Zoo Interlocking (MP 1.9) is a large double-overlaid wye, connecting the tracks southeast to 30th Street Station (both low-level and high-level) on separate tracks, with the latter west of the former, with the tracks northeast to North Philadelphia (and New York City) and the tracks northwest to Parkesburg and Harrisburg. The elevated tracks from 30th Street High-level cross over the west leg of the low-level wye just north of its south apex, after which the higher-level tracks have their wye within the confines of the lower-level wye, with the added complication that there is a flying junction separating the tracks by direction at the northeast apex of the wyes. The speed limit is 30 mph through the wyes and interlockings at Zoo. The tower once stood on the north side of the south-to-east leg, lower level.
Now double track, the overhead AC electrified line heads northwest, with speed limit 60 mph, past two road bridges overhead, a line to the west, a track in the center rising up from the underpass carrying it from the North Philadelphia direction, a total formation width of five tracks, four road bridges overhead, one of which is a bowstring girder bridge, crossovers at Stiles (MP 3.5), where the line from the underpass joins into the main four track formation, and crossovers at Valley (MP 4.0), where the SEPTA Ivy Ridge line rises up on a stone viaduct, past a disused station on the viaduct, and departs to the north of the Main Line on a flyover from the second southernmost track with a through bowstring truss bridge crossing two mainline tracks and the yard lead, on the north side, to the SEPTA Ivy Ridge maintenance facility on the west side of the departing line, with a track from the north side of the main line running under the bridge and rising on the west side of the branch line, with a line trailing back in at the west end.
There are signals and crossovers along the four remaining tracks at Paxon (MP 4.1), the Ivy Ridge through bowstring truss bridge overhead, the SEPTA Ivy Ridge maintenance facility on the north side, a road bridge overhead, a bridge over a street, extra track on the north side (the west lead from the maintenance facility, a gentle curve to the north-northwest through the western Philadelphia suburbs along the so-called "Main Line", past the signals and crossovers (where the arrangement of four tracks as slow, fast, fast, slow, starts) and passenger station with two low-level side platforms, a brick tower, and brick depot to the south at Overbrook (MP 5.4), where line speeds of 70-35/25 start, a road bridge overhead, a signal bridge for the west end of the Overbrook crossovers, a curve north at the passenger station with two low-level side platforms and a brick depot on the south side at Merion (MP 6.0), past two road bridges overhead, then northwest (with 60 mph passenger speed limit on the curve) at the passenger station with two low-level side platforms and depot to the south at Narberth (MP 6.8), where there is a bridge over a street at the west end and freight speeds rise to 35/30, and west to the passenger station with two low-level side platforms and a depot to the south at at Wynnewood (MP 7.5).
The line turns northwest past a road bridge overhead, a spur trailing in on the north side, the passenger station with two low-level side platforms and brick depot to the south at Ardmore (MP 8.5), a road bridge overhead, the passenger station with two low-level side platforms with umbrella sheds and a depot to the south at Haverford (MP 9.1), MP 10, a bridge over a street, the signal bridges and crossovers within the station area, a brick tower to the north, and passenger station with two low-level side platforms and depot to the south at Bryn Mawr (MP 10.1), a road bridge overhead, a bridge over a street, the passenger station with two low-level side platforms and depot to the south at Rosemont (MP 10.9), and the passenger station with two side platforms at Villanova (MP 12.0), with a road bridge overhead at the west end followed by a bridge over I-476 below.
