The first extension during the mid-1940s shifted PA 39's eastern terminus to the junction of Hershey Road and Allentown Boulevard (US 22) south of Manadahill.

The trail splits south at the Industrial Road intersection before PA 39 approaches an interchange with the US 22/US 322 freeway at the northern tip of Wildwood Lake.

East of the exit, the highway reverts to two lanes and passes through the predominantly residential northern suburbs of Harrisburg.

Outside of the village, the amount of development along the highway declines as the route passes through areas of forests and open fields, crossing Beaver Creek.

It heads south from Jonestown Road to intersect US 22, here an at-grade roadway named Allentown Boulevard, near Skyline View.

During this stretch, it passes through South Hanover Township and serves the communities of Hanoverale and Union Deposit.

It passes under Norfolk Southern Railway's Harrisburg Line, then enters a highly developed area east of the borough of Hummelstown.

[8][9] The remainder of current PA 39 north of Swatara Creek was a state-aid route designated A-306, which ran from South Hanover Township to Union Deposit.

The Dill plan proposed rerouting US 22 along Linglestown Road from Harrisburg to Manadahill, replacing PA 39.

[12] A new highway around the eastern fringe of Union Deposit was constructed in 1968 and opened to traffic as a realignment of PA 39, later that year.

[17][20][21] Park Boulevard in Hershey was rerouted in 1973 to intersect the new bypass and provide a direct connection between Hersheypark and PA 39.

[22][23] In the early 1970s, the portion of PA 39 in Susquehanna Township from North Sixth Street to Laurelwood Drive was converted from a two-lane roadway to a four-lane divided highway as part of the construction of the US 22/US 322 bypass.

[22][24] To the southeast, the segment of PA 39 south of West Chocolate Avenue near Hummelstown was rebuilt as a divided highway ca.

[26] At the same time, West Hanover Township made improvements to the area surrounding PA 39's interchange with I-81.