From the junction at CP Harris (MP 21.9), where it departs the north side of the Amtrak line to Philadelphia, as the freight line turns away on the north side, the single track, CTC, line with speed limit 50 mph, but a 40 mph speed restriction to MP 21.0, follows the north side of the Amtrak line, past Harrisburg station's north side, and a crossover from that line, beneath the former Reading line coming across the Susquehanna River to join the freight line turning away, and runs southeast along the east bank of that river on the north side of the Amtrak line, past a road bridge overhead, a highway bridge overhead, and a road bridge overhead, Steelton (MP 17.9), with Bethlehem Steel's Steelton Plant on the northeast side of the line for several miles, a detector at MP 15.9, and tracks from that plant trailing in at its east end at Highspire (MP 14.8), past Jednota (MP 14.1), a 40 mph speed restriction from MP 14.0 to MP 13.5, a bridge carrying the Amtrak line overhead, a road bridge overhead, the passenger station at Middletown (MP 12.0) on the north side, and CP Roy (Royalton, MP 11.0), where there are crossovers (speed restriction 30 mph), the main line turns south-southeast, while the former PRR Royalton Branch along the east bank of the river heads south.
The branch passes TMI Switch (MP 9.5), immediately adjacent to the Three Mile Island Nuclear Power Station, where there is a spur on the west side of the line, a curve at MP 9.4 (speed restriction 45 mph), curves between MP 8.5 and MP 5.9, with speed restriction 40 mph, as the line turns southeast, then south-southeast , a detector at MP 6.1, Collins (MP 5.9), a 45 mph speed restriction on the first curve north of MP 5.0, CP-Jeb (MP 2.2), where a Controlled Siding on the east side starts, with speed restriction 10 mph as the line turns just south of due east, and CP Shocks (MP 0.0), where the siding ends and the branch trails into the north side of the Enola Branch, heading east.