Amtrak THORN Tower to Close Aug 8, 2026

For over a year I have been tracking the slow motion closure of Amtrak's THORN interlocking tower. located on the old PRR Main Line in Thorndale, PA Opened in 1938 as part of the PRR's electrification project to Harrisburg, THORN was equipped with a state of the art CTC unit lever console controlling  4 remote interlockings in addition to the local 6(!) track full crossover. THORN's extended territory, including FRAZER interlocking which was commissioned in 1994, is what has allowed for the prolonged multi-year closure, which will take place just shy of the tower's 90th year in continuous operation.

Since the first part of THORN's territory, CALN interlocking, was chipped away back in 2020, the local 6-track crossover was rationalized and then turned over to CTEC control while the THORN operator continued to handle SEPTA movements in and out of Frazer yard as well as the daily NS freight entering the line at GLEN. More recently DOWNS interlocking was prepared for complete removal, its signals left standing as the change point between CTEC and THORN's control.  In the final act, kicking off in early 2026, GLEN and FRAZER interlockings were reconstructed with the goal of a Rule 562 cutover once all of the work had been completed. 

THORN interlocking as rationalized in 2023

The closure will bring full bi-directional operation between THORN and PAOLI, with the segment between FRAZER and PAOLI remaining outside the Rule 562 zone for now. The much diminished PAOLI tower is likely next on the list for closure before the heavy lift of installing Rule 562 on the core of the old 4-track "Main Line" begins. One loss that's easy to overlook is the now vestigial limited speed triangle at DOWNS interlocking with those at BRYN MAWR likely the only set remaining outside of Canada.

Another loss will be the intermediate signals at Exton, which were easily accessible from the SEPTA parking lot and well positioned for photography. 

For persons desiring photos of these, the Milepost 29 signals or what's left of DOWNS, you probably have until August 7th assuming transition operations will take place overnight. At 1:30pm on August 8th, THORN's final staffed shift will end. The tower is directly adjacent to the Happy Day's Diner for anyone looking to mark the event. 

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. 

Twilight of ATS on the Raton Pass Route

It wasn't long after ETMS PTC systems had been commissioned that the railroads using the older IIATS system went on a tear to decommission the old upside-down canoes. Most notably affected were the CNW-North and Northwest commuter lines operated by METRA, large parts of the ATSF Transcon in Arizona and Missouri and the Amtrak Surfliner route between Fullerton and San Diego. Apart of the NJT RiverLINE, which uses the IIATS shoes as a magnetic trip stop, the last main line use of IIATS is on Amtrak's Southwest Chief route between Albuquerque, NM and La Junta, CO. 

Since BNSF yeeted IIATS off its main lines in 2021, the status of ATS on the Raton Pass route has been somewhat "indeterminate". IIATS had been in service on New Mexico Passenger Rail Authority owned track between Albuquerque and Lamy, NM and as of 2025 the shoes were still in place minus some contraction at the southern end of the territory. Fixed IIATS shoes were also present on the BNSF owned Glorieta Sub to protect specific curves with full ATS territory present on the Raton Sub between Trinidad and La Junta, CO. Imagery shows that the BNSF territory IIATS shoes were also still in place as of 2025.

One might recognize the Raton Pass route as hosting the dwindling number of main line semaphore signals as well as the last main line Wig Wag. That is because the only regular traffic on this stretch of track is Amtrak's daily Sunset passenger train. As a result the route is both PTC exempt and at the absolute bottom of BNSF's priority for capital improvements or even basic maintenance. So while the ATS inductors were still in place it was plausible that the requirement for its operation had been removed along with the rest of the Chief route. Fast forward to 2026 when I noticed this Amtrak delay report for May 12th's westbound Southwest Chief.

