CTA Skokie Swift Smackup

In November 2023 an inbound "Skokie Swift" Chicago El train rear-ended an MoW vehicle stopped on the track waiting for signal clearance into the Horward terminal interlocking complex. The impact took place at a speed of 26mph and the NSBT was quick to blame "outdated" signal stopping distances that were last set whenever cab signaling was installed on the line, likely in the 1970's or 80's. The result was a multi-month service suspension and a reduction in maximum authorized speed from 55mph to 35mph, which was achieved by disabling the 55mph cab signal code at ever block location. To the lay person this might seem open and shut, the CTA did something wrong and they fixed the problem. In reality this is a classic example of go slow safety scolds and risk averse CYA officials pushing people away from public transport. This case is especially ironic since when the Skokie Swift opened in 1964, it was a demonstration project on how rapid transit could be high tech, modern and fast compared with the "square cut gear" era equipment.

For background, the CTA uses a pretty standard audio frequency cab signaling system with automatic speed enforcement and speed codes for 15, 25, 35, 55 and 70mph. Lack of code is fail safe and registers 0 mph and it is standard practice on this type of system to have sufficient 0 code behind any train for fail safe stopping. While most of the Skokie Swift is straight and uncongested, allowing for 55mph operation, the the busy Howard terminal will frequently see Skokie trains encountering stop signals and thus need to reliably slow from 55mph to 0 starting at a point about 2500 feet from Howard Interlocking's home signal. This would be carried out by progressively slower cab signal codes, although it is not clear if the operator gets a 0mph code ahead of the wayside absolute signal or at it, where a physical trip stop is also provided. The following CTA produced head end video of an inbound Skokie Swift run shows how this progression from 55mph to stop is well within the vehicle's performance envelope. The 55 to 35mph code change point is encountered at 7:55. Code change points are identified by small black boxes, called impedance bonds, located between or adjacent to the rails.



Feel free to judge for yourselves, but it appears that the first code drop is just before the hand throw crossovers about 2500 feet before the Howard absolute signal as stated in news reports and the last code drop is located under the overpasses at the final curve. It is not entirely clear if the final drop is to 0mph and the train takes the time shown to react and stop (likely) or if the operator chooses their stop point on a more favorable 15mph code (possible) or even if a timer that drops out the code mid-block is involved (unlikely). (Note: It's pretty trivial to determine how CTA trains get stopped before absolute signals by observing the cab signal display in the cab from the first car, I just haven't done so in a while so let me know if the comments.) The difference between normal operations and the day of the collision was the presence of an MoW snow melting vehicle on the inbound main track about 370 feet short of the Howard interlocking home signal. Had everything been working as intended, the train following the MoW vehicle should have gotten stopped before the final code change point under the overpasses.

The NTSB's knee jerk assessment implied that the following train somehow couldn't get stopped in time. As in it got the proper speed codes, but the speeds and distances were calculated incorrectly and it ran into the snow melter. Given that the line has been operating without incident for 60 years this seems unlikely, however the train was a newer 5000 series car that has only been operating for 15 years so it is possible something like crushed leaves resulted in decreased braking that combined with a heavier vehicle could have resulted in the observed accident. Still, is there an alternative explanation?

What stands out to me is the impact speed of 26mph. That's pretty much full speed approaching the final code change point. Typically when stopping distances have gotten out of sync with the equipment you see the rail equivalent of foot faults where the train can't quite get stopped in time. Remember in this case, if the block before Howard interlocking is occupied the second to last code change point should be giving a 0mph. It's almost like the train was approaching the MoW vehicle like it wasn't there. Moreover the operator indicated that the signal system commanded a speed reduction from 55 to 25 or 35 ~2100 feet from the equipment (or ~2500 feet from the Howard signal). If you refer to the video you can see the train begin to slow from 55mph at that same point, but again, that is for an unobstructed block before the Howard signal. If that block was occupied the inbound train should have gotten a signal drop one block before.

By this point I've already given away the twist. Maintenance of Way vehicles and other things the FRA likes to classify as "track cars" are known to not reliably shunt the track circuit and therefore need to be run with absolute block protection, especially to the rear and double especially when cab signals are involved. In cab signal territory if a track car fails to properly shunt the track circuit, not only will it not be detected by the signaling system, but favorable cab signal codes can also be transmitted to trains approaching from behind. Rail contamination like leaf debris only makes this problem worse.

 

To be clear, I have heard stories of trains having braking issues and sliding past calculated stop points as a result. For example an Acela locking up its wheels approaching Trenton and sliding for over 2 miles allegedly resulted in an extra block of speed control being added. Still, every detail about the indecent matched up with a loss of track circuit shut involving a track car and an approaching Yellow Line train that received cab signals in the sequence expected for a stop at the Howard interlocking home signal. It's certainly possible that the signal design created some grossly unsafe condition as the NTSB is implying, but the decades of safe operation imply otherwise. Unfortunately signal distances are easy to calculate and in addition to using the worst possible braking performance and the worst possible rail condition, the NTSB might actually believe rail vehicles need to emergency brake short of any obstruction they encounter within the range of vision.

