PRR Interlocking Diagrams: Philadelphia to Harrisburg Main Line

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Amtrak maps of this area available on Ken Reinert's Zoo to State page.

Main Line -- Philadelphia to Harrisburg

BROAD, Philadelphia, Pa. (111K, ?75 dpi)

Starting point of outbound suburban trains. BROAD "tower" is a room in the basement of Suburban Station (i.e., below street level, on the concourse level) which controls from this station to the upper level of Pennsylvania Station (30th St.), where trains are handed off to either ZOO or ARSENAL.
John Cooper notes the following changes: All signals now display Restricting instead of Stop-and-Proceed (since the 1989 reworking of the interlocking plant). All high signals have full circle instead of cropped-sides bottom face. Signals 38R and 40R can at best display Approach Slow instead of Approach Medium. This corrects an error where 38R,40R would display approach medium before a slow-approach or slow-clear. 50R (Arsenal) is gone and moved up to the point where the 33T label is. The Grey's Ferry switch is gone, so a clear indication is now possible. 261 [bidirectional signalling] is installed on both Maryland Division tracks. Cab signals have been installed on all tracks, starting at 110L, ending at 48R (previously, cab signals ended at 42L and 64R of ZOO). Switch 69 has been removed. The tunnel is extended (eastward) from Trk 9, 7, 6, NewTrack-call-it-4. Station tracks 8 and 5 have been removed to make an extra-wide platform. The straight path from Trk 1 has been removed. The 117/119 scissor crossover is gone. 121 is gone from Trk 6. The track detours near B2 to realign to where Trk 4 would be. There was room S of Trk 5 for 4 storage tracks that were never built -- this has been used for NewTrack-call-it-4, a narrow platform, and another station track. The station tracks have been renumbered 0-7, with 1-4 being the through tracks.

Connection, past Pennsylvania Station (30th. Street Station) Upper Level platforms, southward (RR-south) to Washington main line, with the West Chester Branch veering off soon.

ZOO, West Philadelphia, Pa. (238K, 300->150 dpi)
ZOO, part 1, West Philadelphia, Pa. (170K, 300 dpi)
ZOO, part 2, West Philadelphia, Pa. (254K, 300 dpi)
ZOO, part 3, West Philadelphia, Pa. (245K, 300 dpi)

On the west side of the Schuylkill River in Philadelphia. Probably the biggest and busiest junction of mainlines on the Pennsy, if not in the United States as a whole. Point of convergence of the main line from New York City with that from Harrisburg and Pittsburgh to reach Pennsylvania Station (30th St.) in West Philly and ultimately Wilmington, Baltimore, and Washington. Tracks existed on 4 levels, rising and falling as needed to keep traffic flowing with a minimum of conflicts. Images are 300 dpi; diagram is from 1971.

Connection southward (RR-east) via High Line to Washington main line.
Connection northeastward (RR-east) to New York main line.
Connection northward (RR-west) to Reading RR at BELMONT.

OVERBROOK, WOODBINE, VALLEY, Overbrook, Pa. (129K, 150 dpi)

Just off City Line avenue, on the border of the city and suburbs. Site of the first, experimental colorized Stop aspect. A true Pennsy classic is shown: the flyover (flying junction; duckunder). Interlocking plant now substantially changed to, it appears, allow high-speed swap of inside and outside tracks.

John Cooper notes that currently, Trk #4 west of the flyover from Sw. #67 to the Woodbine signal bridges is gone. The embankment has been bulldozed to accomodate a new engine and car shop facility. The yards on either side of the flyover have long since been abandoned - 10 or 15 years. The eastern part of the yard may have even been sold. The whole yard has always been a headache for the Pennsy because it's not level. A new track north of Trk #2 has been added under the flyover which realigns to Trk #4 somewhere between the two woodbine signal bridges. A crossover has at 44th St. has been added at 146L for Paoli locals to get to the new track. To the east, the new track becomes what is labeled as the EWD Jersey track on the ZOO diagram.

Connection northeastward (RR-west) to Schuylkill Branch.

BRYN MAWR, Bryn Mawr, Pa. (83K, 150 dpi)

Next tower west on the main line to Pittsburgh. Site of the "Bryn Mawr Turn", a local commuter train that crossed from #4 (outer W/B) to #1 (outer E/B) track at this location. (Other trains went on to Paoli.) Also top of the grade from the Schuylkill; some freights required helpers on this hill.

