The story of PAOLI interlocking is a story of the Philadelphia Main Line. While today the Main Line is synonymous with wealth and privileged, it started out as just a line of typical agrarian communities that the Pennsylvania Railroad had chosen to build its Main Line through in the first half of the 19th Century. In the second half of said century growing urbanization made the downtown area less desirable as a place to live and as a response the railroad began to encourage development along its main line to help grow the then nascent commuter business. The upper tiers of railroad management were encouraged to live in Main Line communities and the railroad directly financed some development and local infrastructure. By the 1890's the Main Line was growing nicely and the PRR responded with infrastructure upgrades that included ornate station buildings with manicured grounds, closely spaced automatic block signaling to enable a high throughput of trains and finally two new interlockings on the 4-track line, one at BRYN MAWR and the other at PAOLI.
While BRYN MAWR was constructed as a 4-track crossover and intermediate local train turnback, PAOLI was designed as the terminal point for the commuter service along the line. Just about 20 miles from Broad Street Station in Philadelphia PAOLI fist managed the swarm of steam hauled commuter trains and their various combinations of local, limited and express service. Later, in 1915, the busy line was chosen to be host to an experimental 11kv, 25Hz overhead electrification scheme that would rid the upper class area of much of the soot and smoke generated by the steam commuter trains. Paoli would remain as the terminus for the service and would also host the storage yard and shop facility for the new fleet of MP-54 MU cars.
PAOLI tower was built as a mechanical interlocking, even tho power frame technology was available and even installed in nearby BRYN MAWR tower. Originally a 4-track crossover with various connections to the MU yard (including a duck-under to allow MUs to avoid trying up the main with crossing moves), in 1923 the East End was added on a separate electric machine. The East End allowed trains on the center express tracks to access the side platforms without having to platform across tracks 1 or 4. Later the interlocking was completely rebuilt in 1929 with a then state of the art US&S Model 14 Electro-Pneumatic machine replacing both mechanical and supplementary electric frame (probably a table interlocker).
Here is how PAOLI interlocking looked in the late 1960s after the 4th track had been removed west of the interlocking.
PAOLI Interlocking diagram
By this time track #3 east of the interlocking has been made bi-directional possibly either freight trains (which were still an important component of the line's traffic) to run during the busy morning rush, or just due to the fact that the morning rush is more concentrated than the evening rush. Track #2 west of the interlocking was also bi-directional to make up for the loss of the 4th track. This track would eventually be removed entirely as all through freight service dried up and left the then Amtrak owned main line in the early 1980's. The 15/17 and 17/19 switches has been built as double-slips, but by this time has been converted to regular operation. Note the duckunder track for eastbound MU trains entering the main as well as two yard access tracks for westbound trains that allowed a local and express train to exit the main simultaneously. On the East End the 29 and 25 switches allow for express-local crossovers, while I still have yet to discover the operational use for the 27 switch as it is not placedin what would be a more logical setup that allows a platforming train access to the reverse signaled #3 track.
Moving ahead to 1992 we see that #4 track west of the interlocking has been re-connected to allow trains to move straight through on that track without needing a diverging move. #3 track no vanishes at the #11 switch which has been changed from a crossover to a turnout. The Fillout track which allowed storage of an MU set between tracks 2 and 3 has been converted into a stub and disconnected from track #4, although the 2R signal remains to protect the phantom switch. Track #2 has been cut west of the interlocking.
In 1995 more changes came to the Paoli area, although not to the interlocking itself. Since 1915 the MU yard and shop complex had become a major source of PCB contamination due to ignorance about the hazards of the substance. The yard sat on the divide between two watersheds and as such managed to contaminate large stretches of waterway in the batter part of 3 counties. With the Paoli shop not only outmoded technologically, but also constituting a major environmental disaster SEPTA, the commuter rail operator, built a new storage yard at FRAZER, about 4 miles west of Paoli and a new shop complex on a former freight rail yard in the Overbrook section of Philadelphia. The terminal for the R5 service was then moved to Malvern with trains entering and exiting the main line at FRAZER interlocking, which was remote to THORN tower. PAOLI still had the task of routing trains via the local or express tracks and crossing them over from the same. PAOLI would have probably gotten the FRAZER panel if not for a 1994 fire in BRYN MAWR tower that required the interlocking to be re-built. As BRYN MAWR was only open part time in the peak hours to turn the local trains that terminated there the obvious decision was to use the insurance funded capitol project to remote control to PAOLI. The workload for the PAOLI operator was then such that the FRAZER panel went to THORN.
Alright, time for some photos. The tour will run from east to west and as such here is the easternmost point of PAOLI interlocking, the 26L and 28L position light dwarf signals for wrong direction movements on 1 and 2 track.
These signals and the 29 switch they protect are well to the east the signals for 3 and 4 track for some reason. The 29 switch is used by express train to cross over to the inner express tracks.
The 24L an and 22L signals governing 3 and 4 track are mounted on a more modern beam gantry and were probably part of the 1929 rebuild or later electrification project.
