THORN Tower Just Won't Die

Over the past few years I have been reporting on what turned into a rather protracted closure of Amtrak's THORN interlocking tower. What made THORN a bit harder to close was that it was opened in 1938 as part of a wide area CTC project to support the PRR's electrification to Harrisburg. While the typical solution is to remote control the CTC interlockings to a central dispatch office, Amtrak's desire to perform an a general Rule 562 re-signaling made it a better option to keep legacy operations with the tower and modernized ones in the dispatch office. Well it seems that despite the tower's closure on August 8th, 2026, one piece of its territory remains partly un-resignaled. 

GLEN interlocking, located at the eastern end of THORN's territory where the Dale Secondary, nee PRR Trenton Cutoff, joins the Main Line via a flying junction, appears to have not been fully re-signaled. While new eastbound signals have appeared on tracks 4 (PL mast) and 2 (PL dwarf), the westbound signals are still date from the PRR era with the implication that the 1938 relay hut is still in service.  On the other hand the Milepost 25.1 automatic signal has been removed indicating that Rule 562 is now in effect on that track to FRAZER interlocking where new signals were in place earlier in 2026. 

Since an interlocking with 1938 signals in one direction and 2026 signals in the other was not on my bingo card, I am going to offer two plausible scenarios for what is going on. The first is that plans for a new interlocking in the area has prompted Amtrak to hack up a hybrid GLEN until funding is available for what comes next. The second is that THORN's closure was based on an employee bid cycle, not re-signaling project completeness and Rule 562 between PAOLI and GLEN on track #4 and PAOLI and FRAZER on Track #1 will proceed as PennDoT funding allows. It could also be a combination of both these theories working in tandem. 

If any of you happen to be on a SEPTA R5 or Amtrak Keystone out past Malvern you can catch this mess of an interlocking for yourselves. Feel free to add your experiences in the comments. 

NS Files to Replace Cab Signals with Back Door CBTC

It was no secret that Union Pacific was planning to dismantle Norfolk Southern's significant cab signal territory that was inherited from Conrail after it was absorbed in 1999. While 91% of NS locomotives are cab signal equipped, few if any UP locomotives are after they dropped their own cab signal system around 2022 and a cab signal requirement would hinder creating a nation-wide pool of yellow locomotives. Well it seems that NS has decided to go ahead and file for discontinuance of the legacy Conrail cab signal system notwithstanding the results of the merger decision and what is perhaps even more interesting/alarming is the proposed replacement. 

Unlike CSX or Union Pacific, NS had made significant investments in cab signal territory that lacks fixed wayside signals (what NORAC refers to as Rule 562). While both CSX and UP disposed of their former cab signal territory by just turning it off in favor of existing waysides, UP-NS would have to replacement the wayside capability on hundreds of miles of high density main lines. On CSX's sole Rule 562 route, the former Conrail Boston Line, the solution has been to run trains under Rule 280a "Clear to Next Interlocking" and petition the state for money to restore the wayside block signals. Something similar was my expectation since the UP-NS was announced with UP installing its flavor of wayside block signals from Perryville, MD to Cleveland, OH.

Well, it seems that NS's plan is to implement a PTC based Rule 562 with the PTC system transmitting track authority based on track conditions. While this is pretty much a statement on how ETMS PTC works, the sea change is that everywhere else PTC is still subordinate to good old fashioned wayside signal indications. This removes a sizable chunk of safety and security burden from the system under the concept of "PTC can make you stop, but it can't make you go."  NS's request to the FRA would take ETMS as a safety overlay change it into a bonafide communications based train control system, possibly without any additional modifications. 

Like with CSX, the NS plan would remove the cab signal codes as a source of movement authority which requires the installation of ETMS wayside interfaces at every track circuit block point and hand operated switch. Unlike CSX, wayside signals would only be present at control points with Rule 280a "Clear to Next Interlocking" being the available for various PTC failures. 

The roots of this plan might lay with a trial "Rule 562" system Union Pacific installed on the Hiawatha Sub in Kansas. Since UP discontinued its Automatic Cab Signal system in 2022, the Hiawatha Sub did not gain wayside signals, just PTC antennas at the old Signal Indication Points. Since nothing bad seemed to happen on this low density main line on the prairie, UP might be looking to bring the concept to populated areas regardless of how secure ETMS really is. This might even be the camel's nose for what PTC proponents had envisioned, nationwide moving block signaling.

It's not entirely clear if the FRA will bite, but public comments would certainly help make them aware of the stakes.  Coded track circuits are a secure and reliable way of transmitting movement authority that cannot be easily hacked by AI agents or whatever. Wide area ETMS outages are not uncommon because the system is effectively running on servers in some back office. Of course when these occur its mostly the passenger operations that get canceled because that's where the liability is.  The real shame is that even if the locomotives are no longer responsible for picking up the codes, they will likely exist in the rails transmitting block state for decades to come.

Amtrak Zephyr Trip Report: The More Things Stay The Same

The last time I rode Amtrak's California Zephyr route was in 2017 just after there had been massive re-signaling over the Donner Pass, Utah and the Moffat Tunnel route compared to my previous trip in 2014.  Well 9 years later and surprisingly not much has changed, including the remaining instances of vintage signaling still on the route. 

Starting off with what has changed, UP completed re-signaling efforts over the Donner Pass including the few remaining signals around NORDEN. The SP vintage interlockings around Truckee have also been replaced, However most of the old SP era signal gantries remain standing and along with some of the now turned ABS signal masts on the west slope. Elsewhere on the Capitol Corridor some SP target signals may have been replaced by vertical color lights, but most are still intact. 

