RAILROAD SIGNALS of the U.S.
B&O COLOR
POSITION LIGHT (CPL) SIGNALS
FOR STARTERS
Background
The
Mechanics of the CPL Signal
The
CPL Lamp Assembly
CPL
Primer
the Aspects
Catalog Drawings
Michael Watnoski’s Primer on CPL’s
SIGNAL
VARIATIONS
Main Head Variations
Marker Lamp Variations
Mounting
Variations
Dwarf CPL’s
SIGNAL PICTURES
Gaithersburg MD
Baltimore MD - Westport
Baltimore MD - Under I95
Baltimore MD - Ridgely St
Baltimore MD - Below Bush St 1
Baltimore MD - Below Bush St 2
Baltimore MD - Washington Blvd
OTHER PICTURES
For CPL and PL signals in Perryville MD, click
here.
For CPL and PL signals from Aberdeen MD north, click here.
CPL, or Color Position Light signals were exclusive
to the Baltimore and Ohio Railroad, and its affiliates. You could find
them anywhere the B&O went. However, now that all of the former
B&O lines are part of CSX, they have been accelerating their efforts to
replace the CPL's with modern 3 color light signals everywhere (yuk).
As with the Pennsy Position Light signals, the B&O Color Position Light signals were an attempt by the designer to simulate, or mimic the position capability of an upper quadrant semaphore signal. But, in contrast to the Pennsy signals, the B&O decided to use color in addition to position for their aspects. This provided a margin of safety in the event one of the two lamps was out.
Other railroads using CPL's are the Staten
Island Rapid Transit (SIRT, now part of the MTA), the former B&O Chicago
Terminal, and the former Chicago and Alton. Dwarf CPL's were also chosen
to be used in and out of Union Station in Washington DC, although they appear
on signal bridges above the tracks.
The first installation of CPL’s on the B&O was between Deshler and Hamlet OH. In December of 1924, the B&O announced that it had ordered 77 sets of CPL’s for the Staten Island Rapid Transit, and they are still in use today despite an announcement several years ago that they were going to replace them.
CPL dwarf signals also enjoy being the
only dwarfs which, if so outfitted, can display ALL of the aspects of a high
signal. The only one I ever saw so configured was at the B&O Railroad
Museum in Baltimore. However, I don't know if the signal before it came
to the museum was originally in this form, or if it was put together just for
display. Since the snow cave-in of 2003, the signal has not been on
display because the museum has decided not to use the outside wall for
displaying much of anything.
A fellow by the name of Frank Patenall designed the signals for the B&O around 1925. Patenall came to America in 1885, and worked for US&S before coming to the B&O in 1891. Some sources state that he developed the CPL signal concurrent with the development of the Pennsy’s PL signal, while others say he watched the development of the PL, and then “improved” on it by incorporating color to make it a “safer” signal. BTW, Pennsy installed its first Tombstone PL signals in 1915, so the latter statement may be true. Patenall was also the developer of approach lighting according to Brian Solomon in his book, "Railroad Signaling".
The signal was originally designed to display 14 aspects, but the current CSX rulebook contains 17 of them (it's interesting to note that 10 of them are green variations). Although the signal is capable of displaying 29 aspects (including flashing indications), many would be impractical, such as a slow speed stop, or modifications to the restricting aspect, they just don't make any sense. This is one reason why flashing is used to modify and upgrade a signals indication.
At first, the CPL signal may seem
confusing, but after reading the principles behind it, it’s fairly straightforward
in its interpretation…. There is a system!
The signals were originally manufactured by Hall, but later GRS and US&S made the signals, with the majority of them being made by US&S. The most popular designation for the dwarf CPL is US&S type VA. The full size signal is type “G”, which is why it’s confusing to refer to color light signals as type “G” (for the three color “tri-light” signals in a round background).
The Mechanics of the CPL Signal
The main CPL signal "head"
consists of a number of individual lamp assemblies mounted to a circular
background 3’-4" in diameter. There could be anywhere from one to as
many as four aspects displayed on the main part of the signal. The pictures below
illustrate some of the
possibilities.
