Caught on Camera: Track Circuits and Electrification Current

In a previous post covering the phenomena of a "bobbing" track signal that cycles intermittently between one or more states. I mostly covered the spectacle of a particularly egregious example on SEPTA's former Reading Main Line. Here I will cover two additional examples that are a bit more tame, but sheds some light into some operational side effects that come with railroad electrification. 

PATCO FERRY interlocking with an eastbound train on the troublesone WF2 track circuit.

The first example was caught on the PATCO Speedline and involves the cab signal bobbing between 30mph (Approach) to 65 mph (Clear) immediately after a westbound train crossed over to the eastbound track just past the Ferry Avenue interlocking. Was this cased by standing water or a lose wire? Apparently this bobbing signal is a known issue that occurs when the operator or ATO system selects the P4 power setting after exiting the turnout.  The current draw causes the WF2 track circuit relay at West Ferry interlocking to drop.  With the WF2 and NJ67 track circuits both occupied, the signaling system thinks that the train is still on the 30mph switch at West Ferry and drops the cab signal from Clear to Approach.  The train cuts power, the WF2 relay picks up, the signaling system "sees" the train off the 30mph switch and upgrades the cab signal to Clear again.  The process continues until the train passes the next code change point.

As I explained in my post regarding impedance bonds, the rails serve double duty as both a path for traction return current and the track circuit. Because of this a mis-calibrated signaling component can be affected by the acceleration state of nearby trains.    A "safe" failure of this type is less likely to be tested for upon installation or fixed quickly once identifies.  A good example of this is the southern segment of Amtrak's Northeast Corridor that still utilizes relay--based signaling hardware from the early 1980's.

Like with the PATCO example I have been told that the interaction between the signaling system and electrification can be to blame, especially from trains traveling on adjacent tracks. The first example was located at the northbound Milepost 69 intermediate signal near Aberdeen on the less frequently utilized center track #2. The signal can be seen slowly cycling between Clear and Approach, potentially due to an electric train movement on one of the outer "through "tracks". 

Here we see a slightly more extreme example as the southbound Milepost 103 intermediate signal on track #2 at Halethorpe rapidly flickers between Approach and Clear. It might look like Advance Approach is trying to display, but the signal blocks ahead are of usual length and the flicker interval is not uniform. This was noticed after the passage of a southbound Amtrak electric train on track #1. This instance of signal bobbing would also be likely to avoid rapid resolution as track #2 is less frequently used than tracks 1 and 3 and for at least half the day traffic is set in the opposite direction. 

Milepost 103 signal location with track #2 set northbound

Years ago when I had access to Amtrak NEC reports, there would be bobbing signal issues that would persist indefinitely. When the cause is an intermediate side effect of the electric traction system, these problems can become very difficult to troubleshoot as they might require a train running at some specific power load/speed to trigger the problem. A big reason central European countries are so enamoured with axle counters is that many electrified before installing automatic signaling. Counters solve both the problems associated with impedance bonds, but also problems like bobbing signals. 

Caught on Camera: New CSX Signal Rules in Action

A few months ago I posted about CSX's two new "Canadian" style signal rules, 281E Limited Approach Medium and 281F Limited Approach Limited, to augment its existing Rule 283A Medium Approach Medium and 283B Medium Approach Slow. Although established in 2024, I had not been expecting to catch one in the wild for some time as railroads tend to bend over backwards to avoid signal modifications if they can be avoided. Sightings of the new signal indications had mostly been in former Seaboard System territory in Georgia and Florida. Therefore you can imagine my surprise when, after stepping off Amtrak Empire Service Train 281, I saw a Rule 281D Limited Approach upgrade to Rule 281F, Limited Approach Limited at Chicago Line interlocking CP-292.

Now Rule 281D Limited Approach has been present on the Seaboard main lines for several decades, and although it is an odd duck, by seeming to authorize Limited speed up to a stop signal instead of Medium, this could have been present as part of the general Chicago Line re-signaling of the 2010's. The Rule 281F indication has to have been added since September 2024  so that is evidence of more system-wide changes on the part of CSX. 