The 25 switch is well used by express trains crossing over to platform. Also note the 22R dwarf signal.
Looking at the eastbound signal gantry for the East End we see the 24R, 26R and 28R signals. The 24R has a / on the lower head for the slow speed move onto #2 track. #2 track has only a Stop and Proceed marker lamp and the 28R has a lower head that provides for the Medium Speed regular movements from the local to express track.
In this picture take from the westbound platform at the Paoli passenger station we see an outbound SEPTA MU with a Clear signal displaying on the 28R signal behind it for a eastbound MU.
Here from the Eastbound platform we see the same 28R signal displaying Medium Clear for an approaching Amtrak Keystone train. Amtrak trains often run express between here and OVERBROOK interlocking after making a station stop here at Paoli. The eastbound gantry at the East End is notable for its use of non-integral backing plates for the lower position light heads. These are a vestige of the original position light experiments around 1918 where backing plates for both heads were mounted on the gantry instead of part of the signal heads. Also note the tubular steel catenary supports from the original 1915 electrification and the amount of snot on the center station tracks which are rarely used except for MoW trains and other special movements.
The Paoli station itself was rebuilt in the 1950's for then new PRR President Stewart Saunders. Paoli had always been an important stop for both through and commuter trains and the platforms could accommodate the full 14 or so carlengths of such trains as the Broadway Limited with small shelters (now disused) located along the platform at the various "locations". Anyway, the "fresh and modern" squat brick station replaced the "overly ornate" Victorian station building in the 1950s as a gift to the new president who it was assumed would be using the station. Unfortunately Saunders hated the train and was chauffeured to work ever morning. In 1968 the PRR merged with rival New York Central to form the Penn Central with Saunders as Chairman of the Board. In 1972 the Penn Central went bankrupt due to massive losses in non-railroad investments.
In this view of the Paoli Station platforms we can see the original 1915 44Kv distribution lines that carried 25Hz current for the overhead wires between the generating station in Philadelphia and substations in Bryn Mawr and Paoli. With the end of freight service the lines were decommissioned, with the set on the left being converted later into a 69Kv feeder for the local 60Hz grid. The set on the right were mostly removed except for the short stretch through the Paoli Station which serve no function other than decoration.
For an interesting bit of trivia the only part of the original 1890's station that remains is the canopy covering the stairway from the westbound passenger shelter and the shelter where commuters wait for their automobiles/carriages.
Here is SEPTA Silverliner II #269 as it deadheads west through the Paoli Station. This MU car is special because in the years since it was originally purchased for the Pennsylvania Railroad in 1963 nobody ever bothered to remove the "Pennsylvania" from the letterboards. That such vehicles are still going strong after nearly 50 years in service is a testament to the products designed and built by the Budd Company. For comparison click here for a photo of #269 in the same location posing next to a train of MP-54s.
Back to the interlocking, the westbound signals of the West End are mounted on a small road bridge that connects the two platforms. Here we see the 12L displaying an Approach indication after a recently departed train.
Closeup view of the 12L and 14L signals governing 3 and 4 tracks westward. As #3 track now terminates that signal displays no straight route indications. Both signals retain their classic PRR lower head configuration with a narrow backing behind the | row only.
The 18L "dwarf" signal is also mounted on the road bridge gantry due to the presence of a anti-pedestrian fence between tracks 2 and 3.
Closer view of this unique little signal-bridge. Note the high signals both have the standard maintainer ladders and platforms.
The odd signal out in this lineup is the 20L which governs reverse direction moves on #3 track. This position dwarf is still ground mounted and at least through 2004 it used a non-standard "left handed" position dwarf unit. The PRR type position light is typically right handed with the vertical Slow Clear indication being given on the right side and the Restricting \ being smaller in length than the Slow Approach /. A left handed unit is the opposite with the | being on the left. Aside from making the Restricting \ larger than the Slow Approach /, it also means if the lower Slow Clear bulb is burnt out the signal must be treated as Restricting instead of Slow Approach.
I am not sure if the left handed drawfs are simply an older design or were instead an experiment that took place in conjunction with the right handed signals. The best evidence I have is from photos that show the signals were installed new in some large interlocking plants that were built in the 1930s, but I do not know if they were standard up to that point. If they were then the PRR did a lot of work to replace them with right-handed models. Anyway, here is the left handed 20L signal in 2004.
Here you can see the differences are more than in the shape of the unit. Unlike the right handed models the bulbs in the left handed dwarf are accessed via two plates on the sides of the unit. Also the wiring cable attaches via a bump-out on the back instead of straight out the bottom of the unit. Note the thickness of all the coats of paint that built up over the years.
At some point after 2004 Amtrak got fed up with the non-standard dwarf signal and installed this right handed replacement. It is of US&S manufacture so it may have been surplus from the CORK re-signaling where new Safetran models were installed.
Note the one piece backing for bulb access.
Here we see a snow covered 21 switch as part of the facing point ladder that comprises half of the main crossover part of PAOLI interlocking. In the foreground where a pedestrian path now lays was the location of the 23 switch that lead to the MU layover yard. This switch was primarily used by trains completing their runs as inbound trains would proceed yo the tail track then reverse under the main via the duckunder and re-enter the eastbound track via the 9 switch.