The line curves west, bridging over the Norristown High Speed line, and past the passenger station with two low-level side platforms and depot to the north at Radnor (MP 13.0), Intermediate Signals on a signal bridge, the passenger station with two low-level side platforms at St. Davids (MP 13.8), the passenger station with two low-level side platforms and brick depot to the south at Wayne (MP 14.5), a bridge over a street, a road bridge overhead, the passenger station with two low-level side platforms and a depot to the south at Strafford (MP 15.4), where there was once a connection on the south side from what is now the High Speed Line, two bridges over streets, a road bridge overhead, a street alongside to the south, detectors for both directions at MP 16.3, the passenger station with two low-level side platforms and depot to the south at Devon (MP 16.5), a street alongside to the south, a curve to the west-northwest, a bridge over a street, a curve to the west again, the passenger station with two low-level side platforms, a depot to the south and a footbridge overhead at Berwyn (MP 17.5), a road bridge overhead, MP 18, a signal bridge, the passenger station with two low-level side platforms at Daylesford (MP 18.6), a street alongside to the south, crossovers, a bridge over a street, crossovers, a signal bridge, a brick tower on the north side, and the passenger station with two low-level side platforms with umbrella sheds and a brick depot to the south at Paoli (MP 19.9, terminus of many SEPTA trains, a road bridge overhead crossovers (with a signal bridge, where four tracks end, with speed limits of 65/60-30-20 in the interlocking), a closed signal tower on the north side, and a SEPTA yard on the north side of the line west of the station.
Continuing west, with speed limits now 90-50/40, except 75-40 on some curves, the line passes a bridge over a road, a street alongside to the north, the passenger station with two low-level side platforms at Malvern (MP 21.6), a bridge over drainage, a street alongside to the south, a bridge over a stream in the woods, crossovers at Frazer (MP 23.9), the tracks separating, the north track bridging over a double-track line that rises between the tracks, where there is an eastbound detector and a PRR line once crossed from north to south, a bridge over a street, a road bridge at an angle overhead, crossovers at Glen (MP 25.3), where the former Conrail line in the middle trails in and the line becomes three tracks wide, with the third track (track 2, in the middle) having only a 30-25 speed limit while the others are 90-50, the passenger station with two low-level side platforms at Exton (MP 27.5), a bridge over a street, Whitford (MP 28.3), where a freight line bridges overhead on a through truss bridge from the northeast to the southwest.
There is a bridge over a street, a signal bridge, a bridge over a street, a road bridge overhead, extra track on the north side, a road bridge overhead, crossovers at Downs (MP 32.1), where a former reading line from Norristown trails in on the north side and four tracks start (the additional track 3 is 60-40 to add to the existing speed limits on the others), a bridge over a street, a bridge over a river, the passenger station with two low-level side platforms at Downingtown (MP 32.4), a bridge over a street, a street alongside to the north, a substation on the south side of the line, a tunnel on the south two tracks only, a bridge over a street, crossovers at Thorn (MP 35.0), where a fifth running track starts, a former roadbed descending between the north tracks and the south tracks, crossovers at Caln (MP 36.6), where the fifth running track ends and there is an old tower on the north side, a disused passenger station with two side platforms, a large space between the north tracks and the south tracks, a signal bridge, a bridge over a road, an angled road bridge overhead, three bridges over streets, and the passenger station with two low-level side platforms at Coatesville (MP 38.4).
There is a bridge over a road and a north-south rail line below (the former Reading Beaver Valley line, a road bridge overhead where the road alongside crosses, an embankment, a signal bridge, westbound detectors at MP 39.0 (hot box), a bridge over a street, a bridge over a stream, and a bridge over a street below, westbound detectors at MP 39.9 (dragging equipment), crossovers, a bridge over a road, two road bridges overhead, two bridges over streets, a track descending in the center and passing beneath the south tracks, which then come back together with the north tracks, three road bridges overhead, a signal bridge in farming country, a road bridge overhead, a spur to industry on the south side, a substation on the south side, a signal bridge, a road bridge overhead, a bridge over a stream, crossovers at Park (MP 43.9), where four tracks end and speed limits on the through tracks are 70-40, extra track on the south side, a road bridge overhead, a spur to the south, a bridge over a river, a spur to the south, a road bridge overhead, a signal bridge, a grade crossing, a bridge over a road, and the passenger station with two side platforms at Parkesburg (MP 44.2), the west end of SEPTA service.