The "what stayed the same" list is much longer. First off is DAVIS interlocking which is still equipped with searchlights and a trackside pole line. Relay logic and a US&S unit lever local control power are likely still in the old interlocking tower. Unfortunately I didn't get any photos so here's stuff from 2017. 

In Nevada the SP re-signaled territory west of Winnemucca has been largely unchanged. 

Likewise the classic DRG&W signaling has been largely left in place between Helper and Grand Junction due to the lack of through traffic and the resulting PTC exemption. A few interlockings and ABS signal locations have been replaced and most still featured "turned" replacements, however little replacement progress has been made since 2017. 

BOND interlocking at the junction of the Moffat and  XXXX subs has retained its DRG&W signaling despite being in the PTC zone.  

Also on the approach to Denver Union Station UTAH JCT and FOX JCT are both intact with their original DRGW relay logic and searchlight signals.  

Like everything with signaling, the situation can change without warning so if you are road tripping through any of these areas plan on some side trips to visit these locations.  

Amtrak Electrification Primer

While this blog is dedicated to railroad signaling, I occasionally veer into the command and control of railroad traction power systems because not only does electric power have to be switched and dispatched, but historically it has used much of the same technology used for both railroad telecommunications and railroad signaling. 

Anyway I was recently informed that some documentation regarding Amtrak's present day electric power operation has made it onto the Internet Archive and its definitely worth a read because the documents cover all three of its electrified "zones" (PRR, Hellgate and "Boston") and contain all sorts of easy to read diagrams and photos. It also covers details about the "100hz" signaling power supply including its generation and control which absolutely puts this in the railroad signaling wheelhouse.

How To Be an Amtrak Power Director (2021)

Amtrak Electric Operating Rules and Instructions (2026)

I 'C' You - Caltrain Adopts SP Commuter Plates?

In the bi-polar mess that are Union Pacific Signal rules, an often overlooked feature are the < C > plates that upgrade Advance Approach and Diverging Advance Approach to Advance Approach [Commuter] and Diverging Advance Approach [Commuter]. These modifiers came about in association with the Caltrans funded Capitol Corridor service between Sacramento and San Jose and upgrade the speed restriction associated with an Advance Approach signal indication to 60mph from 40mph.While this falls way short of the 90-110mph operation and 60-80mph high speed turnouts the line should have, its at least a step to improve performance. 

SP vintage mast signals displaying Advance Approach with a < C > Modifier

Anyway, at some point between 2023 and 2024, [ C ] markers appeared on virtually all signals on the Caltrain main line. At first glance it appears that Caltrain was trying to take full advantage out of the performance of its new electric trains  boost the speed of following movements from 50 to 60mph where an unrestricted speed if normally 80mph. 

However a helpful reader left a comment that the new [ C ] plates are simply to mark the signals as displaying Caltrain's speed signaling aspects. In the route signaled area an [ R ] plate is used. I'm not exactly sure which problem Caltrain thinks they are solving, maybe the new MU service involved the hiring of many new operators, but [ C ] and [ R ] are not the best choices for a letter plate. [ C ] for the aforementioned < C > "commuter" tag and [ R ] for the common "permissive" modifier. 

Milepost 25.4 signal before modification. 

Of course there wouldn't be much stopping Caltrain from re-purposing the [ C ] plates to refer to 60mph Advance Approach via a rulebook change if the "speed signal rules" reminder tunes out to be unnecessary.  Just sayin. 

 

NS Re-Signaling Old NKP West of Cleveland

Although far less significant than recent re-signaling in core N&W territory, NS is currently going after routes that were last modernized in the 1980's when the N&W / Southern union was still being figured out. This generation of "NS" signaling was exemplified by Safetran SL-20 modules in a vertical configuration with a simple obround backing, along with mast poles with low cost strap on rungs. Recent photos from 2026 show that a resignaling project is underway on the former NKP main line east of Cleveland. 

Replacements will be of the standard NS type and will add more capabilities for Restricting indications in both a R/Y and R/R/Y form. It is unclear if tubular cantilevers and gantries of 1980's vintage will be retained or replaced. 

Protecting Sharp Curves Before PTC

Located at Milepost 90.3 on the former Rio Grande Moffat Tunnel route is a wonderfully analog system to help prevent inattentive train crews from derailing eastbound trains on an especially sharp 20mph curve. Despite the later deployment of ETMS PTC on the territory this holdover from the days of yore has remained in place and is observable by persons traveling on Amtrak California Zephyr Train 6. 

The Colorado Rockies have a geologic feature known as a mountain "park" which are wide flat valleys surrounded by generically mountainous terrain. The west slope of the DRGW Moffat Tunnel route alternates between impossibly tight canyons with a line speed of 25mph and these wide flat parks with long stretches of 60+ mph running. The mountain park near Kremmling, CO allows for 60+mph speeds between mileposts 82.2 and 86.2 on track that is close to tangent. At milepost 86.6 this abruptly ends in a wheel squealing 20mph curve as the line turns into Byres Canyon.  

To mitigate the risk of an inattentive crew hitting this curve at full speed a radio warning was installed at the milepost 90 automatic signal location. When an eastbound train is detected an audio message about the upcoming 20mph track is broadcast 4 times over the road channel. The distance between the warning and the curve is close to 3 miles and is more than sufficient for the engineer to control the train's speed.

The milepost 90 signal was replaced around 2015 when ETMS PTC was added to the line, however the radio message was left in place and today it serves as reminder of the sort of analog innovation that took place in the analog era like the timer based cab signal drops that were installed at similar high risk locations on the NEC in the 1980's.