Pennsy and N&W Style PL Signals

RAILROAD SIGNALS of the U.S.

PRR POSITION LIGHT (PL) SIGNALS

BACKGROUND
Tombstone Signals - The Original PL signal
The PL Lamp Head
PL Signals
the Aspects
VARIATIONS in PL HEAD CONFIGURATIONS
Upper Head
Lower Head
POSITION LIGHT SIGNAL VARIATIONS
The Domino Signal
A Northumberland PA Duo
Small PL's - Dwarfs
Small PL's - Pedestals
SIGNAL LOCATIONS
Huntingdon PA
Lancaster PA
Mapleton PA
Norwood OH
OTHER PICTURES
Signal Bridge in Halethorpe MD
Former Signal Bridge in Halethorpe MD
Drawings / Technical

For Amtrak PCL signals, which used to be Pennsy PL signals, click here.
For a boatload of PL signals in Perryville MD, click here.
For a bunch of PL signals from Aberdeen MD and north, click here.

A Little Background

The Pennsylvania Railroad started experimenting with a radically new signal design in 1915 (see my timeline). This signal consisted of rows of yellow lights, in an attempt to simulate the position nature of semaphore signals.

The decision to find a new signal followed the start of electrification in 1913, once they found it was difficult to see semaphores thru the catenary wires (despite this problem, the New Haven stayed with semaphores).

The design of these new signals also coincides with the development of a pale yellow "fog penetrating" lens by Corning.

Both the Norfolk and Western Rwy and the Lehigh Valley RR used PL signals because of their affiliation with the Pennsy. The N&W however, started a colorization program in the mid 60's, deleting the center lamp altogether unlike the "red eye" signals found west of Harrisburg PA on Conrail.

Here are Pennsy related dates from my signal timeline:
1870's - The Pennsylvania RR, well known for a long list of "firsts", was among the first to use semaphore signals for interlocking.
1871 - Pennsylvania RR absorbs the Camden & Amboy, and block signal installation was completed between Jersey City and Philadelphia.
1882 - The Pennsy installs its first electro-pneumatic lower quadrant semaphores.
1884 - The Pennsy is the first to install an automatic block network utilizing electro-pneumatic lower quadrant semaphores between East Liberty and Wilkensburg PA - by the end of 1884, 65 were in service.
1906 - The first of the three aspect upper quadrant semaphores was installed on the Pennsylvania RR between W Philadelphia and Elwyn PA.
1906-1908 - Research by corning into lenses and colors, and they came up with the current green-yellow-red, replacing white-green-red.
1913 - The Pennsylvania RR starts electrification.
1914 - Perfection of a concentrated-filament lamp to provide color light signals a satisfactory sighting distance.
1915 - Dr. William Churchill of Corning Glass developed a pale yellow "fog-penetrating" glass, which the PRR then used in their PL signals.
1915 - The Pennsy introduces (experiments) with the first version of the PL (position light) signal and it is nick-named a "tombstone" signal because the top of the signal was round and the signal resembled an old tombstone…… also, later adopted on it's affiliates the N&W and LV.
1916 - The PRR and NYC finally change their rulebooks to reflect green being used for proceed instead of white.
1917 - They changes the shape of the "tombstone" signals slightly so they do not present as much wind loading as the older style… they also used "stepped" voltages of 11, 6, and 4 volts to adjust for day, twilight, and night (and these were manual adjustments made by the signal guys).
1918 - The PRR simplifies the design of their PL signals, eliminating one of the four "heads" for each aspect.
1921 - Pennsy's PL's started taking the shape and configuration were are accustomed to today.

If you are interested in a most complete history of the Pennsylvania and signaling, check out J. B. Calvert's page.

Early Position Light Signals
Tombstones

The original Position Light (PL) signal consisted of rows of four lamps, with one being common to all three aspects, as shown to the left. It appears from this drawing, that the central housing, nicknamed the "spider", is close in design to the ones used on current PL signals.

Below is the only photo I have been able to locate of the original tombstone signals. I don't remember which book it's from, but I found it through Google books (in fact, this and all of the drawings are from it).

Here are two charts of the signal aspects and their meanings:

The PL Lamp

The following diagram shows the principle behind the design of the PL-5 lamp. This is one of the few lamps that has a reflecting surface behind the lamp to (a) increase the brightness and (b) focus the light beam.

The design of the outer contoured lens is to reflect incoming light (from an engine, for instance) off center so it does not enter the innards. The tip is frosted to increase the effect. This lens is yellow in color, which optimizes light transmission through the fog, which explains why "real" fog lights on cars are the same color (not white like the "fog lights" on my Avalanche).

Behind the yellow lens is another reflecting lens for the incoming light which managed to make it through the outer lens.