As to why CSX is retrofitting existing interlockings as opposed to using 281E/F only in new projects my guess would be this is a downstream cost of PTC speed enforcement. Not so much in the sense that crews would "cheat" when 283A Medium Approach Medium was displayed for Limited Speed turnouts (although they probably did), but PTC's conservative braking curves could be raising the cost of signal indications that leave speed on the table. 

Amtrak Harrisburg Line Re-Signaling Hits FRAZER

I have previously discussed the drown out closure of Amtrak's THORN tower in Thorndale, PA. Recently the re-signaling efforts have hit FRAZER interlocking where new colorized position light masts have replaced the old amber style PLs. This is just another symptom of the eastern end of Thorn's territory being converted from its 1937 ABS 251 CTC to contemporary Rule 261 CTC. 

FRAZER is an interesting part of THORN's zone of responsibility. As covered in Part 2 of my old PRR Main Line signal survey, FRAZER was placed in service around 1994 when the old Paoli MU shoppe complex was closed due to massive PCB contamination stretching back to 1915. As a replacement a new yard and inspection shoppe was opened near Frazer, PA, extending basic SEPTA R5 service an additional stop to Malvern, PA. The only problem was that there was no interlocking infrastructure at the Frazer location to to support what is SEPTA's busiest commuter rail line. The solution was a new interlocking, FRAZER, that consisted of a yard lead, a turnback track and a center pocket track where eastbound R5 trains could wait for any conflicting movements to clear up.

There was some initial debate about whom would control the interlocking as in 1994 the entire Amtrak Harrisburg Line was still paper dispatched and FRAZER was located directly between the territories of THORN and PAOLI towers. A 1994 fire at BRYN MAWR tower forced the issue when PAOLI  took remote control of that interlocking leaving only THORN with the necessary spoons for more territory. However the increased workload did bump the operator's position at THORN to that of a higher paid Train Director. 

Because FRAZER was located in single direction Rule 251 territory about 4 miles from an existing interlocked crossover, it was not deemed necessary to give FRAZER universal crossovers of its own, so only a training point path was provided mainly for R5 trains heading east. Because this part of the Main Line was built with 4 tracks, there was ample room for a centrally placed pocket track. 

FRAZER is likely the last new Amtrak interlocking constructed with amber PRR position light signals. By 1994 the conversion of the NEC to colorized PRR position lights (a downstream outcome of the Chase, MD wreck) was well under way, but with no plans to convert the old PRR Main Line (Amtrak Harrisburg Line) FRAZER was designed with amber lamps for the sake of commonality. This view was incredibly short lived as PAXON and WOODBINE interlockings built to support the new Overbrook Maintenance Facility just a year or two later would have the position color lights.

It is unclear if FRAZER's conversion is part of a full re-signaling or just a modification to support both the colorized signals, bi-directional operation and Rule 562 cab signals without fixed wayside signals. Dwarf and pedestal signals unaffected by\the changes do not appear to be facing replacement along with the primary relay hut. New Rule 562 signal indication points between FRAZER and THORN are in place along with new signal equipment at GLEN and the planned decommissioning of DOWNS. If I am not mistaken, this will also be the first time SEPTA crews have to deal with Rule 280a "Clear to Next Interlocking" signals on their regular territory as their own Rule 562 territory lacks this feature, instead handling cab signal failures with dispatcher issued Form D's.

Former Dallas Terminal Railroad Re-signaling

 The Dallas Terminal Railroad can be considered to be in the midst of a slow-motion re-signaling, partly set off by Amtrak move from Union Pacific to TRE routing between Dallas and Fort Worth. This matters because the stretch of of 5 back-to-back interlockings, while "modern" in appearance, actually represents a vestige of late stage relay interlocking installed in the 80's or 90's with quirky signals of a non-Safetran nature.

The stretch in question used to be covered by the Dallas Terminal Railroad's Towers 106 and 107 that managed the west and east ends of Dallas Union Station. This has since become part of the Union Pacific Dallas Sub and from east to west consists of REUNION, DALLAS, JFK JCT, TRE JCT and INDUSTRIAL X-OVER interlockings. An additional interlocking, BN CONNECTION, makes up the third corner of the wye with TRE JCT and JFK JCT.

