Zoo Interlocking to Phil (Philadelphia)

Zoo Interlocking (MP 0.0) 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, and the Hi-Line freight bypass on a tall steel trestle passes overhead, 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 are two stub tracks on the west side (and a small carriage/loco yard on the west side of them) and two through tracks on the east side (with a main highway to their east, along the bank of the Schuylkill River, and a road bridge overhead), with a track on the very easternmost side at a lower level than the others, south of the south apex at Zoo, with speed limits 30-20 to the 34th Street overhead bridge, and then 40-20, crossovers at Penn (MP 1.5), where speeds fall to 30-20 as tracks spread out to all platforms, and Philadelphia's 30th Street Station (MP 1.5), which has five platforms serving ten tracks, oriented north-south at the low level—track 1 is the most easterly, below the great hall with its colonnaded exterior, constructed in the 1930s, and above that the three-platform, six-track, high-level station with its tracks oriented east-west. All platforms are high level, and all tracks are electrified with AC overhead catenary. South of the station, the low-level tracks reduce to two at Signal bridge 20-21, with speed limits rising to 70-50, pass beneath two road bridges overhead, and curve southwest past the crossovers at Arsenal (MP 2.7), where the SEPTA West Chester Line heads away from the high-level tracks on the west side, to the crossovers at Phil (MP 3.6), where a different set of high-level tracks from the high-level station trails in on the west side.

The elevated "high line" freight tracks on the west side of the station, higher even than the high-level tracks, split off from the high-level tracks south of Zoo, and run on their east side, crossing over them at the west end of the high-level station, and descending to rejoin them at Arsenal or Phil. These tracks have been out of use for many years (in 2006).