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.
Since I last visited THRON interlocking on Amtrak's Harrisburg Line, more progress has been made towards rationalizing the interlocking and closing the tower. Similar to what has taken place at PAOLI, redundant crossovers and stub tracks have been removed, although it is still not clear what the final outcome will be as SEPTA service looks to expand back to Coatsville and Parkesburg.
As recently as 2019 THORN was still in an approximation of its 1970's configuration with a 6-track full crossover and stub tracks for the old Trenton Cuttoff, removed track #3 in both directions and the #6 yard track. You can see my video post on an operator setting up a typical SEPTA R5 local movement across the entire plant.
However since then Amtrak has removed the worst of the redundancies with the 53 turnout and 55 crossover being completely removed, the 49, 51, 57 and 61 crossovers being reduced to turnouts, track #3 being removed in its entirely along with most of track #6 and the through section of track #5. Perhaps most significantly the interlocking has been completely converted to electric point machines, despite new A-5 point machines being installed on the #41 and #43 crossovers in 2019. You can browse the current state of the interlocking here.
Elsewhere on the pneumatic front, OVERBROOK interlocking has seen continued attrition of its A-5 point machines with as few as 3, the #11, #15 and #19, remaining in service. The casualty list includes the 019 switch in the former Woodbine section of the plant.
After PAOLI's conversion a few years ago, this leaves ZOO interlocking as the only intact pneumatic interlocking plant on the Harrisburg Line.
While getting photos around the JO section of ZOO interlocking I noticed some interesting writing on the A-5 pneumatic point machine attached to the 131 switch.
In stenciling the signaling department appears to have labeled the point machine as a "bastard". Someone else, perhaps another employee, perhaps a local, has expanded upon this with "/whore". Given that the points appear to show evidence of a recent rebuild, it is possible that this A-5 has been assembled from the parts of others or contain a non-standard modification. I believe that A-5's have a notion of handedness that could be at play here. If whatever the modification was not entirely successful that could have resulted in the editorial comment.
I had the opportunity to get some rear window time on Amtrak's Eastbound Pennsylvanian and although the last of the position light signals vanished nearly 4 years ago, a few scraps of history linger on. First amoung these is MG Tower located between Horseshoe Curve and the PRR summit at Gallitzin. Targeted for demolition in the summer of 2020 (along with the nearby AR tower), it has nevertheless held on due to its remote location and linger asbestos issues.
Another surprise was that artifacts from the 1970's era re-signaling west of Johnstown also survived the 2018 re-signaling blitz. Specifically the relay and air compressor houses. The air plants in particular date from the PRR interlocking tower era. I was able to capture many of these air plants when they were still in service and some also contained 100hz power supplies for the signals.
The line segment between CP-C in Johnstown and CP-SO in South Fork was the last bit resignaled under Conrail in the 1997-1999 time frame and it appears that NS retained the late model Conrail era relay huts, outfitting them with new Conrail blue Signal Indication Point signs.
Also in this segment is the stump of AO tower that also served air compressing duties up through the early 2000's, long after control had been passed to C tower in Johnstown during the PRR period. We also see that CP-AO, in service on track #1 has also been supplied with a SIP sign covering the ABS cab signal location in service on tracks #2 and #3.
Finally I can confirm that the entire Altoona terminal between CP-ALTOONA and CP-ANTIS remains under Rule 261/CSS operation instead of cab signal only operation. The sole main track automatic signal is located at CP-HOMER for the non-interlocked track #2.
I've frequently pointed out the impacts of Positive Train Control on train performance in general. While not technically inherent to the requirement, they are an inevitable consequence of policy and implementation choices. These include things such as stacked safety margins, overly conservative performance assumptions and locations tracking uncertainty. While the ACSES system used by cab signal equipped railroads in the northeast is generally superior to the wireless data based ETMS used by the class 1 freight railroads, certain ACSES implementations have continued to demonstrate the performance problems I identified almost a decade ago. Recently I was able to capture a concrete example of one on video.