Around 2015 Amtrak shifted from the UP Dallas Sub to the ex-Rock Island Trinity Rail Express commuter route west of Union Station. Around 2023 the switch that connected the Amtrak platform at Union Station to the Dallas Sub was removed along with the west leg of the wye, turning both TRE JCT, BN CONNECTION and the TRE portion of JFK JCT into vestigial interlockings with signals guarding empty track. REUNION also saw the removal of the crossover to the east end of the Dallas MoW/passenger car storage track. 

In 2026 the other shoe dropped with the vestigial JFK JCT signals being removed and new signals going up at DALLAS. I don't know the exact plans, but there are two clear options. The first is that DALLAS loses its crossover and becomes an interlocked connection to the MoW stub with other interlockings staying unchanged. The second, and what I consider to be the more likely scenario, is that JFK JCT will be merged into DALLAS with INDUSTRIAL XOVER and the vestigial TRE JCT being eliminated along with BN CONNECTION. Currently trains on track #1 encounter 4 signals within 3000 feet, not a situation that is likely to play nice with PTC. Moreover, INDUSTRIAL XOVER duplicates the facing point crossover available at DALLAS. While its possible INDUSTRIAL XOVER might be kept something tells me that it is surplus to requirements.

So why does this all matter? Like I said the current setup uses late stage all or partial relay logic and non-Safetran signals consisting of L&W modular and GRS monobloc equipment. Second the close signal spacing introduced some very interesting signal progressions. In fact because of the sharp turn of the Dallas Sub at JFK JCT, the default progression for track #1 westbound is an Approach Restricting at DALLAS to a Diverging Clear (straight clear is onto the TRE) at JFK JCT. I suspect the new interlocking will display a Clear to UP train movements despite the curve. All together, what is an accessible place to observe interesting signal indications on interesting signals is about to get much less interesting, even if the exact amount of uninterestingness remains to be seen. 

 

Caught on Camera: PORTAL's new "Gantrylever" Under Test

Following up on the previous post regarding the new PORTAL bridge cutover, Amtrak I happened to catch a cab speed indication on the (New) PORTAL interlocking's westbound cantilever mast's 3W signal. With the new track #3 still very much under construction, crews were getting a jump on commissioning* the new interlockings associated with the project. Although this is a static image, the 3W was displaying a flashing green cab speed indication, which would be in line with the high density cab signaling in place between HUDSON and A interlocking at Penn Station. 

That alone is interesting, but if you review the track and signal diagram from Bulletin Order establishing OLD PORTAL and OLD SWIFT interlockings you might notice that future PORTAL is intended to be laid out similarly to OLD PORTAL with center Track A merging into tracks 2 and 3. Instead in the photo we see a two track cantilever mast, or do we?

Amtrak is splitting the commissioning of the new Portal fixed bridge into two month-long work sessions spaced 6 months apart. The primary reason for this is that activating the new eastbound track #2 will require the prior removal of overhead catenary supports required for both existing tracks. A secondary reason is that the new track 2 will require partly burying the old track 3 and removing the westbound cantilever as you can see below. 

If you look closely the end of the cantilever arm has some extra bits and the diagonal supports at the corner seem a bit flimsy. This is because that new signal structure is not a cantilever, but half of a three track signal gantry that will be completed once its southern foundation has something to sit on. I'd call this a "gantrylever", but that term is somewhat taken by gantry+cantilever combinations as seen at UNION and DUNTON. 

 In other news related to PORTAL's signaling  the lower heads on the westbound signals are conforming to the new pattern established at LEGGETT interlocking on the Hellgate Line, replacing the central lunar white Stop and Proceed dot with a a lunar white Restricting \. However the eastbound signal masts retain the Stop and Proceed dot. This might be a quirk needing the shorter signal blocks around Secaucas transfer than the SWIFT connection. 

Anyway. just though it was cool to catch the new temporary cantilever signal 3E under test, several weeks before the first revenue train would actually use the new bridge.

*Note: Amtrak would ultimately open track 3 for service two days ahead of schedule due to a problem that fouled track #2 during the morning rush. 

 

Amtrak PORTAL Bridge Re-Labeling

The requirements of safety and signaling made railroads some of the first organizations to manage systems of unique identifiers and all their associated corner cases. Today we will explore how Amtrak is handling some of these corner cases as they replace the historic PORTAL swing bridge on the Pennsylvania Tunnel extension in the New Jersey Meadowlands.   