Caught on Camera: Mendon, MO Level Crossing

 One side effect of taking photos from the back of long distance Amtrak trains is that from time to time you get a good shot of what might end up in a national news story. When the Mendon, Missouri grade crossing accident and derailment first took place in the summer of 2022 my impression was that it was located at a random farm crossing in the middle of nowhere. Since the former ATSF main line lost its searchlight signals over a decade ago there was no real need to check on the status of a notable signal such as this Conrail era signal that almost got wiped out in an Columbus, OH area derailment.  

Anyway, while watching the above Plainly Difficult production on the incident, I spotted what appeared to be a signal location adjacent to the collision site on County Road 113. Checking the archives I discovered a clear photo of the accident site along with the Milepost 363 intermediate signals taken from the rear of the Southwest Chief in 2013.

In addition to the signals and the unprotected grade crossing we can also see the ATS inductors that allowed for 90mph speeds across the state of Missouri. These had been recently removed by the time of the accident due to PTC making the legacy system unnecessary.  Anyway the moral of the story is to take photos of everything because you'll never know what might be historically significant.

Position Light Contributor Chris Meadows Killed in Hit and Run

Due to anonymity concerns I don't usually get to name the platoon of contributors who help me with my information gathering operations.  Other times they are simply friends or family I am able to browbeat into going on a photo mission for me.  One such friend was Chris Meadows and although he was not at all a railfan or rail industry professional, when IU tower in Indianapolis was faced with impending demolition, Chris went out of his way to get me some photos for no other reason than I asked.

This week Chris was killed by a hit and run driver in a fat tired Bro SUV  while biking around Indianapolis.  Although not a rail enthusiast Chris preferred public transport and bicycle transportation and was a consummate urbanist.  Chris' passion was reading and writing and had been a long time contributor to the e-Reading news website Teleread.org.  I made his acquaintance years ago in a fiction group and the work and enthusiasm he put into his interests was a positive force in the lives of those around him.   Chris and I have different hobbies, but we both engaged in non-market driven, hyper niche reporting because if we don't do it nobody else will as all the real money seems to be in promoting conspiracy theories 😢

Unfortunately I didn't get to use the photos Chris got for me back in May of 2019.  I figured I was going to do an "IU Tower Demolished" post, but the event happened without fanfare or demo photos and they just sat on my drive.  Nevertheless they are still an important part of the historical record so I am sharing them below.

 

 

The last days of IU, May 2019

2020 has been a very challenging year for a large number of reasons.  If there is one takeaway it's keep yourself safe.  If you're taking some risks getting some rail photos, keep your head on a swivel.  If you're following all the rules riding your bike downtown it's not going to stop some dude bro from rolling coal right over you.  Stay alert, be prepared, have a plan and let your friends and family know how much you care about them.

 

Pittsburgh Line Cab Signal Overlaps and Human Factors

A recent derailment between three NS freight trains near Labrobe, PA sent me down the rabbit hole of human factors and accident prevention once again.  The derailment was the result of a restricted speed rear end collision that caused cars to derail into the path of a third opposing freight train.  Straight away I would like to point out that this sort of accident is not PTC preventable and exactly the reason  why high crash standards are important even in the face of technical safety systems.

Occurring just a few months after NS changed the Pittsburgh Line from Rule 261 wayside signaling with Cab Signals to Cab Signals without fixed automatic wayside signals I immediately suspected that the loss of visual cues from wayside signals prompted a crew to misjudge the point where Restricted speed would take effect as under the traditional wayside system an obstruction can be located one foot beyond the signal displaying Restricted Proceed.

 In theory a cab signal should change from Approach to Restricting as one crosses the insulated rail joint into the block where the cab signal code is not reaching the following locomotive.  It is standard practice for a cab signal cut to be placed some distance in advance of an absolute signal, dropping the cab to restricting in time for a train Approaching at Approach to know that an absolute stop is necessary.  I have observed SEPTA placing cab signal cuts in advance of automatic signals on the Reading viaduct, but there the signals are spaced a half mile apart so and SEPTA had plans to convert the Regional Rail Division to transit style operation anyway.  However, in doing some research I learned that Conrail had implemented this same system on its entire Pittsburgh Line with cab signal cuts between every signaling location such that a train on Approach would see its cabs drop to Restricting a mile before encountering the Stop and Proceed signal.  This feature has since been confirmed from a head end video.

