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Monday, February 15, 2016


So it's been a while since we last visited the PRR Main Line and this time I have something special.  OVERBROOK interlocking, straddling the border between the city of Philadelphia and Montgomery county, is not only an important part of past and present Main Line services, it is also an active interlocking tower dating from 1926 with all of the PRR trademarks on display for all to see.  OVERBROOK and its interlocking is highly accessible, being located in the middle of a commuter station.  However what makes this tower truly special is that in the 2003-2004 time period I was able to visit it on several occasions and spent hours inside watching the operations and even working the U&SS Model 14 machine.  This will be the first of a three part look at OVERBROOK, the first covering OVERBROOK interlocking, the second OVERBROOK tower (inside and out) and the third OVERBROOK's CTC territory.

OVERBROOK is the first typical crossover interlocking on the Main Line after ZOO.  It was later expanded to include the west end of the old Belmont Freight yard and CTC control over the junction with the old Schuylkill River branch at VALLEY interlocking, but the core of its operations were the 4-track crossover tracks that ran the length of the station.  Here is a 1972 interlocking diagram showing OVERBROOK's territory at the peak of its responsibilities.

The origional 4-track crossover part of the interlocking controlled by the US&S Model 14 interlocking machine dates from 1926.  In 1941 OVERBROOK assumed control of the west end of PRR's 52nd Street Yard, situated between the main line passenger tracks stretching between OVERBROOK and ZOO by means of a direct wire relay interlocking. Not a separate interlocking in its own right, this new territory was made part of OVERBROOK interlocking itself, but referred to as the "Woodbine" section of OVERBROOK on signaling documents.  OBERBROOK was also given CTC control over the aforementioned VALLEY interlocking on the Main Line and JEFF interlocking on the Schuylkill branch.  Woodbine, VALLEY and JEFF were all controlled from a new US&S unit lever CTC machine installed on the operator's desk in the bay window and is the reason OVERBROOK is shown with two interlocking machines on the diagrams.  Finally, in 1964, OVERBROOK was given one last CTC interlocking, MANAYUNK, when the Schuylkill branch was cut back to a single track at that passenger station.  Here is how OVERBROOK appeared after 20 years with Amtrak in 1992.

You can see that Woodbine and the old 52nd St yard complex has been greatly diminished as freight traffic left Amtrak territory in the 1980's.  VALLEY has also been simplified, JEFF has been transferred to SEPTA control and MANAYUNK no longer exists after passenger service was cut back to Cynwyd.  Finally here is how OVERBROOK's territory looks at the time of this writing in 2016.

The biggest change is the route that Main Line passenger track 4 takes between ZOO and OVERBROOK.  Previously it had flown over the freight yard complex on a long truss bridge at VALLEY interlocking.  (That is how freight traffic was able to access the yard from the middle tracks at OVERBROOK).  However in the early 1990's twin crises emerged with a common solution.  PCB from the former PRR electric MU shoppes at Paoli had contaminated large parts of three counties and the VALLEY flyover bridge was rapidly deteriorating and could no longer support passenger train speeds. 

Realigned track 4 (far left) and the old VALLEY flyover.
The solution was to shift track 4 over to run adjacent to tracks 1 and 2 on the site of the former freight yard and then build a new SEPTA MU maintenance facility on the newly available space.  This had the side effect of requiring three new interlockings, STILES, PAXON and WOODBINE (not to be confused with OVERBROOK's Woodbine section mind you), which would then be controlled by ZOO, as it had a leverman job to support the extra workload.  The effect on OVERBROOK proper was the further truncation of the Woodbine section, removing the #14 and #15 running tracks the 017 switch.  This left only a triplet of signals, the 20R and 018R, and a single switch, the 019.  The reason for the leading zero was to differentiate levers on the CTC machine from levers on the Model 14 machine.

The westbound 018R signal at OVERBROOK's Woodbine section.
As I mentioned before, OVERBROOK's Woodbine section was located directly adjacent to the new Amtrak WOODBINE interlocking, but confusion was minimized through the use of colorized position lights on the newly hardware.

1941 PRR PL vs 1994 Amtrak PL. Taste the difference!
 Originally intended for terminal freight moves, the 019 is a slow speed switch with Slow Approach displayed for diverging routes on high PRR signals.  The best indication the 018R can give is Approach Medium for a diverging route over the 17 switch at OVERBROOK.