1910 vintage PORTAL swing bridge.

Let's first discuss names. Originally "W" cabin, PORTAL's current name emerged around the 1930's when increased use of voice-based telecommunications prompted the PRR to switch many of its interlocking identifiers from telegraph letter codes to names evocative of their local surroundings. At the time the swing bridge and its crossovers were the last interlocking station before the western portal of the North River Tunnels, thus PORTAL. In the mid-1990's Amtrak and New Jersey Transit implemented a connection between the DL&W main line and the Penn Station tunnel route immediately west of the PORTAL bridge. Branded Mid-Town Direct, this service would drastically decrease trip times compared to the 2-sear ride via Hoboken and someone came up with the name SWIFT for the new junction. 

"New" Eastbound PORTAL signal gantry over PRR era gantry.

 

Westbound gantry at SWIFT with route indicators.

The other important labeling system is for the universe of railroad tracks. It might seem straightforward to just start at 1 (or A) and advance upward, but on which side of the right of way does one start counting? What if you need to add a track on the "below" 1? I'll make a post about track numbering at some point, but in this case the PRR was forward looking and went with track #2 (eastbound) and #3 (westbound) since in 1910 it was foreseeable that traffic growth would require tracks #1 and #4 at some point in the future. When the Secaucus Transfer opened, the layout placed slower station tracks between main tracks #2 and #3. These were given letter designations with tracks A and B. PORTAL interlocking was even expanded to include switches into the western end of track A.  

1990's PORTAL extension to support new Track A with 80mph turnouts.

Fast forward to now and Amtrak is building a brand new PORTAL replacement bridge that will also replace most or all of the current PORTAL and SWIFT interlockings. However for the better part of a year both old and new bridges and tracks will be in service and keeping the names the same might result in safety critical confusion. As a result Amtrak proactively renamed the old tracks and interlockings in December, 2025 with PORTAL becoming OLD PORTAL, SWIFT becoming and OLD SWIFT, track #2 becoming track #22 and track #3 becoming #33.

It gets better because Amtrak employs a track number based labeling system for signals and interlocking appliances. This made signals like 2E and 3E into 22E and 33E. Likewise switches like #23 and #32 became #2233 and #3322. Note that lettered tracks are just assigned a number for the purposes of switch and signal labeling with 7 standing in for A, but because track A doesn't cross the bridge there was no need for it to participate in the renaming. 

The now renamed 2233 crossover and 227 turnout at SWIFT.

Like automatic signal number plates and interlocking station signs, track numbering is a fascinating topic that I will dive into at some point, but for now I'll leave things in the context of a topical news item. 

PHOTOS: LEAMAN - The Place To Be

The Pennsylvania Railroad Main Line, today operated by Amtrak as their Harrisburg Line, is known for its many interlocking towers that survived well into the 21st Century and I have covered several of them on this blog. However there is one "place" that isn't quite a tower, although it has many of the trappings of one. While the PRR seemed to have an aversion to CTC, it still had a lot more signaling infrastructure than peer railroads with a particular focus on Manual Block System and its related component, the block station. What's a block station? Well its a location on the line that can host a block operator who in turn can perform those duties necessary for some (manual) block operation like transmitting train orders, displaying signals and throwing hand operated switches. Even on signaled PRR main lines one could find non-interlocked block stations open either 24/7 or part time.

Located at milepost 56.7 between PARK and CORK interlockings on the Main Line is the town of of Leaman Place. You might recognize the name for being the interchange point for the Strasburg Railroad. This segment of the Main Line was electrified in 1939 and at the time  featured 4 main tracks. Despite the 24 mile gap between the two interlocking stations, no intermediate crossovers were provided as most disruptions could be dealt with by relying on the "spare" main track (with the parallel Columbia Branch directly providing an additional two tracks of relief capacity for freight). However in 1948 tracks 2 and 3 were removed due to declining traffic and evidently this length of single track operation during maintenance or equipment failure had become an issue because in 1961 the PRR constructed the new LEAMAN block station at milepost 57.0 with a pair of main track crossovers protected by semi-automatic signals. Unlike similar hand throw block stations LEAMAN had no normal hours of operation and was only open as needed for single track operation.