The background is mounted to the mast with two heavy duty steel straps and U-bolts. The background itself is stamped from a piece of 1/4” thick steel, and has a 1 3/4” lip all the way around to strengthen the assembly, since the lamps mount to the background. The background has eight 7-5/16” holes stamped in it to allow mounting of the lamp assemblies, three 3/8” holes for each lamp assembly for mounting, and a 11/16" diameter hole above the lamp for sighting/aiming. There are eight (8) 7/16" holes for mounting to the brackets with 3/8" bolts. The two photos below show the lip and the lamp mounting hole.
Mounted to the backside of the background
is a junction box, where the cables from the relay cabinet terminate, and
individual wires go out to the lamp assemblies. On some older
installations, a separate transformer was used for each lamp pair, and they
were mounted in the junction box. The
transformers were used to step down the 120VAC to 10-12 volts. Because the 120VAC is mixed in with the low
voltage, they eventually decided to remove them from the junction box
altogether (probably for safety reasons), but also because it was more
expensive to provide a separate transformer for each indication (pure
speculation, though).
A GRS junction box, and the mounting holes for it viewed from
the front.
All of this stuff is mounted to a 5" outside diameter mast, up to 20 feet high. If the signal needs to be mounted higher, a 6" pole is used.
Unused positions are blanked by a 10-1/2" diameter plate, 1/16" thick and held into place by two or three screws, something on the order of #10's.
Most CPL signals also had what are known
as marker lamps located above and/or
below the main signal head. Very few CPL signals consisted just of a main
signal head, most had at least one marker lamp. If it was a high signal,
the sole white marker lamp was usually directly above, so the signal could
display a clear
aspect (rule 281), upgrading the
signal from a slow speed signal….. Without the marker lamp, the green
indication was slow-approach slow
A fully populated CPL would contain
fourteen (14) lamp assemblies, two lamps for each aspect on the main head:
green, yellow, red, and lunar; two (2) yellow markers to the right; and four (4) white
markers to the left and center. Very, very few CPL's have a full
compliment of 14 lamps. The only one around
used to be in Deshler OH, but was replaced with a color light signal around
2006. Baltimore recently (~2008) added a full CPL to the list, and we also
have an almost full signal a little further south, with only the restricting
aspect missing.
According to B&O drawings, the
majority of CPL signals placed on a single mast, were set at 17 feet above the base
of the rail. Marker lamps are placed 7
feet above and below the center of the main head, and offset from the pole by 3’-4”. In some installations which required more
height for visibility, the main head was 30 feet off the rail, with the markers still
being offset by 7 feet. The signal mast
was generally set about 13’-7” from the centerline of the track.
Bracket posts were set up so the base of the bracket was 23’-4” above the rail base, and the spacing between the two signals was 10 feet. The mast was placed 10 feet from the center of the track.
The lamp assemblies used on a CPL signal are pretty simple affairs. A single bulb, is focused by an inner colored fresnel lens, and an 8-3/4" (basically clear) outer lens. The outer lens for the white marker lamps are sometimes sand blasted on the inside . There is no reflector, which prevents false indications.
As seen below in the middle photo, the lamp assembly is mounted to the main head with three bolts, and uses springs to maintain their spacing from the background. By adjusting the nuts from the back side of the signal, the lamp could be aimed. Signal maintainers could look through an additional hole in the background for aiming purposes (above photo showing the cutout), viewing through a tang on the lamp assembly. The tang has a hole in it for aiming the lamp, which is clearly visible in the left photo below. The nuts used for adjusting the lamp, in later years, used ones with a nylon insert which did not require the use of a lockwasher.
While CPL signals may seem a little intimidating at first, due to the number of lamps associated with it, the system is quite systematic, and simple to interpret once the "secrets" are known......
The first thing to know is that the main signal head can display clear (green), approach (yellow), stop (red), and restricting (lunar white), but they are ALL slow speed indications without using the marker lamps to modify the indication (so OK, STOP is not a speed :-) to a higher speed.
