The relevant track charts for this segment can be found here.
Beginning at Greensburg it is worthwhile mentioning an interesting feature of the right of way that important to the signaling in the area. You may have noticed in part 3.2 that SW tower at Southwest Junction had a western section where the 4-track right of way shrank to three tracks for a pair of tunnels. I mentioned that past CP-CONPIT the main line took off overland across a plateau to reach Pittsburgh directly instead of following the Conemaugh River. This resulted in a steeper grade profile as well as a number of bottlenecks in the Greensburg area in the form of tunnels. The first was located directly east of the station and was eliminated in the 1890's, the second set of tunnels hung around a lot longer and remained an operational headache.
Known as the Radebaugh tunnels after the community west of Greensburgh (which had its own tunnel) the first was built in 1852 as part of the original Main Line project and nearly derailed the entire enterprise as the cost and delays of tunneling began to give the Philadelphia area investors cold feet. The original tunnel was very tight and built on a curvy alignment through the local drainage divide between the Conemaugh and Monongahela rivers. In the 1890's a new, larger tunnel was built on a more direct alignment, at first replacing the original tunnel until traffic levels pressed the 1850's bore back into service to carry a third main track. You can see the two tunnel alignments on this Wiki Map.
http://www.wikimapia.org/#lat=40.311390 ... =Radebaugh
Still, three tunnel tracks on a four track line a bottleneck makes, but adding a 4th track or simply removing the tunnel never became a priority for the PRR so they did the best they could with interlocking design. Directly on each side of the new 1890's tunnel the 3 tracks shrank to 2 via a parallel shift layout with freight track 1 having the forced diverge at each. Track #4, also designated for freight, used the pimple alignment of the 1850's tunnel allowing the designated passenger tracks 2 and 3 the straight shot through.
In 1965 the waning PRR showed some of its old magic when new tunnel was daylighted in a project where the overburden was first removed and then in the space of 11 hours the tunnel roof was blasted and track re-laid with the RoW being widened over time. Track #4 remained in use through the old tunnel on the alternate alignment until the deluge from Hurricane Agnes collapsed it in 1972. The 1980 CTC project under Conrail did the rest permanently making the line two-tracks.
Anyway as I said all this was relevant to signaling as both SW tower east of the tunnels and RG tower, west of the tunnels, were built to deal with the bottleneck. Here we see the location of the new tunnel now just an open cut. In the right of the picture there is an interesting signal facing away from us for traffic on the branch line which is labeled R08. This is a distant signal to the upcoming interlocking and a vestage of the old PRR Manual Block system.
In this view taken in 2004 we see R08 in its original configuration as a PRR Position Light. This signal could display, Approach Medium, Approach and Caution. Approach Medium would display when a train coming off the branch line was had a proceed indication like Medium Clear and Approach would display if the interlocking was showing a Stop indication. Both would show that the track circuited approach block was clear, however if it was not the signal would display a Caution signal which on a PRR PL is \ over a marker light as shown in this photo.
Under NORAC the old PRR signal aspect was joined by other fixed distant styles such as the traditional yellow semaphore held at / with an (A) plate and a single yellow lamp also with an (A) plate. As the owner of the interlocking is responsible for maintaining the distant NS eventually got fed up with supporting a full PRR PL at R08 and "upgraded" it with the single yellow lamp variety sometime around 2006. Here is a front view of the new Approach Restricting signal from Railpictures.net. Not quite the same is it.
Ok, finally moving on we get to CP-RADE, formerly RG (RadebauGh) interlocking. Built in 1890 as part of the tunnel project RG complimented its neighbor SW and there were actually no intermediate signals between the two. The two towers had to work together to signal trains on the bi-directional tunnel tracks. When built in 1890 electricity was still new-fangled so there wasn't much of a power grid around to power the electro-pneumatic interlocking machine, air operated points and track circuits so RG was actually build with a railroad owned and operated power plant behind it. Pretty amazing that back in the day railroads had to act as both telecom outfits and power companies. Talk about vertical integration! Here is the original diagram of RG, you can see the power plant behind the tower.
Regrettably no trace of RG tower of the power plant remain today, but unlike SW interlocking, RG interlocking is still around in the form of CP-RADE. CP-RADE lost its westbound PRR signal gantry shortly after Norfolk Southern took over Conrail in 1999. The C&S department still had a commitment to target type signals, but was forced to buy from the Safetran catalogue instead of US&S so we have the Safetran style modular lamps with a circular mounting.
The main signal were also re-located a few hundred feet east to provide better visibility for approaching trains. The branch line signal remained at the same location. Note supports for the old PL gantry.
