PA 145 begins at an interchange with
PA 309 in the community of
Lanark in
Upper Saucon Township,
Lehigh County, which is in the
Lehigh Valley. South of this interchange, the roadway continues southeast as part of PA 309 while northbound PA 309 heads west along
I-78. From this interchange, PA 145 heads northwest on Pike Avenue, a
divided highway with two northbound lanes and one southbound lane. The road becomes undivided at the Vera Cruz Road/Oakhurst Drive intersection and ascends
South Mountain with
S-curves, passing through forested areas with some homes. The route reaches the community of
Summit Lawn at the peak of South Mountain, where it intersects Rock Road, which heads southwest to provide access to westbound I-78/northbound PA 309. Here, PA 145 turns north and enters
Salisbury Township, where it descends the mountain with one northbound lane and two southbound lanes through forests with a few residences. At the base of South Mountain, the route heads into the city of
Allentown and becomes South 4th Street, heading into residential areas. The road crosses Emaus Avenue and narrows to two lanes, running north-northwest past businesses as it heads into the Mountainville neighborhood. PA 145 continues past homes and businesses, curving to the north as it passes to the east of a shopping center. After passing through the Mountainville neighborhood, the route turns west onto Susquehanna Street and passes over
Norfolk Southern's
Reading Line and Trout Creek. PA 145 curves north and becomes South 5th Street before it splits into a
one-way pair. The northbound direction follows South 5th Street north and Auburn Street west to an intersection with South 6th Street and
Lehigh Street while the southbound direction follows South 6th Street south and Wyoming Street east. The one-way streets, which carry two lanes of traffic in each direction, pass through urban residential neighborhoods, with northbound PA 145 passing Good Shepherd Hospital along South 5th Street. Past the one-way pair, the route follows Lehigh Street, a three-lane road with one northbound lane and two southbound lanes, through urban residential and commercial areas, crossing
Little Lehigh Creek before intersecting
Martin Luther King, Jr. Drive. After this intersection, the road ascends a long hill. PA 145 splits into another one-way pair at Union Street, with the northbound direction following two-lane South 6th Street and the southbound direction following three-lane South 7th Street. The route heads into commercial
Center City Allentown, intersecting the northern terminus of northbound
PA 222 at West Walnut Street, which is one-way eastbound. A block later, PA 145 intersects West Hamilton Street, with the Soldiers and Sailors Monument located at the center of the intersection between 7th and Hamilton streets. Past this intersection, northbound PA 145 follows North 6th Street and southbound PA 145 follows North 7th Street, with southbound PA 145 passing to the east of the
PPL Center sports arena, where the
Lehigh Valley Phantoms of the
American Hockey League play. Past the arena, the route intersects West Linden Street, which is one-way westbound and serves as the southbound beginning of PA 222. The Allentown Transportation Center serving
LANta buses is located between 6th and 7th streets north of Linden Street. Continuing north, PA 145 leaves Center City Allentown and passes through urban areas of homes and businesses, intersecting
Tilghman Street. A short distance later, northbound PA 145 turns west on two-way, two-lane West Washington Street to rejoin southbound PA 145 at North 7th Street. == History ==