If any three of the lower marker lamps are lit, the signal is upgraded to a medium speed signal, telling the engineer he can pass THIS signal at medium speed.
If any of the lamps on the top are lit, it is upgraded to a high speed signal for the block it controls, and he can pass THIS signal at normal speed: the maximum allowed by the timetable, rulebook, or indication. The photo below is showing a clear signal (rule 281).
If either of the two left hand white markers are lit, then the engineer needs to pass the NEXT signal at medium speed.
If either of the two yellow markers on the right are lit, he needs to pass the NEXT signal at slow speed.
CSX also uses flashing to upgrade the signal
in the following cases:
If the top left marker is flashing, the signal is upgraded
from approach medium (rule 282) to
approach limited. (rule 281B)
If the bottom center marker flashes, the signal goes from a
medium clear (rule 283) to a limited
clear (rule 281C) speed signal.
If the green lamps are flashing, the signal is upgraded from
slow approach slow (rule 287A, formerly rule
287), to slow clear (rule 287).
Current CSX speeds are below in Michael's section.
Michael Watnoski's
Primer
with help from
John V Engleman
B&O Color Position Light signals, CPL's, are the most complete signal system used today. This system is intuitive once you know the pattern. It also conveys more information than other signal systems. At the bottom of the page, is a drawing showing the components of a fully loaded CPL signal.
Another unusual feature of this signaling system, is that CPL dwarf signals are capable of displaying all the aspects of a high signal, not just slow speed aspects as most other systems.
Speeds referred to in the CSX rulebook, which this discussion is based on, are as follows: Limited - 45mph, Medium - 30mph, and Slow - 20mph. Some of you may raise an eyebrow at the slow speed. Yes, it was changed from 15!
A near complete CPL signal in south Baltimore
The main head displays the track occupancy for the selected route. The B&O only used a two block system. If the next two blocks beyond the signal were were clear (not occupied), the main head displayed a "high green" for "proceed". When the second block was occupied, the head displayed yellow for "approach", preparing to stop at the next signal. Trains exceeding medium speed were required to slow to that speed. If the block ahead of you was occupied, the signal displayed red for stop.
If the signal was an automatic, having a
number board, then this was regarded as stop and
proceed in the B&O days, and is now (under CSX), a
restricted proceed.
Stop and proceed allowed the train to move,
after stopping, at restricted speed (not exceeding 15 mph), prepared to stop
within half the distance of sight, while watching for stopped trains, broken
rail, or misaligned switches. If the route is set for an un-signaled track, the
restricting aspect, left diagonal lunar white lights, is used. This requires
the train to travel at restricted speed, as above.
The other six lights, or marker
lamps, refer to the speed rating of the route being taken immediately beyond the
signal and at the next signal.
Any light in the row above the main head indicates that route is going to be the main or high speed route beyond this signal. This allows the train to proceed at track speed, as posted in the employee timetable for the territory, on green signals.
The left and middle markers are white, the right marker is yellow.
There are two yellow aspects with a marker, and one red..... all use the middle marker.
Rule C-285 is approach, preparing to stop at the next signal. Rule C-286 is medium approach.... medium speed thru turnouts, etc, then proceed prepared to stop at the next signal.
The red aspect with a marker is rule C-291, restricted proceed, which the indication is the same for a restricting aspect - proceed at restricted speed. It has two variations, as shown to the left. Many of you may be familiar with this aspect being called stop and proceed. John adds, "during the gas shortage of the early to mid 70's, the B&O needed a way to to reduce costs, so they changed the rule to allow trains to keep rolling, looking for trains or problems ahead at no more than restricted speed".
Without any light above or below
the main head, the train is going thru switches at slow speed, and must limit
speed to 15 mph until the entire train is over the switches.