New Signal Indication Point (SIP) at MP 125.3

Old unlabeled Cab Signal change point at MP 125.3

This explains why NS was creating new "Signal Indication Points" every mile along the Pittsburgh Line as part of its re-signaling project.  It wasn't increasing capacity by increasing the number of blocks, just replicating the system Conrail had already installed.  I have long wondered how Conrail would prevent rear-end accidents on its Rule 562 territory (cab signals without fixed wayside signals) as there were no mentioned in the rulebook of crews traveling on Approach being provided with a stop target (as is the case on the Union Pacific Hiawatha Sub).  It turns out that they were likely using signal overlaps the whole time.  If this practice originated with the PRR's Conemaugh Line experiment remains to be seen.

Of course when it comes to human factor's nothing is what it seems.  In a world where one's cabs stop to Restricting halfway through a block one knows to be clear until the next wayside signal, crews might not take that Restricting cab signal so seriously until passing a wayside Stop and Proceed.  Over decades of service, these habits can become ingrained, especially if rules testing fails to cover the corner case.  A feature designed to provide crews with advance warning of a track obstruction may have instead created a false sense of security and a hidden reliance on wayside signals.

Additionally, although this episode both revealed and in part confirmed the use of cab signal overlaps on former Conrail territory, it now raises further questions about how the new NS SIP system will function compared to the Conrail system of waysides and cuts.  Will the "odd" SIPs still only act as Approach -> Restricting cut points or will they be sully featured automatic signal locations that help to reduce train separation?  I guess I'll have to put my feelers out ;-)

Reading Line Runaway!

So a few days ago there was a runaway incident on the NS Reading Line.  If you had seen some of my previous photo sets on my other blog, this line had recently been converted from Rule 251  ABS to Rule 261 CTC so I have some photo coverage of the area in question.  The incident involved a tank car with 75 tones of paraffin, rolling out of an industrial siding and onto the main line, following the descending grade eastward into the Lehigh Valley.  At CP-BURN the runaway car was routed, either intentionally or by happenstance, onto the former LVRR routing towards Bethlehem, where it eventually slowed down enough in the Bethlehem yard area for an employee to mount it and apply the handbrake.

Diverging route at CP-BURN

The most amazing thing is that there is actually a video of the runaway car taken from the overpass at BETHLEHEM where an astute railfan was able to position himself based on radio traffic.  What caught my attention was that the dispatcher actually had lined a route through the interlocking plant and displayed a Clear signal indication to the wayward tank car!  (I guess because it can shunt the track circuit it didn't count as a track car ;-) ) It's also worth noting that the single car had no issues shunting the track circuit and dropping the signal.



The important take away is that despite the billions in investment, this situation was not PTC preventable as the runaway car has no operable brakes no any sort of digital electronic anything.  Good old track circuits and CTC gave the dispatcher the tools to detect the runaway and route it onto a safer route with no high traffic grade crossings, and the Railroad Safety Appliance Act of 1893 provided the grab irons for an employee to grab a hold of to then work the hand brake.

First Confirmed PTC Casualties

I have always maintained that PTC was going to kill people and not just in the sense that it makes rail transportation uncompetitive with highway travel.  Of course the assumed cause of these deaths would be a PTC penalty brake application on a long freight train in a mountain territory leading to a runaway.  Well I'll be the first to admit when I am wrong because the first PTC related deaths happened when an Amtrak train hit a mis-aligned hand operated switch at track speed due to a signal suspension facilitating a PTC-motivated re-signaling project. 

19th century technology reliably tells me the switch on track 2 is lined and locked.

What is really gauling is how the media keeps saying that PTC would have prevented the accident.  Well do you know what else would have prevented it?  A functioning block signaling system, with or without cab signal ATC!  This is probably a good harbinger of the other way PTC will kill people.  By making train crews reliant on an electronic crutch, the accident rate will increase when operating under contingency circumstances, like a signal suspension (or a run of the mill PTC outage).  Crews get used to the cab display warning them of that 30mph curve and when it doesn't, boom.  We've seen this countless times with Airbus' horrible human factors engineering that pretty much ensures that pilots will stall and crash the plane when the computer training wheels come off.

Bad Signaling at Bad Aibling

The Bad Aibling rail accident was a head on rail collision that took place on February 9th, 2016 on a single track portion of railroad near Bad Aibling Germany.  As of this writing the investigation is pointing towards human error on the part of the signalman and, more specifically, the fact that the signalman was playing a game on his mobile phone around the time the events of the accident occurred.  Now. while phone distraction has played a role in previous rail accidents, in this case I believe the true culprit is the design of the German railway signaling system itself and any claims of distraction are simply an easy answer.