3(12) with engines 167 and 14 with 225 customers onboard was delayed departing Chicago Union Station account mechanical was working on loading issues with engine 14. 3 departed Chicago 17 minutes late at 14:42. 3 was further delayed account being stuck in penalty on M1 at CP Roosevelt just outside the station. Mechanical responded to the train, the train maintained HEP. Mechanical initially resolved the issue and the train departed but was soon stopped again in penalty. Mechanical then bad ordered engine 167 and instructed the train to shove back to Union Station. Mechanical responded to the station to replace the ATS shoe on engine 167. The train departed Chicago a 2nd time after an additional 1 hour and 57 minute delay. 

So yes, IIATS is still in service on the Raton Pass route and leading locomotives on Amtrak's Trains 3 and 4 are required to have ATS equipment. A quick check has shown that the new ALC-42 Chargers do not lead on the Chief for this very reason (they were not built with such an old school protection system). Unfortunately Amtrak has filed a petition with the FRA to discontinue the system at least on the BNSF Subdivisions. The reason cited is a lack of 90mph running as opposed to the more typical PTC replacement excuse.

Even when the petition is granted it is unclear if BNSF will bother removing the inductors or clipping wires in the signal cabinets since they don't really get in the way. It is also unclear if the NMPRA (RailRunner) will retire its ATS system at the same time or if that system is even used by anything other than Amtrak trains 3 and 4. 

One final mystery is what happened to the IIATS system on the Raton and La Junta subs in the mid 2000's. In that time speeds on both subdivisions dropped from 90mph to 79mph (the non-ATS equipped national rail speed limit). However all or part of that ATS territory was still in place up to and including the present day (2026). If the track class was downgraded from 5 to 4, it's plausible that use of 79mph instead of 80mph is just a reflexive tic for the BNSF rules department. However I had also been informed that ATS had been "taken out of service" on these line segments despite the fact the timetables had ATS in service. If anyone knows please leave a comment, but if I had to guess BNSF may have started skipping some testing requirement necessary for the speeds greater than 80.

Asymmetric Tri-Lights

 When one thinks of the North American tri-light signal configuration (circular target with the lamps clustered in a triangle) one might assume that if the lamps are not set in a single large housing they would consist of single lamp modules kit bashed into a triangle instead of a vertical stack. For the most popular color light signal modules, the Safetran CLS-20, this is the case, however over the years the industry has produced some modular tri-light designs that don't use a common lamp module.

Of course I was prompted to write this post after being confronted by a tri-light product from our old friends at L&W. Purchased by Amtrak for its New Haven to Boston "Shore Line", this tri light has a single lamp module at the bottom with a double lamp cast aluminum housing above. From the front it looks like three singles due to the characteristic gap in the middle, but closer inspection reveals the true configuration.

 

 

The second example is from Transcontrol, a company typically associated with active grade crossing equipment. Somehow they were part of the contract to re-signal Hoboken Terminal around 1984 and their tri-light solution involves two standard lamp modules above an extra large one, which I assume serves as a junction box for the whole assembly. (Note, until this post I was unaware that Transcontrol made signal hardware and I might follow up with them in the future if more information presents itself.) 

One might consider the crop of asymmetric tri-lights to be offshoots of the original US&S style "TR", which features a single cast iron housing with three individual lamp sockets. Signals need terminal blocks to connect the interior wiring to the external wiring and terminal blocks take up space.

If you're wondering how the CLS-20 does it, there are openings on top at the 11 and 1 o'clock positions that match with other openings at the 7 and 4 o'clock positions. For a tri-light configuration the lamp modules are mounted 4 to 11 and 7 to 1. A supplier who can handle both vertical and tri-lights with a single SKU is naturally at an advantage so as a result the asymmetric tri-light has faded into history.

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.

