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Sunday, September 11, 2011


Seeing as how my 2009 PRR Main Line Survey has reached the Golden City of the PRR I thought it appropriate to reach back into my archives and post some photos on the famous PRR interlocking tower that still routes trains around the large yard and shop complex 24/7 as it has for the past 100 years.  I am talking about ALTO tower, but unfortunately I had not been intending that this post serve as a memorial to an icon tower which now faces closure later this fall.  While efforts are being made to preserve the tower, even if it does somehow manage not to fall down or catch fire , this living tribute to the PRR will be at best mounted and stuffed, the tracks it oversaw sterilized of character and rendered completely generic.

About 5 years ago I took a little trip there when Amtrak still ran two train services on the main line and it was possible to get out and back in the same day. This trip turned out to be very special because I was able to not only take pictures of ALTO tower on the outside, but also inside ALTO tower and after a sufficient waiting period I am free to put them up for public consumption.

Before we begin I should mention that the full set of photos from this trip can be found here

ALTO tower was rebuilt to its current configuration in 1915 (and possibly existed in some form for many years prior to that) in the typical PRR style of all-wooden main line towers with the trademark bay windows. Over the years CTC control of the entire Altoona terminal area was transfered to ALTO and in the 1970's the interlocking was somewhat rebuilt by the Penn Central. Because of the CTC ALTO survived as an active interlocking tower far longer than almost all its brethren and currently controls ANTIS, HOMER, ROSE, WORKS and SLOPE interlockings.

So here is ALTO tower from the front. It had been last painted in Conrail colors in the 1980's and at this point is looking somewhat shabby. In 2009 NS came by and provided a nice re-paint job in an overall flat gray which gave the false impression that ALTO had a long life ahead of it.

ALTO from the side showing the side bay extension that was added because of the need for a longer interlocking machine inside. Access to the tower is across the tracks, not from the road behind.  In the future the new ALTO interlocking will begin just west of the tower's current location and run to about where SLOPE currently sits.

From this rear view you can see a newer steel external stairway, fuel tank for either the heater or emergency generator and the old style relay cabinets for the signal gantry.

It's amazing some of the architectural details that went into these old towers.

ALTO interlocking is made up from two logical parts. There is the main interlocking controlled from the original 27 lever US&S electro pneumatic interlocking machine, and a smaller extension controlled from a partially independent 11 lever machine next to it. The PRR pedestal signals at the west end of the Altoona station platform are part of the extension, while the large signal bridge controls access into the interlocking proper.  A complete track chart of ALTO can be found in this large (30MB) pdf of Conrail interlocking diagrams.  ALTO is on page 23.

Here is a historic photo showing the Penn Central era configuration with PRR PL mast signals at the east end of the interlocking.  The 38L signal is displaying Slow Approach over the  reverse 31 switch towards a Clear indication on the 2L.  If this doesn't make sense, a 1985 head end video shows the track between the 32R and 2L being used as an additional helper pocket.  Regular movements from Track 2 to 3 were made over the 1 switch with an Approach Medium displayed on the 38L and a Medium Clear on the 4L.  When the east end was reconfigured in the Conrail era, this pocket concept was eliminated.

In the updated arrangement Amtrak train now waits to depart Altoona station on a Medium Clear aspect on the 38L pedestal signal for a diverging movement from 2tk to 3tk, while the 2L signal on the main bridge displays Clear. This is the point where #3 track begins and will remain until CP-CONPIT.  Also in this picture we see a pair of helpers waiting in the pocket and an eastbound freight train about to roll through on #1 track.

Closeup of the 38L signal displaying Medium Clear.  This advance part of ALTO will probably be eliminated allowing a straight through configuration for both tracks 1 and 2 with track 3 being extended through to CP-WORKS.

The famous ALTO signal gantry was installed during the Penn Central era. It holds the 2L, 6L and 8L signals.  It is likely that this mascot of the Altona railroading scene will also be rendered redundant despite its young age and robustness, unlike similar structures at HICK tower that were integrated into the new CP-503. 

ALTO tower is designed to facilitate helper movements and has a pocket track between 1 and 2 tracks that allow helpers to latch onto passing main line trains. Here a helper pair lay over in the pocket tack under the famous gantry.