Here we see an NJT Morris and Essex train led by ALD-45 #4510 entering Newark Broad St station on Track #2. The 4E signal for BROAD interlocking is immediately east of the platform end and the eastbound train gets hit by a positive stop about 700 feet (6-8) carlengths short of the signal location. Instead of being able to complete its station work as the signal system was designed to allow, the train sits off the platform for over 2 minutes, adding to the delay.
ACSES implements its positive stop feature using a two step process. First a fixed track mounted beacon that transmits other permanent speed and positioning data will inform the onboard system that the train is approaching a positive stop. Next, if no cab signal code is detected , the onboard system will enforce a positive stop by calculating a 0mph stop point based on its super conservative assumptions of ice covered rails and a train with cheese in place of brake pads. The train stops up to 1500 feet from the signal and, well, the current policy is to wait there. The initial concept was for crews to use a stop release procedure to creep up on the signal, a feature implemented by specific freight railroads using ETMS, however most most if not all northeast commuter railroads have taken the CYA approach and just let the trains sit several hundred feet in advance of the signal, even if that means being unable to platform.
Supplementary ACSES transponders at Valley Stream
Apart from stop release, one alternative mitigation is to add additional ACSES transponders that can reduce the location uncertainty. The LIRR has installed two additional sets at Valley Stream that sees the same problem with platform-end signals, although I have heard this can still stop trains 1 or 2 carengths short of the stop point. A quick look at the overhead shows that NJT has not implemented this mitigation at Newark Broad Street. Another mitigation is to set the stop point to the legal requirement of the fouling point of the first trailing point switch or diamond. At NJT's BROAD interlocking this point is about 1 carlength beyond the 4E signal. Finally, they can be more realistic about the performance of the equipment.
Just like the New York City Subway a decade ago, its always safer to cover ones ass than to fight for performance in a post-pandemic transit landscape were trains are running half empty anyway. If NJT feels like it is looking at service cuts, investing in capacity makes no sense.
I know I'm a couple years late on this news, but ATCS (Advanced Train Control System) radio relay that replaced pole based code lines for Centralized Traffic Control schemes is in the process of changing frequencies (or just being completely phased out) due to an FCC directive that will reallocate its 900Mhz spectrum for wireless broadband in 2025. For the last 20+ years ATCS has been super useful for enthusiasts to monitor railroad dispatching in real time as data packets are relayed from station to station, just like with an old CTC code line, only now they can be sniffed and displayed.
Although some railroads like CSX shifted away from ATCS in favor of satellite links years ago and hard links like fiber optics were popular for a window in the 80's and 90's, ATCS has been a massively useful took for those looking to take photos of trains or just gather data that can be used for all manner of public policy. Word is that for those railroads wanting to keep the ATCS system, the data will piggyback on the frequencies allocated for PTC communications. However because the PTC communications specifications have to be purchased for a sizable amount of money (who'd have thunk it), the ATCS monitoring community is facing a reverse engineering challenge.
The silver lining could be that after some amount of outage, the community will be able to monitor not only lineups, but also PTC signaling and authority information.
Seems like my blog has been having an impact on some state highway departments based on some of the innovating new road traffic signal indications I have been seeing lately. For example I that Diverging Clear has been one of the more common "non-standard" highway signals for a while now, but in New Jersey I found an example of Approach Diverging!