Obviously, there are three rules without markers lamps, and fall low in priority
except for red, which is "at the
bottom":
1) green
for rule C-287A, slow-approach slow
2) yellow, rule C-288,
slow-approach
3) red for rule C-292,
which is stop
Rules 287A and 288 fall next to each other in priority, the only difference being 287A specifies going at slow speed to approach the next signal, while 288 says to prepare to stop at the next signal, but does not give a speed once thru the turnout. Both mandate going at slow speed thru the turnout.
If
lit, the row of markers below the main head indicates that train will be routed
over switches at medium speed. The train must reduce to
medium speed, 30 mph, until all of it is passed through the switches,
then it can proceed at the track speed set by the signal. This is the typical
indication when changing tracks at a crossover.
Use of the lower markers specifies two
speeds for the train. One is the speed thru the turnout, which as stated above,
is medium speed. The other speed referenced is the speed of the
train tha
t
is authorized once the entire train has cleared the turnout. The speeds show up
in the name of the aspect, such as: medium-approach
slow or medium-approach medium.
The left marker signifies medium speed, the right marker
slow, and the middle marker is unspecified (the rule just says "then
proceed".
As above for the upper markers, the left and middle markers are white, the right marker is yellow.
CSX employs three flashing aspects, rules C-281B, approach limited; C-281C, limited clear; and C-287, slow clear. The first two had flashing markers, 287 used a flashing green aspect without any markers. It's interesting to note, if you look at the old versus the new rulebooks, that the B&O did not employ flashing aspects.
CSX also slipped a new aspect in the books with the flashing green of rule C-287 (slow clear). The solid green aspect that was formerly rule C-287, slow-approach slow, is now rule C-287A.
The two rules to the left, C281B (approach limited) and C281C (limited clear), could employ one of two methods to indicate the aspect. One option is to use a flashing marker (without the yellow triangle), and the other is to use a steady marker, with a yellow triangle sign.
Rule 281B was previously rule C-282 under the B&O, and what is now 282, was 282A. It's all very confusing!
This Drawing shows the major components of a full size B&O CPL signal. As seen in the photos above, if left and/or right marker lamps are used, there are also two pieces of angle iron used to stabilize each marker, going from the marker to the pole, in addition to the cross pieces shown above. A single 5" pole is used up to a height of 20 feet, above that, the pole starts out as a 6" pole at the bottom, and then reduces to 5". Refer to the US&S drawings on another page.
John Engleman formerly worked for the B&O as an engineer (also for the Pennsy for a while prior to that, and was qualified on both). His inputs have been invaluable in navigating thru some of the signal "urban legends" (and has some good stories to boot!).
Graphics and Pictures by Todd Sestero
Click Here for this in PDF format
the CPL pages from a 1935 US&S catalog.
Other CPL and CPL related Info Pages
http://www.alkrug.vcn.com/rrfacts/signals/ColorPosition/sigrules_BO.htm
Good CPL info by A A Krug
http://www.alkrug.vcn.com/rrfacts/signals/signals.htm
Additional signal info by A A Krug
http://www.cg-tower.com/cpl/
Good CPL signal info by Eric
http://www.navpooh.com/sigpics.html
Good CPL signal info by Mike
http://mtnsub.org/features/cpl.html
Good stuff on the B&O way out Western Maryland way by
Markolf
Gudjons
B&O Color Position Light Signal
http://www.jdtower.org/History.htm
http://www.trainweb.org/oldmainline/oml7a.htm
http://en.wikipedia.org/wiki/North_American_railroad_signals
http://www.borhs.org/Archives/cplcontent.html
Drawings for model railroaders by Michael Watnoski
The pictures below show variations in the indications the main CPL head can display.
CPL signals with only one marker, usually giving the highest speed available.
Two marker lamps.... Left is south of Bush St, right is at
Ridgely St, Baltimore.
Three markers, on the bracket post shown below for 6 markers.
Four markers on a signal bridge in Baltimore, slightly west of
Baileys wye at Ridgely St for NB traffic.... In the middle is one at the Dorsey
MARC station for SB traffic to DC showing approach, and finally on the right, a CPL on the north
point of Baileys Wye for SB traffic to DC displaying a medium clear.