The eastbound gantry is a very early design that really skimps on the raw materials, which were much more expensive back in the day. This gantry supports signals for #1 track and #0 track. In the foreground is the tower operator's car.  In contrast today it is far cheaper to build new signal structures in parallel than to reuse even sound existing ones due to the labor costs involved with splicing existing signals into new interlocking hardware.

Rear view of the 10R and 12R signals on the old gantry. SLOPE interlocking can be seen far in the background.

Moving inside the tower we find a very early model US&S Electro-Pneumatic machine. This offering predates any concept of Model so it is only known as an Electro-Pneumatic machine. The Pneumatic comes from the pneumatically powered points and not anything inside the interlocking itself. At the present day the 27 lever machine has 7 for signals (paired where possible), 9 for switched and 11 spare spaces.  Here we see levers 1 through 13. As was US&S practice odd levers are for points and even are for signals. Signal levers mostly have two positions to control a pair of signals, although at some point a few, like 4R, only have one. The lamps light either when a lever is free to be moved or is locked.

The east end extension is slightly newer and dated from what is described as a 1915 rebuild and holds levers 31 through 38 with 4 levers for signals, 2 for switches and 5 spare spaces.  This style of machine is newer than the other, but still represents an early incarnation of what would become the ubiquitous "Model 14" design.  Seen in towers built between 1910 and the mid 1920's other recent examples include North Philadelphia (closed 2005) and Q Tower in Sunnyside Yard (still open)

The Model Board was modernized sometime during the Conrail era with a plastic front, miniaturized lamps and label maker labels.  This is the east end showing the two main tracks, a controlled siding and a yard lead. The blue lamps on the arrows are traffic control indications. Traffic control is handled from the CTC machine. Also note that a turnout from 1tk to 2tk allowing access to 3tk has been removed in recent times due to the lack of need for a parallel ladder.

Center right portion of the model board. Some signals are marked "phantom". This means the signals are there logically, but not there in reality. This is an artifact of the second interlocking machine installed for the east end extension.

Central part of the model board showing the two signal gantries and ALTO tower. Here is the main trailing ladder track used by trains going to/from the yard and helpers.

Left side of the model board showing the extension of the ladder on #3 and #2 tracks.

Some of the signal rundown timers, cleaning supplies, blocking devices and in the background you can see the SLOPE interlocking CTC machine.

SLOPE was the first interlocking remoted to ALTO and is only about a half mile to the west. SLOPE terminates the '0' track and also provides a facing point crossover from #1 track to #2 track, an option that is not present in ALTO proper. The interlocking is controlled from what s described as a "Miniature Electric Machine" which although in the same unit lever panel configuration as a standard US&S CTC product, I do not believe it uses 504 pulse code control, instead probably implementing some sort of direct command setup to the remote interlocking.  SLOPE stands to be completely eliminated in the 2011 re-signaling project.

Operator's desk showing the computer which tells him or her what trains are approaching. Also there is still a paper block sheet which needs to be filled out. This tower used to report trains to 'C' tower, but its closure removed that requirement. To the operator's left is the CTC console that controls the rest of the Altoona terminal.

Here is the east half of the 504B code system CTC console showing ANTIS, HOMER and ROSE interlockings.  HOMER, ROSE and WORKS were placed in remote from ALTO during the early 1970's Penn Central era.  ANTIS was re-signaled and placed under remote control by Conrail in 1981. 

West side of the CTC machine showing HOMER, ROSE and WORKS interlocking.  These 1970's all-relay interlockings will also be re-signaled as part of the 2011 project with new signals as well as interlocking hardware.

Rear of the interlocking machine, lockers and doorway.

Rear of the interlocking machine and model board.

ALTO as seen from itself, with a train passing by.

Coal train making a diverging(?) move from 2tk to 2tk.

Fortunately thanks to its location in the Railfan capitol of the world, ALTO has been documented many times over, but the thought that future generations will never get to experience the unbroken expanse of position lights controlled from a operator in a tower that had been manned 24/7 for possibly over 100 years is distressing to say the least.

Next time we will continue our trip across Pennsylvania by heading up and over the Horseshoe Curve.

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