Behind that is yet another "lens" to further reduce the effect of stray light entering the lamp off-axis. This lens is called a "phankill" unit, and is nothing more than a flat black painted honeycomb material. Being painted flat black, it will absorb light that strikes its surface. Although it will also absorb light from the bulb, the majority of light from the bulb will be parallel to the viewing axis (and honeycomb material), thereby passing through with little attenuation. (FYI - Older traffic lights use a honeycomb material on the exterior of the lens to make the signal directional, the deeper the material, the more directional the viewing angle is - More modern versions use a sophisticated optics system and a special focused / projector type reflector lamp, and are called PVL's, or Programmed Visibility Lamps)

Below my drawing is a cross section of an earlier version of this lamp.

PL Signals

The Pennsy, in 1918, simplified the Tombstone signal to pretty much the design that exists today on Amtrak and the Norfolk Southern, although Amtrak started the transition to colorized versions in 1988, eliminating the center lamp. Conrail in some locations substituted red lenses for the stop aspect (sans the middle lamp, also called the "pivot" lamp), keeping the center lamps for the other indications which are still all yellow.

Cover of the Long Island RR's monthly magazine, the Railroader, showing a training class on signals for the engineers
Notice on the left you have a high and dwarf PL, and on the right, a pedestal signal
Wouldn't you love to have those two classroom aides now?

A signal in Columbia PA, just south of Rt 30 along the Susquehanna River. This signal controls a siding where is runs into the mainline. Pictures taken SEP2003. Note that signal has not been colorized. The photo at the top of the page is also from this set.

the Aspects

Click Here for this in PDF format

PL Signal Upper Head Variations

Top head of a two head signal in Marysville PA. It appears that the background is not an original Pennsy background. The stop indication has had the yellow lenses replaced with red lenses.

Top head of a signal in Northumberland PA (the lower head is directly below).

A nicely restored Pennsy PL signal at the Railroad Museum of Pennsylvania in Strasburg, until you notice that they do not have the proper lenses in the lamps. The hoods also look to be a little on the short side.

PL Lower Head Variations

Lower heads seem to have much less consistency in there appearance than the upper head, when present. If more than one aspect was displayed, there was usually a round face with flat sides, as shown on the left directly below. On the picture to the right, the "round" face was used/retained, even though two of the three aspects are not present (not sure if they were ever there or not).

Much less common, is a full round background, as can be found north of Marysville PA in the second set of pictures. This set of pictures also illustrates a variance in standard PRR practice, where both signal heads are above the bridge structure. Usually, the bottom head would be in front of the bridge in between the two decks.

The diagonal lower head in the third set of pictures was the most commonly used variation when only one diagonal aspect was used. Sometimes an oblong background was used, but they were used mostly when a vertical aspect was used by itself.

On intermediate signals where a single lamp was used for the "stop and proceed" indication, no background is used, the lamp is naked.

A couple of standard lower heads, with the background sides cut off . The head on the right is the lower head of the Marysville signal above, the other one is in Northumberland PA.

Just north of Marysville PA is a signal bridge with three SB signals. This is one of the three, in which the lower head has a full round background. Not many of them around. On the right, another example of a full background on the bottom head is from Perryville MD - a freight coming down the Port Road from Harrisburg would see this signal.... Baltimore is to the right and Philly is to the left at this wye, with a hint of Perryville commuter station in the background.

Typical single aspect diagonal lower head without a background, in Columbia PA

Typical single aspect lower head with background in Mapleton PA.

A full PL signal, showing how half of the lower heads were installed, with a vertical background on only the one aspect. Why is this a full PL signal? The restrict aspect is only displayed on the lower head, hence, those positions are blanked out on the upper head, and the stop aspect is only displayed on the top head, that's why there are no horizontal signal lamps on the bottom head (the center lamp on the bottom head is used in conjunction with the horizontal lamps on the upper head for stop).

PL Signal Variations

Way Strange PL Signal

These two signals are located in Northumberland PA, about 50 miles north of Harrisburg PA. They are at the entrance to the Northumberland yard, after you cross the Susquehanna River from Sunbury. These are the only signals like this in operation that I am aware of.

Domino Signals

Domino signals were created because of the limited sight distance afforded by the many overpasses in approaching the Chicago Union station. According to a recent discussion on the Yahoo Pennsy Signaling group, they were also found in a couple of tight clearance places in New Jersey. The signals are basically the same as a standard PL, but the top and bottom lamps in the middle are on shorter pipes, thereby making the top and bottom row of signals to be in a straight line, the same as the middle row - the normal spacing is 18" center to center.

For more pictures, click here.

An excellent shot of Amtrak #587, heading out of Chicago's Union Station, sometime in the mid 70's... notice the Domino signals on the bridge in the background. There's also a lot of other good details in this shot... the double slip switches, the PL dwarf to the left of 587, color light dwarfs over by the Penn Central Geep (altho it looks like a bunch of dwarf signals stacked next to each other next to the geep), and it looks like the switch motors are electro-pneumatic.....
Photo courtesy Tim Vermande, Thanks Tim!