Five marker lamps.... almost full.... The one on the
left is south of Bush St. in Baltimore for NB trains, the one on the right is
almost directly across the mainline at the same location for SB trains
A three marker CPL and a six marker CPL share this bracket
post installation south of Bush St in Baltimore for NB traffic, and a little
north of there, a few hundred feet from Bush St, is a "brand new" full CPL.
CPL signals can be mounted in a variety of ways. They can be mast, or pole mounted, they can be mounted on signal bridges, and they can be mounted on bracket posts. Unlike Pennsy PL signals, I have yet to see a CPL signal mounted on top of a relay or equipment case.
A typical B&O signal bridge, located off of Bailey's Wye to
the south, in Baltimore.
CPL signals on a cantilever bridge. The two on the left
are at the south end of Winans yard in Baltimore, and have been replaced by
colorlights. The right two photos are courtesy Eric Davis.
On the left is a traditional B&O mast mounted signal, on the
right is one mounted on a newer aluminum mast.
Typical bracket post installation at the south end of Winans
yard / Baltimore.
Dwarf CPL signals are normally mounted at ground level, or close to ground level. There are a few exceptions, the most notable one is probably the use of dwarf signals in the northern approach to Union Station in Washington DC, where they decided to replace the semaphores that used to be in service there with the B&O dwarfs. One other example is an experiment the B&O tried back in the early 60's, where they mounted dwarf signals on top of 10 foot mast for controlling trains by remote control - pictures here.
Here is a dwarf signal mounted to a steel plate which is
secured to the bolts at the base of the mast. It saves installing a
separate base for the dwarf. The B&O used this in most locations where
signals were placed at the end of a siding. Also notice the doll post,
telling the engineer the high signal controls the track to left, the doll post
is a place holder for the siding.
A three aspect dwarf in South Baltimore.
A three aspect dwarf at Bailey's Wye in Baltimore, with one
marker lamp.
A two aspect dwarf in Brunswick MD.
A full four aspect dwarf with two upper markers, also in
Brunswick MD.
A full dwarf with all six markers at the Brunswick MD Railroad
Museum.
Below are pictures of another example of using dwarf CPL's, this time for a non-standard use. Back in the early 60's, the B&O tried to implement radio control of the signals on a manual block section after a fatal accident occurred. They put dwarf CPL's up on the top of 10 or 12 foot tall poles, and re-lensed the signal so all of the aspects were yellow, like the Pennsy PL's are all single colored white. If you have the July 2004 issue of Trains, you can look for the story by Harold E. Meeker starting on page 50. Photos are used with the kind permission of Mr. Meeker, who is a most interesting fellow to talk to and has a rich railroad history and background, and if you are into coincidences, he lived about 5 miles away from me when we first moved into the Towson area of Baltimore back in 1966 while he was working for the B&O!! If you go looking for these signals, forget it, as they were removed shortly after the experiment ended. A bonus photo he sent me, and not in the article, is the one to the right of the equipment used in the test, an application using what we call today "COTS", or, Commercial Off The Shelf.
A pair of
back-to-back CPL's in Gaithersburg MD on the CSX mainline heading west to
Brunswick, adjacent to the fairgrounds. The "G" and
"D" signs are for eastbound traffic, such as the pictured freight. The "G"
sign is for "grade", as the freight is starting a downgrade from this
point. The signals are dark in the train picture, because the signals are
approach lit, and there is nothing in that block yet to light them up.... They
will light up once the train has passed the signals and entered that
block. The "D" stands for "delayed in block".
For an explanation of
the "D" signs and why they weren't used until 1996/7, see:
http://www.ntsb.gov/publictn/1997/RAR9702.pdf
Check out pages 38, 43, and 53.
Thanks to
Dave M. of the Yahoo Railway Signaling Group for the info on the "D" sign and
the link to this publication.
A single aspect, restrict only CPL adjacent to the Westport Light Rail station in south Baltimore.
The signal head & approach
sign.