And if that doesn't get your cab signals flipping, while in Maryland I caught an example of another popular new highway signal indication, the flashing diverging arrow, which I assume is either an alternative to R/Y→ Diverging Approach or perhaps some kind of Slow Approach 🤔
This is a somewhat new development after the appearance of flashing Red arrows which is some kind of Diverging Restricted Proceed 🤷. Anyway, who knows what they'll think of next? Perhaps something with flashing green. 😏
Unlike previous generations of automatic train control, the on board PTC software has as much if not more to do with the operational impact of the safety system than fixed infrastructure like code rates and block length. In the case of ACSES, Amtrak's PTC implementation, track mounted transponders conveys data about upcoming civil speed limits, grades and positive stop points and it is up to the on board system to develop a braking curve. In theory this curve should represent the maximum braking effort the rail vehicle is capable of if tripped by the PTC system to prevent an unsafe level of overspeed. The concept of a penalty brake application exists for thus purpose as a full on emergency application requires some additional inspections. (Although I have been present when the "freight" ETMS PTC system threw my Amtrak train into emergency.)
Four years ago I benefited from a SEPTA training run to capture two videos of how their PTC implementation functions and the braking curve was ridiculously bad. Granted I lack similar curve information for other operators, but the SEPTA engineer could stay under the curve with a very mild brake application. I got some comments on the order of "PTC is new and SEPTA will inevitably made modifications to improve the performance." Well on my most recent winter SEPTA fan trip I lucked into another training run on the Airport Line and I can report that the system has not been changed and it still causing significant delays.
Unfortunately I was only able to capture video of the cab display unit returning from the Airport to Eastwick which had no PTC speed downgrades and therefore no demonstration of the braking curve (although I did capture a missed transponder reading). In fact my inability to get a video angle was doubly unfortunate because the braking curve is so conservative that it caused the engineer to trigger a penalty brake application just north of PHIL interlocking's southbound home signal. This is where the line speed of 45mph transitions to 30mph for the Airport Line curve just south of PHIL interlocking. (Even before ACSES this curve was protected by a 45mph Approach Medium cab signal) This meant that the on board system calculated a braking distance of about 4500 feet to slow from 45mph to 30mph.
Time for some math. The starting velocity is 66 fps and final velocity is 44fps. From my observations the braking "curve" is linear which gives us an average speed of 55fps and thus a deceleration time of 81 seconds. This lets us solve for acceleration with a solution of 1.38fps^2 or 0.9 mphps, which is an absolutely pathetic braking rate. Even if I assume I was wrong about where the speed curve kicked in and the penalty took place just after the limits of PHIL interlocking, 2800 feet from the restriction, the resulting deceleration rate is still 1.4 mphps, less than half of the design acceleration rate of 3 mphps.
In this example we have the two bugaboos of PTC working together to sap performance on what should be a speedy trip to the airport. The first is a stacked safety margin. The older ATC system enforced a 45mph limit on approach to and around the 30mph curve. That would have been a rough ride and close to the overturn speed, but would likely be enough to prevent a derailment without getting in the way of the engineer. Today the ACSES takes the 30mph as gospel even though that figure already accounts for human error. Next, the conservative braking curve compels a speed reduction about three times farther away than would be necessary with the full braking force available. The end result is net gain of 10 seconds to traverse the same 4500 foot distance and you can see why this is a problem. 10 seconds isn't much. It's certainly not enough for anyone to fight for or risk being blamed for if something goes wrong. unfortunately this 10 second loss happens again and again and again over the course of a run with the end result of SEPTA having to lengthen scheduled running times by an average of 4 minutes across all of its lines. Add in more small delays like low maximum speeds, long dwell times, slow terminal operations and voila, rail transport is uncompetitive with private road transport.
As you can see in the above video SEPTA cares very little about speed in general. As seen in the video about, the R1's 4-station airport terminal complex has blanked Restricted speed limit, even when approaching CP-AIRPORT JCT after passing a wayside automatic distant displaying Approach Limited. Why even bother with the wayside at that point! Prior to ACSES, SEPTA had plans to use the 4-speed cab signaling system to implement rapid transit style signaling when Rule 562 operation was installed on its Reading territory. Maybe we'll see a realization similar to NYCTA's that speed improvements, even small ones do matter. Or maybe we'll see the response to poor post-COVID ridership to be service cuts.