Points were left pneumatic. The switch to the Southwestern Pennsylvania Railroad owned branchline is good for 30mph movements.
The airline looks freshly painted next to the relay hut.
The eastbound signal remains a PRR PL.
The 3284 automatic distant to CP-RADE was also replaced around 2000 and I remember finding photos alerting me to the loss at that time. Signals next to a grade crossing of course creates another popular railfan location. BTW look at the grade profile.
The 3304 automatics were replaced in the Conrail era.
The surviving PRR gantry holding automatic signal 3326 used to be the westbound home signal of CP Interlocking at Larimer, PA. This was another mixing bowl interlocking where the passenger traffic was shifted to tracks 4 and 3 and the freight to tracks 1 and 2. This was due to the upcoming Pitcarin Yard and the desire not to have trains crawling into the yard foul the interlocking plant for passenger trains needing to cross over. For some reason this signal supports 4-block signaling westbound despite a standard sized block length.
Automatic signal 3346 is the distant to CP-TRAFF.
CP-TRAFF in Trafford, PA, formerly SZ interlocking lost its westbound PRR gantry in the 1995 clearance project. The large relay cabin is located about where the tower used to be. The line coming in from the left is a local industrial track.
The eastbound signals at CP-TRAFF were upgraded right around the NS takeover as evidenced by the Safetran style target lights. Formerly the signals out of the yard were PRR dwarf signals allowing only 15mph movements. The new cantilever signals allow 30mph movements. On the main tracks track 1 was governed by a strange upper diagonally braced cantilever with a PRR PL on the end. Track #1 used a mast. The two cantilevers at CP-TRAFF appear to be from different manufacturers possibly indicating the main signals were replaced as an after thought.
Back to back with CP-TRAFF is CP-WING in Wilmerding, Pa. Formerly WG Interlocking it governs the west end of Pitcarin Yard, which is now a large regional intermodal terminal. Originally WG interlocking was mostly concerned with routing freight trains between the main lie and the Port Perry branch which bypassed downtown Pittsburgh via two large bridges across the Monongahela and Ohio Rivers. Like SZ the interlocking was not designed to mix trains on the passenger tracks with the freight tracks. Here we see the westbound mast signals and a COFC intermodal train on track 1. Out of frame to the left is George Westinghouse's original Air Brake factory.
Again air operated point machines. Note one of the CP value units is almost completely buried in ballast.
The intermodal train is actually coming off of the Port Perry Branch.
Here is the 3-track eastbound PRR signal bridge at CP-WING. Note the Port Perry Branch signal has the Approach Medium indication due to the back-to-back interlocking arrangement.
Now these next two signals were installed with the 2003 extension of Pittsburgh's East Busway which was built on the unused portion of the former PRR right of way. If building a busway on the former PRR Main Line doesn't boil your britches, to add insult to injury Norfolk Southern installed more Safetran style target signals in home town of the Union Switch and Signal company, Swissvale, PA!!
This is the MP 342 automatic using the new style numbering system and eb distant to CP-WING.
I should also mention that this was the former location of R Interlocking that was another mixing bowl in the manner of CP interlocking to re-align traffic around Pitcarin yard. Like CP it was removed when traffic levels and CTC made them redundant.
Here is the MP 345 signal with the ::shudders:: busway on the left. This is the wb distant to CP-HOME.
CP-HOME named for Homewood, PA was originally CM interlocking and provided a connection to the eastbound Conemaugh Line, via the Brilliant Branch, which was unavailable on the route through downtown Pittsburgh. This also served as another bypass of the downtown terminal area in a similar fashion to the Port Perry Branch. The westbound signals are mounted on a pedestrian overpass.
The blurry dot of light on the right is a pot signal governing a small industrial spur.
CP-HOME continues along the wye track connection to the left to another series of signals and power switch at the north apex. Note the air pipes.
Nicely painted eastbound mast signals. The west apex of the wye track is not interlocked and instead just has a hand operated, electric locked switch. This is where my trainset will be turned for the return trip the next morning. After discharging passengers in Pittsburgh the crew will make a backup move through CP-HOME, proceed on signal indication to the north apex then reverse all the way back to the station.
NS installed this new cantilever around 2005 replacing a pair of PRR PL masts that had probably been installed in the late 80's with phase 1 of the Busway. Note that both westbound signals can at best display Approach Medium. This was a speed control measure for the sharp curve at Pittsburgh Penn Station.
A short distance from that signal on track 2 is CP-BLOOM. This interlocking was installed as a connection to the former B&O line through the city. The primary use of this line is my Amtrak's Capitol Limited as it switches from the PRR alignment to the B&O alignment for the trip to Washington, DC. This is the westbound mast signal and has a Safetran upper head and a US&S lower head.