OVERBROOK 018R displaying Slow Approach over the 019 switch reverse.
Eastbound movements at OVERBROOK's Woodbine section were provided with a 4-track signal bridge hosting signals for the center tracks 2 and 3.  In 1994 the bridge was re-purposed to also support WOODBINE's eastbound home signal as well.  Tower, between OVERBROOK and ZOO, all 3 tracks are technically bi-directional, although reverse movements on #1 track will encounter a string of PL dwarf signals displaying slow speed indications.  Prior to 1994 track 4 was only signaled for westbound movements, but this was upgraded when the three new interlockings were added. As you can see, due to its slow speed and somewhat redundant nature, the track 3 route over 019 switch isn't used much, but the famous 4-track main line does start here.

I should also mention that OVERBROOK was the site of a 1954 experiment to equip the upper head Stop position with red lenses, a measure that was later adopted by the Penn Central and Conrail.  However Amtrak did not embrace this modification (at first) and OVERBROOK was converted back some time after 1976.

OVERBROOK 20R displaying Slow Approach over the 019 switch reverse.
WOODBINE interlocking, that provides a seldom used westbound exit from SEPTA's Overbrook maintenance facility, is notable for the frequently displayed Slow Approach indication on its westbound mast signal.  This is due to OVERBROOK's rather unique layout involving pocket tracks.

Only a few hundred feet separate the eastbound Woodbine signal bridge from OVERBROOK's westbound signal bridge.  Despite all 4 tracks being technically bi-directional, only tracks 2, 3 and 4 (from left to right) are given high signals on the bridge as reverse movements on 1 are exceedingly rare and made at slow speed (no cab signal code).  However they are still made under signal indication without a track warrant. Track 2 is Rune 251 in the eastbound direction west of OVERBROOK so its 14R signal does not provide straight route indications.  The 12R and 8R signals on tracks 3 and 4 do have Clear indications (as seen on the 8R) however you might notice the absence of an Approach / on the upper head.  This is due to the short distance between the westbound gantry and the pocket exit signal on track 4 or the interlocking exit signal on track 3.  While most railroads would use speed control followed by a straight approach for short signal blocks, the PRR was on of the few that would follow it up with a Slow Approach.  This was due to the availability of a slow speed indication on standard high signals.

 Adjacent to the westbound OVERBROOK signal bridge we find the interlockings beefy air plant.  The compressor and air drying equipment was likely moved out of the tower's first floor when the Woodbine relay equipment was added in 1941.  In 2003 the backup generator was a new addition, probably purchased with a homeland security grant.

 OVERBROOK interlocking proper is a fairly standard 4-track interlocking that also includes a dump track for MoW vehicles and two station pockets that allows express trains to literally leapfrog slower locals.  A similar setup can be found at BRYN MAWR interlocking, but only on the westbound #4 track.  OVERBROOK has signaled pockets on both #1 and #4 tracks. With the removal of freight traffic freeing up the center tracks for express passenger operations this feature is not as useful as it once was, but it is still used on occasion

OVERBROOK's #15 turnout facing westbound. Have fun maintaining a track profile in three dimensions.
OVERBROOK's primary purpose is now the sorting of local and express trains onto and off of their respective tracks via the 9 and 15 switches.  In this photo one can also see that OVERBROOK contains the bane of track maintainers everywhere, turnouts on curved, super-elevated track.  

Here we see OVERBROOK tower and its relationship to the Overbrook station platforms.  The extra long curved turnout blades are provided with an additional point detector switch to make sure they are in the fully locked position along their entire length.

The 16L signal governed movements out of the eastbound station pocket and over the trailing 15 switch.  The 16L featured an interesting progression due to the signal spacing in VALLEY interlocking.  After the lever was restored the signal would display Restricting, then Slow Approach, then Approach Medium and finally Clear.  This sequence is often encountered as OVERBROOK operators will often have local trains waiting or about to wait for an express to cross in front of them.  The 16L is one of the few cases where a fully equipped PRR PL high signal does not actually display any diverging indications.

The "Dump Siding" off 4 track east of the station platform is most frequently used for MoW equipment storage.  It is equipped with a split point derail to prevent runaways from rolling onto the main line and governed by the 6L PL dwarf signal.