LEAMAN consisted of a pair of center locked hand operated crossovers and a pair of position light signals oriented in the normal direction of travel. As this was not an interlocking, no reverse direction signals were not installed. A rather robust operator's shelter was provided and outfitted with  station signs, climate control and telecommunications. 

This sort of hand operated crossover layout was not uncommon on other double track ABS main lines with the requisite "shelter" typically taking the form of a wayside telephone booth that would allow crews to call the dispatcher to pick up their movement authority to run through the single track area or to report clear of it. However LEAMAN was unique in that its signals and electric switch locks were tied to a small control panel inside the operator's shelter and not accessible to road crews. 

Caught on Camera - NORAC's Missing Signal Aspect

If you are looking at older versions of the NORAC signal aspect chart you might notice something a bit odd. Most of the common signals indication have a dwarf option for situations with restricted clearance like tunnels or terminal areas. Because of the understandable choice to limit dwarf signals to 1 or 2 elements, some uncommon aspects like R/Y/G Medium Approach Medium are omitted, however until 2018 NORAC also omitted a far more popular signal, Rule 285 "Approach". For those of you who have been living in a cave, Approach, also known as "Caution" in the UK, is "the yellow light" in railroad signaling. A signal so basic that it appears in elementary school books on how trains work. How Rule 285 was neglected in dwarf form is an interesting story of path dependence. 

The story begins with the lamp color yellow performing double duty as for the Restricting indication. When shown alone on a dwarf signal, yellow Restricting, not Approach, so Approach has to be something else. Well, we have two lamps so why not make Approach Y/R? Well dwarf signals are most often used in terminals, terminals are slow so dwarfs really need a Slow Approach indication.  Single lamp *Y* flashing yellow exists and is the preferred option, but back in the day flashing relays were expensive and unreliable so we should probably have a fixed version of Slow Approach. This is where the fateful choice was made. R/Y Slow Approach could have worked. If the Red lamps burns out the signal becomes a Restricting, but the rules boffins likely didn't want R/Y Restricting on a high signal to be confused with R/Y Slow Approach on a dwarf signal because that mistake would likely result in an accident. Therefore dwarf R/Y was given to Restricting, Y/R was given to Slow Approach and Rule 285 Approach was out of luck.

Slow Approach on Track 1 east at CP-97 instead of Approach.

For the sake of correctness NORAC did offer Rule 285 Approach in the form of a PRR pedestal or a B&O dwarf CPL, but these were never options in color light territory or after position light signals began to be phased out. So what was a railroad to do when it needed Rule 285 in a restricted clearance situation? First option was to use Slow Approach, one loses 15mph within interlocking limits, but outside of interlocking limits the rule becomes "regular" approach with a Medium speed limit. The second option was to use Y/*R* Medium Approach, this bumps the speed passing the signal up from Slow to Medium, but ultimately suffers from the same drawback as Slow Approach in that trains can't come at either of these substitutes on a Clear, trains have to hit an Approach Medium or an Approach Slow first. From my field observations Medium Approach was the preferred alternative and could be displayed on either a 2 or 3 lamp modular stack by lighting the yellow lamp and flashing the red below it.

To be fair, the Seaboard system used by CSX also exhibits this problem despite using only using lunar for Restricting with dwarf Y/R for Slow Approach and R/Y for Medium Approach. By forgoing a flashing medium approach CSX lost its latitude for an "easy" dwarf approach aspect. However it was ultimately NORAC that cracked first and in 2018 they adopted *Y*/R as the dwarf option for "straight" Rule 285 Approach. While this now leaves Rule 282a Advance Approach out in the cold, Approach Medium is pretty much a lossless substitute. Of course these sorts of changes can take some time to filter down and it was only recently where I managed to catch one in the wild at SEPTA's WAYNE JCT where a dwarf has replaced a high signal at the end of a platform.

With this change the ball lands back in CSX's court. Will they make some basic changes to its system like adopting *Y* Advance Approach in addition to *Y*/R dwarf Approach?  Or will they keep looking for more "Canadian Combinations".