PHOTOS: LANDIS - The PRR Main Line's Forgotten "Tower"

One might wonder how the electrified PRR Main Line could have an interlocking tower somehow more "forgotten" than the small booth that occasionally managed the emergency crossovers at LEAMAN, but it did and that forgotten tower also began with the letter L. LANDIS tower, in Landisville, PA, was always a stepchild of an interlocking forced on the PRR by the rival Reading Company by means of the Reading and Columbia Branch.  This was a forked "milk run" line connecting Reading (via Sinking Spring) to Ephreta, Columbia and Lancaster. The Lancaster fork was ultimately integrated into the west end of CORK interlocking, crossing the main line via crossover switches and the Columbia Branch via diamonds. The Columbia fork met the PRR Main Line about 8 miles to the west at Landisville and, due to the lack of any existing infrastructure, the diamond managed to justify its own interlocking tower, built and operated by the PRR.

Given the telegraph code NV, a square wooden tower was built in 1902 in the contemporary PRR style exemplified by the preserved LEMO tower at Strausburg. 

This tower lasted into the post war period, its Victorian aesthetic somewhat in conflict with the electrification infrastructure. In this photo one can see the Reading alignment complete with Reading style US&S color light signals in a target configuration. Also note the Reading freight station which in this photo is partly obscuring the PRR Landisville freight station behind it. 

Based on the 1962 interlocking chart it can be surmised that the old NV tower was taken out of service around 1953 with the block and interlocking station moved into the old PRR freight house. Here the part-time operator would work the crossing as needed using a 5 lever US&S table type interlocking machine. Each main track had a pair of signals controlled by a single lever in the US&S fashion. The Reading was controlled by lever 1, the PRR levers 6 and 8. The Reading signals could display Stop, Clear and Restricting in both directions. The PRR signals had a full ABS head with a Stop and Proceed marker with the current of traffic and a dwarf with Restricting and Sop against. The Reading track had split point derails on either wide of the diamonds controlled by lever #4 and the PRR had a hand throw trailing point crossover unlocked by lever 5. The last detail of note was an 'E' marker on the eastbound PRR track which would illuminate if the dragging equipment detector near milepost 79 were activated.



As of 1954 LANDIS was listed in the timetable as an Interlocking Station open part time from 8:30 AM to 4:30 PM daily except Sundays and holidays. By 1971 this had changed to 10:00 AM to 6:00 PM Daily except Saturdays, Sundays and Holidays. Ultimately the Conrail merger of 1976 would prove fatal to the diamond crossing at LANDIS as the Reading branch line was no longer providing "competition" in the Lancaster market and Conrail trains based out of the PRR Lancaster yard could serve what on line customers remained. Therefore the diamonds were removed, the "tower" was closed, the milepost 74 ABS signals replaced the controlled signals on the PRR Main Line and a PRR freight delivery track was repurposed into a new connection to the ex-Reading branch towards Columbia, PA.

Like many legacy railroad structures along the Amtrak RoW, the freight station version of LANDIS was boarded up and left to become somebody else's problem. 50 years later the building still stands in decayed-yet-reasonable condition.

Similar to the Reading's old Chester Creek Drawbridge, the 5-lever US&S "table interlocking machine" is still present in the operator's area, albeit in a stripped down condition. Similar to the single story PARK tower, the windows were covered over with high security wire mesh.

The "table interlocking machine" was a modular platform for very small interlockings up to about 10 levers. Each module contained a standard US&S bell-crank type "lever" and was could interface with both mechanical and electro-magnetic interlocking components. At LANDIS the lever modules have been removed, but the robust metal base remains in place.

For comparison here is a similar table interlocking device set up in NORTH PHILADELPHIIA tower as an auxiliary to the main US&S EP machine. 

 

We can see that the LANDIS machine had a US&S/S&F style mechanical locking grid as well as make/break circuit spindles.

As an interlocking station the operator was provided with a full telecom suite mounted just outside of the bathroom nook.

An old relay hut sits across the tracks, although it is hard to tell what era it came from, Amtrak, PRR or PC.

LANDIS continued on as an ABS signal location until the mid-2000's Rule 562 re-signaling. Today only those with a knowledge of PRR Main Line history, or a sharp eye for abandoned rights of way, would notice that something had once gone on here.

Just goes to show that while many old towers have been demolished, a few are still hiding in plain sight.

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.