Zoo Interlocking (MP 88.0) 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 stands, out of service, on the north side of the south-to-east leg, lower level.
There is a street alongside to the southeast of the center tracks as they curve northeast on the elevated structure over the east-west connector, over the north-south highway along the river (Schuylkill Expressway), and then onto the deck girder bridge over the Schuylkill River. East of the river, the NEC passes through urban Philadelphia, with a connector leaving to the north to drop down alongside the river where it joins the former B&O Royal Blue line. The five track NEC passes crossovers at Girard, passes over that ex-B&O line, with speed limit 70-30, passes a road bridge overhead, a signal bridge, five streets bridging overhead, space for previous other tracks on the north side, a road bridge overhead, a bridge over a street, a signal bridge, more crossovers at Mantua, where the number of track reduces to four, and then runs northeast above the streets of a particularly gritty part of the city, past three bridges over streets, bare concrete pads where buildings once were, on the north side, interlocking box A on the north side, crossovers, a road bridge overhead, a bridge over an angled street, a derelict building to the north, the junction signals, a bridge over a street, the SEPTA Chestnut Hill Branch tracks moving to the north side of the main line tracks, spurs curving away north, and the bridge over the former Reading line coming north from the city center tunnel (and/or the former Reading Terminal, no longer used for trains), to the old tower on the south side at North Philadelphia (MP 85.0), where the station has a south side platform, an island platform on the south side of the main lines, an island platform on the north side of the main lines, with speed limit 60 or 50 through the station, depending on the track, and two curving side platforms on the Chestnut Hill branch, all with umbrella sheds.