The 3 signals below and Bailey's Wye are
shown on this B&O map of the central Baltimore MD
area.
South
Baltimore MD - Under I95
An almost full CPL
The right signal has all 6 markers... the only aspect it is missing is
restricting.
This GE just passed the restrict only signal above,
about a half mile ago.
Located in south Baltimore along the mainline
to DC at "Carrolls" - can be seen from NB I95 - Pix from
28AUG2005
South
Baltimore MD - Ridgely St
A 3
CPL signal bridge - located just south of Baileys Wye 082805
Signal head close-ups.
These heads are the same as the one I have in my
backyard. These things are built to last, as the background is 1/8"
thick. Notice that they are mounted on a slight angle, for the approach to
the bridge is on a curve.
Marker lamp close-ups.
Signal bridge details.
This signal is located just south of
Camden and Bailey's Wye - It's for northbound traffic.
For the time being, these CPL's, and
others on the south side of the Howard St tunnel have escaped the "Darth Vader"
signal upgrade project. It's not known how much longer these will be
around, so if you like 'em, go out and get your pix now!
It appears (so far) that most of the signals on the mainline between Baltimore and DC are intact, however, two new signal bridges went up in St. Denis/Relay last year, and the signals were cut over towards the end of 2007. CSX was very quick in taking down the two old B&O signals bridges on either side of HX tower.
South
Baltimore MD - Below Bush St 1
A CPL signal with 5 markers - for NB reverse traffic on the main line to DC in south Baltimore - 28AUG2005
South
Baltimore MD - Below Bush St 2
A couple of old CPL's placed on a
new cantilever bridge, just north of the signal above.
South
Baltimore MD - Washington Blvd
Two aspect CPL by
Washington Blvd and Monroe St, in south Baltimore
This signal is located just off the
Baltimore-Washington DC main line at Carrolls, it sits across from the old
Montgomery Wards warehouse at Monroe and Washington Blvd. There was once
two tracks thru here, and each track had a high signal for the main traffic
direction and a dwarf CPL for reverse traffic. When they took out the
second track, the CPL's went with it.
This signal is unique in Baltimore,
in that it has a pole mounted switch to cancel the crossing gates in the event
the train was going to sit at the crossing for any amount of time. There
are two other switches at this location, however, this is the only one mounted
on a signal pole. Pix from 11MAR2006.
Map of the
Bailey's Wye area
For a more detailed map of the Baileys Wye area, click HERE.
CPL on the
SW leg of Bailey's Wye in dntn Baltimore, for freights coming out of Riverside
Yard.
A couple of
shots of signals on the south side of the Harpers Ferry
tunnel.
CPL's a plenty at the west (south) end of Mt. Winans
yard in south Baltimore MD, with an approaching westbound CSX freight, taken
around 1995.
Most of these signals were
replaced by "Darth Vader" color light signals in 2007. CPL's around the
curve in Landsdowne were replaced a year or so earlier. The freight is
getting ready to cross Gable Ave, a fairly good photo spot off of Washington
Blvd, near Patapsco (I wouldn't venture into the yard, tho). This freight
might have come from Curtiss Bay if it took the crossover just off the right
side of the pix, if not, it took the long way around coming from Baltimore going
thru Mt. Clare yard A. For a B&O map of the area, click
HERE (same as the map above). The map is dated 1988, but does not
have the signal bridge by Ridgely St on it. Curious. There is a
little arrow on the map along Patapsco Ave that shows where the picture was
taken from. The map covers from Lansdowne Rd on the south side to Camden
Station (before it's current 2 track configuration).
This picture was taken from Gable Avenue, looking towards the place I took the above picture from.
At the bottom, you can see a CPL dwarf. At the top of the photo, and the two bright dots in the middle, are high CPL's. The two large white dots are streetlamps on the bridge that I took the other photo from, and finally, the cluster of three lights is a freight waiting to go into Curtis Bay, sitting under the bridge.
New 10-6-2006
Last
Modified: 24-Jun-2011