Dwarf PL's

Dwarf signals use 4" lenses, and are frosted white to reduce their effective range so they won't be confused with high signals. Lunar white was used some time later.

These signals come in both "right-hand" and "left-hand" versions, where the rounded side can be on either the left or right side. Although I guess the Pennsy could have placed these signals in a square housing, they placed them in "rounded corner" housings. The vertical aspect was originally on the left, and later, as the railroad wanted to use them on tracks with smaller spacing's, they changed the housing around 1930.

Interestingly, the Pennsy PL dwarf has seen widespread use all over the world. For example, the Baltimore Light Rail System uses them for route indicators. The Canadian Pacific uses them in at least one yard as shove signals. Pictures of them can be found on many of the sites covering railroads of other countries.

Typical dwarf PL, this one is at the Strasburg RR.

Dwarf signals can be mounted on the ground (above), on poles, and on signal bridges (below). Some transit systems, like the Baltimore Light Rail system, use them as route indicators. This dwarf is mounted on a pole about 6ft high, and is used at the wye in Perryville MD. The Pennsy commonly used dwarf signals in this application, where trains were coming on or off a main line and operated at slow speeds.

In a different application, CP Rail uses dwarf PL's at Pigs Eye yard St Paul MN as a shove signal, indicating to the engineer when the rear of a train is at a certain point at the tail (south) end of the yard.

Pedestal PL's

The other "small form" the PL signal can take is known as a "pedestal" signal. This type of signal places two dwarf signals in one housing, one atop the other. Through a discussion on the Yahoo Railway Signaling group, it is a medium speed signal, limiting speed to 40MPH, even though it can display clear block" (which on the main line with a high signal, would allow the train to go at the posted speed). On the north side of the Wilmington (DE) station, the Pennsy used pedestals on the overhead signal bridge, maybe because of clearance issues with a larger full size head.

The left photo is a pedestal signal in Newark De, on the approach to the NEC.
The second photo of a pedestal and dwarf is at the Baltimore Amtrak station from approx 1972.
Third photo is an unused pedestal in Huntingdon PA, more info below.
Photo on the right is the only place I know of pedestals being used as a high signal, north of the Wilmington DE Amtrak station, LED's used in the left one.

If anyone has any pictures of the "red eye" pedestals, they would most certainly be appreciated.

- Signal Pictures -

Many "pure" Pennsy PL signals can be still found all over the place. Here is a small sampling.....

Huntingdon PA

This first set of signals is located on the east side of Huntingdon. Huntingdon is about 28 miles east of Altoona via us22, and about 15 miles west of Mt Union, the northern end of the East Broad Top narrow gauge steam railroad. Also in town is the (closed) HUNT tower. The tower used to be open for visitors several years ago, but when there in 2008, that was no longer the case... darn.

The signals, switches, and interlocking in Huntingdon used to be controlled from here, HUNT tower.

This second set of signals is located on the west side of Huntingdon. Access to these signals is very easy through the park, which also contains the H&BTM bridge shown above. On the bottom row is a lone pedestal signal for controlling the ex Huntingdon and Broad Top Mountain RR interchange, which hasn't been used since the late 90's.

Lancaster PA

Located on the west side of the station in Lancaster is this signal bridge for EB trains. Lancaster is about 25 miles to the east of Harrisburg. If you're not from around these here parts, Lancaster is pronounced with the emphasis on the first syllable as "lang", and then a quick "ke-ster" to follow

Mapleton PA

Mapleton is the next set of signals west of Mt Union, about two miles away. It is off US22, via PA655/Main St from the west, or PA2020/Oriskany St from the east, and then by taking Bridge St over the river, and a right onto Railroad St. Two of the photos show the conical lenses pretty well. The signals are approach lit.

Norwood OH

From Nicholas Longshore comes this set of photos at the Penn/Oakley/Ridge wye in Norwood OH, where one of the traditional US&S signal heads was replaced with one made by Safetran. It appears that almost everything is different except for the outer lens and hoods. The housings are of cast aluminum, compared to US&S's version which is cast iron. From the front of the signal, it would be almost impossible to tell the difference. Great detail shots Nick, Thanks!

- Other Pictures -

Pictures from a trip Michael Watnosky and I took in April of 2008 to Wilmington DE are here.
And pictures of the PL signals in Perryville MD are here. (over 200 pix on the page)

A link to pictures on the Library of Congress website for a few PL related items:
B&P Tower in Baltimore before being moved, good shots of inside: click here
ALTO Tower in Altoona PA: click here
Union Tower in Baltimore: click here

Signal Bridge in Halethorpe (Baltimore) MD

These signals are located in Halethorpe MD, adjacent to the MARC commuter stop, and demonstrate how Amtrak has modified the signals to colorize them.