Here is a high def video of a westbound SEPTA local running through the West End of PAOLI interlocking on track #4 as it rounds the curve still within interlocking limits.
PAOLI tower is showing its age with a large brick patch on on its lower level and a large piece of plywood blocking off the location of its bay window that probably succumbed to rot or some such. PAOLI is also suffering from Tower Window Syndrome and as built was fully surrounded by full length double hung windows that have since been boarded over or replaced with modern window types. The tower retained its classic look through the 1960's, but at some point thereafter suffered the blows to its appearance.
In the foreground we can see the 12RA signal which is also left handed. The interlocking has a large number of intermediate reverse direction signals for some reason. Reverse direction movements on #4 track have no fewer than three signals and on #1 and #2 track reverse direction movements each have two signals.
Here we see one of the two west end air compressors that power the point machines on the West End. In this 2010 the compressor unit has been weatherized to prevent the air lines from freezing up.
Here we see the air powered 19 and 17 switches that used to be in a double slip configuration that was eliminated some time in the early 1960's. The left handed 12RA dwarf is more clearly visible here. The double slips were eliminated by moving the 19 switch further down the platform. This would come at the expense of trains making a flat crossing of the main after exiting the yard via the "Hill Track", but with such a move being rare in any event and expansion of the platforms eastward in the 1950's station improvement replacing the lost space on the west end of the platform the modification was logical.
Here is the left handed 12RA signal as well as the 21, 17 and 19 switches as seen from the tower. Note the concrete base for the 21 switch's CP value unit. As the 17 and 19 switches were modified decades later their value units are on less permanent bases.
Wider view of the east end of the west end.
Zooming from the platform in this 2010 shot we can see the the wrong direction intermediate 8L and 4L dwarf signals as well as the full trailing point ladder and the concrete 1915 sub station building which is no longer in use. The mass of overhead wire insulators is a trademark of photos taken at PAOLI interlocking. Note the milepost indicating 20 miles from Broad Street Station in Philadelphia.
A view from the tower of the west end of the west end. On the far left is the old duckunder track and the 9 switch and derail. These were removed between May and December of 2009. They had long since been converted to stubs as all of the Paoli Yard trackage was removed in the post 1995 environmental cleanup. On the right is the old Hill Track stub that functioned as a yard lead with access to the flat crossing ladder of the interlocking.
At the time the Hill Track had been completely removed, but its signal was left in place. This turned out to be a good idea as part of the track was later restored for MoW storage.
Here we see the 10RB signal displaying Slow Approach for some reason. A friendly operator perhaps? ;-)
Here is the west air plant for the West End of PAOLI interlocking. Note the air reservoir is made from sheet steel riveted together to form a tube. Behind it is the ~1938 substation with the catenary section breakers in the foreground.
In 2004 some of the US&S model A-5 point machines were given a bit of refurbishment. Here we see one of the two machines for the 11 switch.
Here we see the air hoses that split to feed both machines for the 5 switch. The far western points are on a curve, which railroads hate for some reason.
As a review to make sure you have been paying attention here is a sequence of photos that shows a train making a full 4 track crossover to wrong rail westbound. We start with the 21 switch in the reverse position.
Pass the left handed 12RA on #4 track.
Traverse the reversed 11 switch.
And the reversed #5 switch. Oh, note the reversed position of the now removed #9 switch. Reversing #5 required #9 to be reversed and vice versa. Operators described this behavior of the interlocking as "quirky" and the need to reverse #9 and its associated risk of failure (it also had a power derail that would need to normal) was probably why the switch was removed.
And finally exiting the ladder at the #5 switch. When turnouts are on a curve which route is actually the diverging one
Here is the #3 switch that leads to the remains of the fillout track. Both it and the #2 track stub are used for MoW storage.
Even this switch seems to have gotten some minor refurbishment and a coat of paint.
As the fillout was designed to store MUs it had a derail to prevent runaways. Note the derail has been lined to the through position. We can see how much use this track gets as the 4RC signal is completely dark.
Here is the 4RC again this time trying hard to display a signal, either Slow Clear or Slow Approach.
The eastbound home signal gantry for PAOLI interlocking holds two high PRR Position Light signals, 6R and 4R, governing #1 and #2 track respectively.
>Here we have the 6R signal displaying a Clear indication.
Here it is displaying Medium Clear for a diverging route from 1 to 2 track.
Here it is displaying Slow Approach for a route onto 3 or 4 track.
Here an Approach signal on 4R joins the Clear on 6R.
And finally a Clear indication on both the 4R and 6R signals.
About 650 feet down track #4 track all by itself is the 2R reverse direction dwarf signal that used to control movements in and out of the west end of the Fillout track. Today is protects nothing, but still must be cleared for all reverse direction movements.
With that we have reached the end of PAOLI interlocking. Tune in next time where I will cover the tower itself, both inside and out.