CSX Signal Rules Go Canadian

In September of 2024 CSX added two new signal rules to its rulebooks, Limited Approach Limited and Limited Approach Medium, and examples of both are just starting to appear in the field. In fact I believe this is the first use of a non-cab signal related multiple lamp flashing signal in the United States. If these rules and multi-flash aspects sound both strange and familiar at the same time its because these sort of "combination" signal rules are a standard thing north of the border in Canada. 

Since the steam era our friends up north have taken the concept of speed signaling to a bit of an extreme with every possible combination of one speed going to another speed given an explicit signal rule. You want to go Slow Speed to Limited and Limited to Slow, Canada has you covered. 

Everywhere else in North America has realized that this extreme amount of signal rules is dumb and will lead to confusion and higher training costs. While some combination indications like Medium Approach Medium or Medium Approach Slow occur frequently enough to be worth including, the remainder are unlikely to see much use and are better off being substituted for (for example downgrading Limited speed combinations to Medium) or covered by special rulebook instructions like NORAC famously allowing trains to diverge over an Approach X type signal indication if the previous signal was not Clear. Anyway it looks like CSX has thrown its lot in with the Canadians and started to care that trains keep that extra bit of Limited Speed when diverging back to back. 

Limited Approach Medium was spotted at on A-Line at SOUTH MICRO where southbound Amtrak Carolinian Train 79 will make an early divergence to its eventual turn off at SELMA with the NORTH SELMA crossovers in between. While the NORTH SELMA crossovers are Medium Speed, T79 would be taking a straight route there so many they just wanted to get it slowed down early for the tight turn onto the H-Line an additional mile beyond. Youtuber Danny Harmon managed to catch a Limited Approach Limited at 10TH ST interlocking on the Vitis Sub. He was also puzzled as to the purpose as the next two signals in the northbound direction were intermediates at standard 2 mile intervals. 

Anyway if you would like my opinion of these new signal rules, necessity aside CSX did a good job picking from those signal aspects that were available to them. Despite CSX's major screw up picking R/Y/G as Medium Approach Slow, which forced Medium Approach Medium to use R/Y/*G*, that mainly presents a problem for a potential Medium Approach Limited. Using R/*Y* for these Limited Approach X signals jives with CSX choice of R/*Y* for Limited Approach. Thus we have Rule 1281-D R/*Y* Limited Approach, 1281-E(?) R/*Y*/G Limited Approach Medium and Rule 1281-F(?) R/*Y*/*G* Limited Approach Limited. (Note I could not determine the actual CSX signal rule numbers at this time so those are my best guesses).

Hoboken Terminal's Suspended Signals

Stations with large terminal fans often exhibit a problem at one or both of edge tracks. Because rail vehicles can't generally make hard right turns, one needs a longer series of switches to reach the highest and/or lowest track. Unfortunately terminals often abut a fixed location like a river or street or public square and to avoid having those extreme tracks things can get a little squished. In the early 1980s, New Jersey Transit engaged in a near total reconstruction of the former Delaware, Lackawanna and Western electrified suburban network. Not only was the 3kv DC traction power system under powered and on its last legs, but the signaling system was firmly rooted in the 1920's. In the re-signaling project that followed, NJT built the last great North American interlocking tower, TERMINAL TOWER and replaced most vestiges of the former DL&W plant.

New (frame left) and old HOBOKEN TERMINAL TOWERs shortly before cutover.

In the late DL&W era Hoboken Terminal signals consisted largely of two head, small target searchlight signals displaying the DL&W's unique mix of color light signal indications. Long platforms in the center of the terminal had these mounted on signal gantries in the normal way, while tracks towards the edge of the low 1908 train shed saw signals mounted below the gantries under the shed itself. Moreover, while center tracks could get a "straight" clear out of town, tracks towards the edges had to make do with a Restricting indication as the DL&W lacked Slow Clear and Slow Approach options, even on dwarfs. 

When NJT rebuilt the signaling there appears to be a time when the new signals were wired into the old HOBOKEN TERMINAL tower's old US&S 1908 Electro-Pneumatic interlocking machine. To make the cutover process easier, signal locations were largely kept the same, but NJT had no desire to keep the old handicap of trains of edge tracks departing under a Restricting signal indication. This meant that the replacement "high" signals had to display R/R/G Slow Clear as opposed to the G and G/G on a dwarf. In most locations this wasn't a big deal as the signal gantries could easily support three tri-light heads, however on tracks 2, 3, 12 and 13, the need to suspend signals under the trainshed due to the closeness of the first switches presented a bit of a problem.