A little wider angle. You can see the B&O CPL signal at FIELD interlockin on the P&W Sub off to the left. The best signal the eastbound signal on #2 track can display is again, Approach Medium.
Signal for the connector track. Again Safetran upper head, US&S lower.
Single set of electric points.
Eastbound signal and relay hut for CP-BLOOM.
We are crossing over at CP-EAST PITT to access the station track which serves track 1 only. This marks the end of Cab Signaling westward. Is it just me or is the PRR PL mast in the middle of the parking lot somewhat hilarious? Users of that lot had better watch how far they pull up or their vehicles might be missing bits when they return.
A little less grainy photo of the crossover at CP-EAST PITT. For the third time the best signal you can get at CP-EAST PITT westbound is Approach Medium and for trains making a straight move on track #2 it will be Approach Slow. The reason for this is that the sharp curve within the Pittsburgh station was rated for 15mph and as a result CP-WEST PITT only had 15mph PRR dwarf signals.
Eastbound masts at CP-EAST PITT. These are a very early model of Safetran position light and possibly one of the first large scale uses of the US&S alternative PRR PL.
PITT tower had the largest US&S Model 14 machine ever installed with over 350 levers. Today CP-PITT only controls a handful of switches on track 1 at the east end of the old PRR Station in downtown Pittsburgh. Here we see the westbound mast signal for CP-PITT in service on track 1 only. PITT Tower can be seen in the background to the left. Due to the 15mph curve and the dwarf home signals at CP-WEST PITT the best the 2W signal at CP-PITT can display is Approach Slow (/ over /). When CP-WEST PITT and its Slow speed signals were removed a few years ago NS decided not to alter CP-PITT or CP-EAST PITT in the continued interest of speed control at the sharp curve. The switch in the foreground is the east end of the 3000 foot controlled siding / station track.
Here we see a tubular cantilever structure as previously seen at CP-WORKS. I assume this went in in 1980, but it thought these types of cantilevers date from the Penn Central era so I just don't know. The signal to the left governs what used to be a station siding track and can display Approach Medium for diverging moves at CP-EAST PITT.
In the final picture of this long journey taken from the train we see on the right two stub end station tracks where this trainset will spend the night along side some various private cars. To the left is what used to be a short 3000 foot siding that was used by helper sets and even had a small crew base. It is also signed as a station track.
Of course if we go back in time to 2004 CP-WEST PITT was still there along with its PRR pot signals. The interlocking was in service on all tracks, but signal on track 2 did not protect any switches.
CP-WEST PITT with the signal on track 1 pulled up for Amtrak's Three Rivers...which itself was discontinued in 2005.
Here is the dwarf signal coming off the station/siding track. Note the lack of a lamp to display Slow Approach aspects. There were Pedestal exit signals located at the other end of the interlocking so the dwarf signal would go right from Restricting to Slow Clear. I got quite a chill taking these pictures as you can see the platform is covered in ice.
When CP-WEST PITT was in service the track speed of the 15mph curve was in essence enforced by the Slow Speed dwarf signals at the interlocking. Eastbound trains entering the interlocking were governed by pot signals placed on the ends of the Allegheny River Bridge trusses while westbound trains exiting the interlocking would pass a set of PRR Pedistal type exit signals in front of same. Across the river a pair of single-direction intermediate gantry signals served as "right' direction distants to CP-PENN and CP-WEST PITT on their respective tracks. When NS eliminated CP-WEST PITT they also eliminated the exit signals and the single direction intermediates by replacing them with a part of bi-directional Darth Vader masts with two full heads in each direction. The yellow lamp means these intermediate signals can display Approach Slow (Y/Y) for slow speed routes at the next interlocking. Here we see the 3532W signal which is using the Conrail style numbering practice. Note the Milepost 0 marker at the start of the bridge.
Actually only the track 2 mast has two full heads in each direction. The 3531E signal only supports Approach Medium (Y/G) and not Approach Slow because the slow speed condition exists at CP-EAST PITT when it displays SLOW APPROACH for a stop at CP-BLOOM. Because of the intervening CP-PITT on track #1 can display Approach Slow for this condition the 3531E only needs to display Approach Medium for either a Slow Approach or Stop indication at CP-EAST PITT
To suitably we end at trip at Milepost Zero where Lines East meet Lines West. In a nice nod to Conrail the old CP-WEST PITT sign has been left in place at the western end of its old interlocking limits, 353 miles from the end of the platform at Suburban Station, Philadelphia.