A blog devoted to explaining the ins and outs of North American railroad signaling, past, present and future. This blog seeks to preserve through photo documentation the great diversity and technical ingenuity of 20th century signaling and interlocking hardware and technology. Related topics cover interlocking towers and railroad communications infrastructure.
Note, due to a web hosting failure some of the photos and links may be unavailable.
Not sure anybody noticed, but May 28th marks a decade since I started this blog as a place to archive long form signaling related content I had previously published on old school web forums with limited visibility. Due to an odd coincidence at the beginning, I have accidentally committed myself to and then maintained a 49 post per year schedule with signaling news, history and general overviews of some of the more obscure topics such as interlocking horns. Over the past decade there was been way more bad news than good and I can't say that things stand to improve in that regard, but it has still been my privilege to mark the passage of so many pieces of both railroad and technological history. If one was to ask what I was most proud of it would likely be the comprehensive surveys of PRR Main Line and Port Road signaling along with the documentation of the late great METRA interlocking tower interiors.
I'm sure a lot of people out there would use this sort of milestone to pivot to some completely new/different project like elevators or some sort of history of history of the Bell System, however as tempting as they are I still have a whole bunch of unfinished projects lined up for The Position Light and I hope you all will still around for them. These include, but are not limited to:
A B&O Main Line signaling survey between Washington DC and Pittsburgh, PA that features most of the now removed CPLs
Finishing up the remaining PRR Main Line interlocking towers that I have interior photos for including ZOO, PARK, CORK, STATE and AR.
Additional LIRR and METRA towers that I still have unreleased photos for.
These are just the marquee items as I will still keep pumping out the content, rain or shine, good news or bad, 49 posts per year. Thanks for reading. Check out my Youtube Channel where I do signaling related live-streams on a somewhat bi-weekly basis. Also remember to like, subscribe and don't forget to hit that bell notification. 😏
Today we are going to examine approach lit signals, what they are, their history, how they are classified and finally, who is using them. What they are is in the name. The signals only illuminate when the signaling system believes a train is approaching (or otherwise nearby). This is one of those things that people are likely more aware of than they think. The assumption is that a signal should always be lit as that's the way it works in traffic control. However anyone who lives around approach lit signals are quick to tell me that "those light up when a train is coming" since its hard not to eventually notice the pattern.
Approach lighting actually goes way back to the days of battery operated block signals where workers would have to physically haul out more electrons when any given signal's supply ran low. With LED technology decades away, the first solution was semaphore signals that didn't need electric illumination. Since this didn't work well at night, a second solution was to link an electric lamp to the track circuit relay in such a way that a shunt of the track circuit would close the lamp's circuit and illuminate the signals. Since railroad relay logic both then and now allow one input to control 8 or sometimes more other circuits in a single relay, this was a pretty straightforward arrangement.
Typical railroad battery case
Although pure battery based power supplies were eliminated over time, approach lighting remains fairly popular to this day. The first reason is that 440v pole line railroad power was both limited in transmission capacity and still not reliable and any fault could drop an entire line segment onto battery backup for hours or even days. The second reason is what most people would assume to be the first, saving on bulb replacement. while certainly a concern, low watt railroad lamps are pretty long lived as is and we can also observe the behavior of 20th century railroads to determine their motivations. Where railroad power was plentiful and reliable, think the PRR's electrified region with 6.9kv 100hz supplies or something like the N&W H-Line that was fed by a kv range 3 phase line supply, signals were lit full time where elsewhere on the same railroads approach lighting was employed.
There are several general classes of approach lighting that I have arranged into bins of my own design.
Type 1: Type 1 approach lighting is where a signal illuminates only when it's approach block is shunted. It's the simplest in concept and can be readily observed as when the tail end of a train passes the signal, the signal will deluminate.
Type 1a: This is an even more extreme version of Type 1 where on a multi
track line a shuntedn will only illuminate the signal that governs it.
Type 2: Here a signal location in CTC or other bi-directional territory
will illuminate in both directions if either approach block is shunted.
Therefore the signal will remain lit for a further period of time once
the end of the train passes.
Type 2a: Same multi-track effect as Type 1a, except also in both directions.
Type 3: Here a signal will illuminate if a shunt exists within the
entire line segment either in advance or in rear of the signal. This is
most applicable in single track CTC or Bi-directional ABS territory and
may or may not actually exist in real life.
Type 4: Another possibly theoretical example would be an approach
lighting scheme at interlockings where signals will illuminate if a
route is displayed, regardless of (or in addition to) track circuit
status.
At this point I have only ever fully confined the use of Types 1 and 2 approach lighting, however a number of anomalies have hinted at Type 3 or 4. There is of course another major exception to these rules in the form of non-circuited track like sidings, secondary tracks or yards. Signals governing these tracks must remain lit at all times as there is way to detect an approaching train.
Amtrak Hudson Line CP-156 showing the 24/7 lit siding dwarf and approach lit main track signal.