TERMINAL TOWER 36W2 and 36W1 suspended signals governing tracks 3 and 2 respectively.

TERMINAL TOWER 88W and 92W suspended signals governing tracks 13 and 12 respectively.

The solution was somewhat akin to a Penn Station signal, just with three "heads" instead of two. To display R/R/G, R/R/*Y* and R/R/Y, two fixed Safetran modular dwarf cubes were mounted close above an additional three-unit cluster of modular dwarf cubes. These were then mounted close under the roof at the westernmost end of the trainshed.

36W2 signal governing track #3.

 

Although a bit inelegant compared to a dwarf or today's compact LED searchlights, they are a unique solution in today's largely homogeneous signaling environment and are likely to persist for many years to come. 

Dispatcher Signal Stacking

The story of railway signaling, like many others, has been one of technology increasing human productivity. Power operation allowed "levers" to be thrown faster, N-X machines allowed routes to be set with fewer button presses and remote operation combined with CTC allowed one person to control many miles of track. However remote control and ease of operation were not the only types of automation added to towers and dispatch offices. Fleeting allowed infrequently manipulated interlockings to do the same thing over and over and in cases where routing decisions needed to be made, automatic route setting combined with train labeling could keep track of train movements and automatically request routes as they approached junction points.

Recently another method of automation has crept into dispatch software, route stacking. While similar to automatic route setting, it is different in a significant way. Consider the following pair of photos showing an Amtrak Springfield shuttle train departing SPRING interlocking at Springfield Union Station.  

 

Within seconds of clearing the interlocking the 2N dwarf signal (upper right of the photo) changes from Stop to Restricting for an opposing movement. In the past this would signify a very attentive dispatcher, hovering over their CTC panel or video display, ready to line the new route as soon as possible. If this was an auto-routing system we would have had to wait for the opposing movement  to enter the track segment to trigger the route request.  With stacking the dispatcher simply uses their computerized dispatching interface to queue up a sequence of routes which will be executed as soon as the last established route is taken. Then they can do and pay attention to something else.  

This works well at places like Springfield where reverse movements are common. For a northbound train the dispatcher could set up a route from the 2S at SWEENEY, 12 switch reverse. Then immediately have a second route set for the 1N 13 switch reverse to the CT River Main Line.  It's not super complicated, but it is something that, due to the time penalties associated with bad routes, took a little while to catch on.

Amtrak's New Position Light Configuration

Following from Pennsylvania railroad practices, Amtrak used the following two configurations for all of its "complete" position color light mast signals at interlockings. They either have a lunar white Restricting \, or they don't. In both cases the single central lunar white Stop and Proceed marker has been retained.  

While most other North American railroads have shifted to using Restricted Proceed in place of Stop and Proceed, Amtrak, and the NORAC rulebook for whom Amtrak is the biggest member, have both retained the Stop and Proceed practice.  

So consider my surprise when saw the recently installed colorized position light signals at Amtrak's new LEGGETT interlocking on the Hellgate Line. The restricting \ is present, but, please correct me if I am wrong, I believe this is the first time I have seen Amtrak PL interlocking signals without a Stop and Proceed marker. 
 

Part of  the Penn Station Access Project, these colorized position lights are the first of many that will wipe out the last stretch of amber position lights on the NEC (PHIL is a point, not a stretch) and they appear to indicate a shift at Amtrak towards that all important stop before entering an occupied block.

In case your wondering the typical Amtrak signal progression is to display a Stop and Proceed if there is an obstruction within the interlocking limits and a Restricting (if available) if the interlocking is clear, but the block beyond is not. The stop certainly seems like a worthwhile safety precaution, but the distinction between it and Restricted proceed is minimal, mostly just the salience of entering a stretch of track with an obstruction or broken rail. 
 

As you can see the new signals on the replacement Portal Bridge have retained the Stop and Proceed marker, but that project was designed and specified some years before Penn Station Access. So it remains to be seen if this is the shape of things to come, or a one off trial.