This tower operator is distracted, but not unsafe

First let's deal with the issue of distraction.  Unlike operating a vehicle, operating a tower or dispatch interface does not require constant attention.  Of course it is better to have someone paying attention, but it is not unsafe and moreover, distractions are already built into the job.  Operators frequently have to use the restroom, eat meals, talk on the phone to other railroad employees or even leave the tower to deliver train orders.  In a job filled with distractions, the whole point of the signaling system is to prevent distraction from leading to accident.  It is a fundamental principal of railway signaling for things to fail safe.

German Zs1 Signal

The mechanism that allowed two trains to end up in a cornfield meet is the Zs1 signal, shown above.  Known as an "Ersatzsignal" or Substitute signal it is placed below a "main signal" and lit upon command of the signaler when the main signal cannot be displayed normally.  Many in English speaking rail circles have described it as a Restricting or call-on signal, but that analogy is not entirely accurate. In practice it is more like a manual block clear of the type that can still be encountered on the LIRR.  Trains pass the Zs1 and proceed through all turnouts at no more than 25mph and before they can increase to normal speed .  Some sources state the 25mph limit applies to the next main signal, but a majority say normal speed and that would agree with the behavior of the second train involved with the accident.

Zs1 Displayed for a train movement

 The Zs1 signal is displayed when, for any reason, the main signal governing movement into a section of track, cannot be displayed.  This can be due to a bulb out condition, an axle counter miscount or any other problem with the signaling system.  As far as I can tell, the Zs1 guarantees route locking only.  In most rail systems around the world, when the signal system fails trains must proceed on sight prepared to stop short of an obstruction or other problem.  This is because even in the case where the cause of the failure is known, that doesn't mean a second problem might exist.  Because the situation of compound failures can lead to accidents, in most of the world a substitute signaling system must replace the automatic one to relieve trains of this burden of traveling at Restricted speed .  As one might expect, performing this task can be quite involved, requiring multiple signalers and communicating the fact to many trains and qualified employees. However in Germany all it takes is a button press to light up the Zs1.

Bad Aibling Stellwerke

In North America there is no signal that can be displayed into a CTC block where traffic is set in the opposite direction in the same way a Zs1 is used in Germany.  You can't even give a Restricting against the flow of traffic, necessitating a permission past stop procedure and even then the train will continue to be limited to Restricted speed.  The permission past stop procedure involves speaking to the locomotive engineer, usually over an open radio channel.  Yes. dispatchers in North America can screw this up, but the procedure takes time, requires two persons and requires the operator or dispatcher to pay attention.  In Germany the signaler presses a button and the train operator heads on his way.  When used for routine problems like bulb out or axle miscounts the process can become rote and the procedure can be shortened or skipped entirely.

The Zs7 Caution signal is the best analog to North American Restricting

Unfortunately I don't as of yet know what the Zs1 procedure involves, but I from what I have read it consists of ensuring that the block is actually free of obstructions.  A newer signal, Zs7 Caution, is used in places where the signaler is unable to positively determine block occupancy and does in fact require the train receiving it to proceed at Restricted speed, but the problem of actually setting a route against traffic remains.

313 absolute signal where the Zs1 was displayed before the collision. Annotated version.

While misuse of the Zs1 was the ultimate cause of the accident, there were a number of other systemic factors that contributed to it.  First, closed channel radios are employed  in theory to prevent "confusion" over who is speaking to whom, but the end result is that train operators are kept in the dark.  Furthermore, in the case of the Bad Aibling accident closed channel radios actually prevented the signalman from being able to stop the trains involved with a radio call because he forgot the correct emergency broadcast code to use.  You know, as opposed to pushing transmit to talk.


Second, the use of axle counters as a cheap alternative to track circuits, only serves to further ingrain the manual block thinking.  Detecting track occupancy without track integrity only perpetuates the inability of distant signals to stop trains.  Moreover, while axle counters are prone to failure (or miscount), just like track circuits, the signaler is able to reset the problem on his own with a button, instead of needing a maintainer to fix it.  While some can see that as a feature, it removes a valuable form of two person control.  Again, fixing signal problems via the interlocking panel becomes habitual and eventually an accident happens.

Panel blocking was a basic way the PRR made operators think twice before bypassing signal protections.

Most signaling systems have their single point of failure.  In North America there isn't anything preventing an operator or dispatcher from giving a bad Form D and running a train into another on a stretch of single direction ABS track.  However for the last 50 years we have been on a quest to eliminate ABS and replace it with something where such a mistake cannot be made because the technology prevents it.  Germany however, despite all its fancy train protection systems, flank protection and signal overlaps, is still burdened with 19th century thinking when it comes to block systems.  As a society Germans are really good at following procedures so therefore these sorts of accidents are rare, but allowing something like the Zs1 still tempts fate and every so often you get burned.

Note: This is my 261st post.  Yay for important milestones!