John Cooper notes that the Trk #1 (E/B) distant signal is actually controlled so that the the local could cross over the railroad and make a protected move past the E/B home signal.

PAOLI, Paoli, Pa. (96K, 150 dpi)

End of commuter train territory in Pennsy days; the growth of the megalopolis has now extended this territory significantly, though Paoli is still the end of the high-density settlements. Tower controlled main line switches and yard entrance. The yard is, unfortunately, not shown, and only portions of the (quite tight) loop track are shown. This loop was used to turn the commuter trains and bring them to the inbound side of the main line. Commuter trains were serviced in this yard. The facility was closed by SEPTA, in part because of PCB contamination. PCBs were used as transformer coolants.

DALE, GLEN, Thorndale, Pa. (49K, 200 dpi) [1]
A later, Penn Central version (32K, 150 dpi)

Connection eastward to the Trenton Cutoff. See also THORN, immediately below.

THORN, CALN, DOWNS, Thorndale, Pa. (67K, 200 dpi) [2]
A later, Penn Central version (68K, 150 dpi)

Beginning of the Trenton Cutoff, built to connect the Pittsburgh and New York main lines while avoiding the congestion, roundabout routing, and grades involved in going through Philadelphia. Of course (!), flyovers were used to separate the two lines. This is also the site of one of the 3 (?4) phase breaks, and the 8-lights-in-a-circle phase break signals are seen on the diagram.

A 1969 version [coll. of Jon Roma, ref. 2] shows the hot box detectors W of the 391 signals, as on the 1972 diagram, but 2 tracks remaining on the P&T Branch, as on the 1963 diagram. As these changes are already well represented on the existing maps, I chose not to scan yet a third version.

Present status: Trenton Cutoff is presently 1 track, unsignalled, to CP-Ernest (near Norristown) where the connection from the Reading main was renewed. Signals replaced from there to Morrisville Yard.

PARK, Parkesburg, Pa. (48K, 200 dpi) [3]
A later, Penn Central version (41K, 150 dpi)

End of present commuter territory. Site where the Low Grade line (Atglen & Susquehanna) branched off toward Quarryville, Columbia, and Enola (avoiding Elizabethtown grade and passenger traffic). Yet another flyover was used to achieve this. Low Grade is presently abandoned to CP-Port (near Creswell), except for a short stub at PARK where SEPTA parks a train occasionally. Lately (under CR) little used due to 10 MPH speed restriction (falling rocks). The portion from PORT to Enola is still in place. A portion of the A&S Branch bridge over the Susquehanna River N (RR-W) of Columbia washed out in Hurricane Agnes (1972).

[3A] LEAMAN, Paradise, Pa.

22K, 200 dpi Named after Leaman Place; pronounced 'lemon' by locals. A temporary block station, usually opened only when there was local track work, to be able to switch trains off the 'wrong-running' main at manually operated switches. This was useful because of the rather long distance from PARK to CORK and the unidirectonally signalled tracks.

Connection southeastward (RR-west?) to the Strasburg RR.

[4] CORK, Lancaster, Pa.

108K, 200 dpi

Connection westward to the Columbia Branch.
Also connection, via Dillerville Yard, to track via Water St., part of original main line, which ultimately ran all the way to Quarryville on the A&S Branch.

[5] LANDIS, Landisville, Pa.

29K, 150 dpi
West of Lancaster, crossing of the Reading Railroad's branch to Columbia, Pa. One of the few (if not the only) at-grade railroad crossings on the Pennsy mainline in Pennsylvania.

[6] ROY, Royalton, Pa.

46K, 200 dpi
A 1957 version, showing the Columbia Br. as double track (43K, 200 dpi) [thanks to Steve Bundick for scanning]

Connection southward (RR-east) to the Columbia Branch (later renamed "Royalton Branch" by Conrail).

[7] STATE, Harrisburg, Pa.

104K, 200 dpi

Connection westward to the Cumberland Valley Branch.

[8] HARRIS, Harrisburg, Pa.

90K, 200 dpi

Connection southeastward, then eastward, to the Reading RR Lebanon Valley Branch (eastward to Reading) and Lurgan Branch (westward to Chambersburg, thence southwestward via Western Maryland Rwy. to Hagerstown). The LV is currently Conrail's main line across eastern Pennsylvania.

Mark's Railroad-Related Stuff
The Broad Way: A Pennsylvania Railroad Home Page
Maps of the PRR
Interlocking Diagrams
Philadelphia to Harrisburg: Main Line

Mark D. Bej
+1 216-444-0119