Use of approach lighting has varied widely in the time since power limitations became less of a driving force. Even where power is still provided by a pole line or solar panel, LED lighting would allow for 24/7 display of signals on a fairly small power budget. There is a small safety boost in that wayside signals can serve as an additional method to alert workers of an approaching train, however it is too unreliable to ever be codified into a rulebook. Even aggressive users of approach lighting will often make exceptions, especially in built up terminal areas once again pointing to power availability or signal access as a major factor.
At this point Union Pacific is the most aggressive user of approach lighting, employing Type 2a in all of its most recent signal projects. NS on the other hand is likely the Class 1 most in favor of 24/7 signals, often replacing Conrail era approach lit signals with full time. CSX uses a mix, but tends towards full time in contrast to the B&O, which was very much in favor of Type 1. Unfortunately I don't have enough experience with BNSF, CN or CP to comment on their specific tends however at a regional level the old Guilford favors approach lighting while the Reading and Northern splits the difference with full time at interlockings and approach lit at intermediates.
UP acting like its charged by the photon.
On the passenger side of things approach lighting is much less common as commuter railroads operate in dense metros that have has reliable electric power for well over a century. New Jersey Transit was probably the biggest user of approach lighting and with 1 mile blocks on many of its trunk lines it is possible to observe the next signal light up like a Christmas tree after passing the one before it. However new Rule 562 territory as well as the RiverLINE light rail have both tended towards full time. Amtrak used to use Approach lighting on its diesel lines like Michigan, Springfield and Atlantic, but has trended to towards full time, although the new CP-138 on the Hudson Line is approach lit. The other major commuter carriers such as Metro North, LIRR, SEPTA, MBTA, Metra and Caltrain all use primarily full time signals.
NJT signals at SAUK interlocking are Approach Lit, while those protecting the drawbridge at the joint Conrail interlocking CP-JERSEY are not.
From an fan perspective, approach lighting definitely has its pros and cons. Dark signals are certainly less interesting than lit and deprives one from being able to observe any routes lines up in advance. However the ability of approach lighting to act as a train proximity warning is highly useful, although could likely be replicated by a radio scanner. It also causes use of a so called "two minute drill" to get photos of displayed signal indications in the time between when a train enters a block and then passes the signal (or passes the signal and then exits the following block). Salience of the two minute drill actually confirmed the operation of mid-block Signal Indication Points on Conrail's cab signal territory as the approach lighting would only trigger once the approaching train passed the mid-block SIP instead of the previous wayside signal location, thus turning a 2 minute drill onto a 1 minute drill.
That's probably more than you needed to know about approach lighting. Unlike a lot of signaling trends this one is pretty neutral with neither definite trends in its use nor any major effect on the ecosystem either positive or negative.
I previously reported on the 2018 closure of LENOX tower a Big Four (NY Central) tower between Alton and St. Louis that had ended up under the purview of Union Pacific through the acquisition of the Chicago and Eastern Illinois route to Chicago. The tower was closed through a State funded rebuilding of the interlocking complex as part of the Chicago to St. Louis Lincoln Corridor project. Unfortunately, despite the tower being of brick construction and located in the middle of a major junction in need of maintenance, LENOX was demolished in May of 2021.
When I had last seen LENOX in the spring of 2019, the lights were still on and I had been told that the telephone etc still worked. The interior was thoroughly modernized with wall to wall carpet and HVAC. It looked like the Alton to St Louis rebuilding effort had finished with speeds raised on the old 40mph stretch between LENOX and WR.
Unfortunately
someone had other ideas because the tower found itself in the way of a
plan to remove LENOX interlocking's signature single slip switch and the resulting track realignment would require the demolition of LENOX tower. Although the the State of Illinois had some preservation riders in its
billion dollar corridor project, they only applied to the GRS Type 2
interlocking machine itself.
Despite the fact that two local rail museums turned down the request to save the interlocking machine, a local signal enthusiast got the call and managed to remove everything that was both transportable and worth saving. Anyone who might be riding the Texas Eagle between St. Louis and Chicago would be wise to get additional photos out the back. Moreover LENOX isn't in a built up areas so an in-person visit to the location would be unlikely to trigger much attention unless the rebuilding crews are on site.
Because of the unsustainable drive to create one seat rides, The State of NY has been eyeing sending New Haven Line Metro North trains over Amtrak's Hell Gate Line to Penn Station. If it were this simple I probably wouldn't be writing this post, but as part of it the state is looking to completely rebuild the line with 4 new stations and 6 new or rebuilt interlockings. This would likely not only mean the end of the existing amber position lights, but also any wayside automatic signals and possibly all position lights to better match the new color light signals in the East Side Access Zone.
The key features are the new track layouts and interlockings that will do much to restore the former 4-6 track passenger and freight corridor. Instead of just installing platforms along the existing two track line that sees at most 4 Amtrak trains per hour, New York would install a new pair of center placed tracks for stopping trains.