The US&S model A-5 pneumatic point machine for the dump siding 7 switch is painted black and plainly labeled in yellow like all the point machines in the interlocking plant.

The  6R dwarf signal governs movements both into the Dump Siding and reverse out of the track 4 pocket.  The lack of indications more favorable than Restricting is left over from former the single direction status of track 4.  Fun Fact, Track 4 between OVERBROOK and WOODBINE is governed by Interlocking Rules, so track cars can have signals displayed for movements approaching WOODBINE.  Here the 6R signal is displaying Restricting for a movement into the dump siding.  The adjacent #9 switch is seeing a bit of rush because in 2003 the center tracks were not regularly used on weekends, express Keystone trains being slotted to run between SEPTA locals on tracks 1 and 4.

Not every switch in OVERBROOK's main plant was good for Medium Speed.  The #11 switch between tracks 2 and 3 was only a Slow Speed turnout.  The reason was because it would only be used by westbound trains on a Restricting preparing run reverse on tracks 1 or 2 or used by eastbound trains planning to run reverse on track 4 or into the 52nd St yard.  Use of a #10 turnout reduced the length of the turnout as well as maintenance costs.


The 17 switch was rated for Medium Speed as west of OVERBROOK the #3 track was signaled for bi-directional running and would occasionally see eastbound movements needing to cross to tracks 1 or 2 (seeing as track 3 went into the yard and track was westbound only).  Here we see an outbound SEPTA local waiting in the "pocket" for an express train to pass it by.  The 9, 13, 15, 17 and 19 turnouts are actually #20, which are typically good for limited speed, but for whatever reason were kept at medium.  Another "feature" of having an interlocking within a station is the lack of track fences to keep people from crossing the track.  This provides Overbrook Station with uncluttered sight lines for photography.

The 10R pocket exit signal serves the same purpose for westbound trains on track 4 as the 16L does for eastbound trains on track 1. Unlike the 16L there is no complex progression so the lower head consists of a bare Restricting \. 

Here we see the same 10R displaying a Restricting to a SEPTA local moments after it was leapfrogged by an express Amtrak Keystone train.

Here is the west end of OVERBROOK interlocking showing the 19 and 13 turnouts as well as the 10R and 18R signals.  The 18R dwarf PL is used for Reverse movements out of the track 1 pocket and against the flow of traffic westward.

Here we see the original western limits of OVERBROOK interlocking.  The 19 and 13 switches both end at this 4-track signal bridge and are accompanies by the 10L reverse direction dwarf signal on track 4.  However the signal bridge is empty. 

A few hundred feet to the west (and with the Marion station in view) we finely stumble upon OVERBROOK's eastbound signal bridge.  There is also a little bonus in the form of the 4R semi-automatic exit signal on track 3.  This almost certainly was installed to simplify the logic for the bi-directional capability on track three west of the interlocking. It is semi-automatic in that it will behave like an automatic until the lever is restored to the Stop position. 

Here we see the eastbound signal bridge from the opposite direction.  From left to right we see the rear of the 4R Semi-auto,  the 12L, 14L and 18L high PL signals.  The 12L signal lacks a | on the upper head as the best indication it can give is Approach Slow for a Slow Approach on the 20L signal for routes over the 019 switch.  The 14L signal is actually displaying Medium Clear for an approaching Keystone train crossing over from express track 2 to local track 1.  Trains can run all the way into ZOO on track 2, but this can create conflicts in that interlockings JO section so the operators almost always run eastbound trains on track 4. Finally the 18L is at Stop, but could be displaying Slow Approach for a stop at the 16L signal if an inbound local train were also approaching.  The upper head / is for Approach Medium indications or Approach Slow indications for trains approaching restrictive signals at the 018L or 16L.

Although not part of OVERBROOK interlocking proper, the 68 distant signals at Narberth are notable as they show am Approach Medium indication for trains approaching OVERBROOK, but not an Approach Slow.  This means trains approaching a Stop at the 16L or 018L do not see an Approach Slow before a Slow Approach.  I suspect they see Approach to Slow Approach.  A similar setup was seen on track 4 westbound before WOODBINE interlocking was installed.  Also visible in this photos are the dragging equipment detectors that sound an alarm inside OVERBROOK tower.

Well that is all for the tour of OVERBROOK interlocking.  Next time in this series we will venture inside OVERBROOK tower itself to check out how it is operated along with its big iron.

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