The principal participants in the South Penn were the NYC and the Philadelphia & Reading. The P&R's most controversial and colorful president, Franklin B. Gowen, financed the South Penn to serve Andrew Carnegie's steel mills in Pittsburgh. Had the line been completed, it would have resembled the New York, Ontario & Western rather than the NYC.
The two best places to see evidence of the South Penn from comfortable seats in an auto are the I-83 bridge across the Susquehanna at Harrisburg (an exit on the west shore leads to the Amtrak/Pennsy station) and the PA Turnpike between Tuscarora Tunnel and the Fort Littleton Exit (Route 522 to the East Broad Top).
From the I-83 bridge, look north to the concrete arch bridge built by the Reading and used by the NS. Approaching the west shore (Lemoyne), tan stone piers are visible through the arches of the bridge. They were built to support 23 iron deck trusses. They converged at the eastern shore to reach the Reading.
The East Broad Top began to construct the Shade Gap Branch to the west portal of Tuscarora Tunnel and graded a site for a yard. Burnt Cabins was to be an interchange, like Mount Union, where freight and passengers transferred between narrow gauge and standard gauge. Today, Route 522 generally follows this line. PennDot stores equipment at the yard site. There, the South Penn grade diverges to the south and east of the Turnpike and swings back west to cross the road east of Burnt Cabins. A viaduct was to cross the South Branch of the Aughwick Creek. The grade crosses the Turnpike again and follows a fairly straight course east of the Turnpike along the west slope of Brush Ridge. Numerous cuts, fills, and culverts mark the right-of-way to a point west of the Fort Littleton Exit, though access to this wild area (like most of the South Penn) is difficult. The grade meets the Turnpike for several miles to Hustontown. Then it swings south.
Author Herbert H. Harwood, Jr., offers a poignant conclusion, as follows:
From the restored 1901 Pittsburgh & Lake Erie station and headquarters building, some creative visualizer can look down from the bridge and imagine the "Philadelphia - Pittsburgh Express" arriving in, say, 1925, behind a heavy South Penn Pacific and watch its through Cleveland and Chicago cars beings switched out to continue west over the Erie-P&LE-New York Central route (p. 148).