Hopefully a conservative backlash to funding Blue State megaprojects will keep the Hell Gate Line signaling intact for another couple of decades. Until then make sure you try and document it as best as possible, even though the only real way to get photos is to spring for Regional business class.
As with my previous post on the state of MG tower, I can confirm that AR tower is in a similar state of limbo, partly gutted of some components, but left standing and even more open to the elements. I found this video tour on YouTube showing the current state of AR Tower, but also the adjacent 100hz power house and compressor hut. Shockingly, the double Model 14 interlocking machine is still in place and roughly in the same condition I found it back in May of 2018.
If everything plays out right I should be able to revisit AR tower towards the end of May.
As I previously reported in 2019, Amtrak's FAIR interlocking in Trenton, NJ was having its pneumatic point machines replaced by electric M3's. I can confirm that this process has been completed and the air compressor infrastructure generally cut and disabled.
FAIR was one of the larger pneumatic plants remaining on the NEC, however a few others still remain such as HOLMES, PENN, RIVER, POINT, BAY, CHARLES, FULTON and LANDOVER. Of those PENN and BAY have been partly replaced and LANDOVER is slated for complete replacement by a new set of high speed crossovers. The New York Penn Station complex is also still pneumatic and is actually seeing refurbished A-5 point machines installed with the general rebuilt of the trackwork there.
In the fall of 2014 CSX completed multi-year re-signaling efforts in the heart of its former Baltimore and Ohio territory that included the Philly, Capitol, Metropolitan and Cumberland Subdivisions. B&O style Color Position Lights, some installed as late as the 1990's, were replaced by the typical hooded traffic lights. Beyond the odd siding exit, drawbridge, diamond crossing or distant on non-signaled track, the main line CPL era east of the Ohio River was over. There was however one notable exception on CSX in the form of GREENBELT interlocking in Greenbelt, Maryland. Located just inside the Beltway adjacent to the DC Metrorail-MARC transfer station of the same name, GREENBELT was distinctive in being an interlocking that only really served the MARC commuter train service. These CPL signals would stand for an additional 6 years until their replacement in late 2020. In May of 2020 I went out to GREENBELT for a documentation run so I could present to you photos of The Last CPLs.
GREENBELT interlocking was installed in 1992 as part of a general
re-signaling of the Capitol Sub to better support the MARC Camden Line.
This saw the elimination of any residual Rule 251 ABS territory, a new
Camden terminal complex in Baltimore and the closure of any remaining
manned towers such as JD TOWER in Hyattsville. Both the Capitol Sub project
and a similar one on the Metropolitan Sub turned out to be some of the
last where B&O CPLs were installed new. Like several of the new
Capitol Sub interlockings, GREENBELT was commissioned solely for the benefit of MARC
commuter trains and consisted of two side pocket tracks that would provide
an ADA compliant high level platform connection to DC Metro's new
Green Line terminus (The The Americans with Disabilities Act having
recently come into force). Pocket tracks were necessary as high level
platforms conflict with the clearance envelope of main line North
American freight trains. The interlocking consists of two switch pairs,
#1 and #2 and 4 signal pairs, 1E/1W. 2E/2W, 3E/3W and 4E/4W.
The signals were in turn broken down into 4 high mast CPLs for the main tracks and 4
dwarf CPLs for the pocket exits. The dwarf signals were placed
following the old "right hand" style, while the high masts were not.
In addition to the 12 o'clock orbital for normal routes, eastbound main
track signals sported 6 o'clock orbitals for Medium speed diverging
movements into the pocket tracks as well as 10 o'clock orbitals for
Approach Medium indications for crossover routes at AMMENDALE
interlocking, one full signal block beyond GREENBELT.
Eastbound pocket track signals featured a 6 o'clock orbital for
diverging routes back onto the main line as well as an 8 o'clock orbital
for Medium Approach Medium indications when trains needed to
immediately diverge again at AMMENDALE.
The westbound signals have a slightly more complicated history. As originally configured westbound main track signals featured both 10 o'clock and 2 o'clock orbitals for Approach Medium and Approach Slow indications respectively. This is because GREENBELT was also one signal block away from the former JD TOWER complex in Hyattsville. Trains approaching from the east would get an Approach Medium for track 1 to 2 crossovers or routes onto the Alexandria Extension at RIVERDALE PARK interlocking. However if a Stop signal was displayed at JD TOWER interlocking, a Slow Approach indication would be displayed (at least for diverging routes) at RIVERDALE PARK due to the short block distance between RIVERDALE PARK and JD TOWER. This then necessitated an Approach Slow capability at GREENBELT.
The westbound dwarf signals operated in a similar manner, just with a
full row of lower orbitals including an 8 o'clock orbital for Medium
Approach Medium and the somewhat rarer 4 o'clock orbital for Medium
Approach Slow.
