall Township, Lehigh County, which is in the Lehigh Valley. From this intersection, the route heads north on a two-lane undivided road, passing a mix of homes and businesses. The road turns northeast and passes residences and fields before intersecting the western terminus of PA 329. From here, PA 873 continues north into the residential community of Neffs before curving northwest and entering Washington Township. In this area, the road passes through a mix of housing developments and farmland as it turns north and passes over Interstate 476. The route continues through rural areas of homes and woods prior to crossing into the borough of Slatington. Here, PA 873 becomes Main Street and is lined with residences before reaching the commercial downtown, where the road makes a sharp turn to the east. The route turns north onto Walnut Street and passes more businesses before running past a few homes a short distance to the west of Slatington Airport. PA 873 leaves Slatington for Washington Township again and runs through wooded areas with some residences. The route turns northeast, with the Appalachian Trail joining the road, and crosses the Lehigh River into Lehigh Township in Northampton County, where it passes over Norfolk Southern's Lehigh Line before ending at PA 248 at the base of Blue Mountain south of Lehigh Gap. The Appalachian Trail turns south onto PA 248 at this point.
History
When Pennsylvania first legislated routes in 1911, what is now PA 873 was incorporated as part of Legislative Route 163, which ran between Allentown and Mauch Chunk. With the creation of the U.S. Highway System in 1926, the section of road between Schnecksville and Lehigh Gap was designated as part of US 309, a route that ran from Philadelphia north to Wilkes-Barre. At this time, the entire road was paved. PA 22 was designated concurrent with US 309 on this stretch of road in 1927. A year later, PA 130 replaced the PA 22 designation along US 309. By 1930, the concurrent PA 130 designation was removed along this stretch of US 309, which intersected PA 29 in Schnecksville and PA 45 in Lehigh Gap. US 309 was shifted west to a new alignment between Allentown and Hazleton in the 1950s, and PA 29 was shifted east to follow the road running between Schnecksville and Lehigh Gap. On May 9, 1966, the PA 29 designation between Allentown and West Nanticoke was removed, splitting the route into two segments. As a result, PA 873 was designated onto the former alignment of PA 29 between US 309 in Schnecksville and PA 248 in Lehigh Gap.
