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.
For years concerns of PTC interoperability drove all manner of decision making at freight and passenger railroads. For example's CSX decision to isolate itself from SEPTA's Regional Rail network, NICTD choosing not using the cab signal codes present on its line because Metra Electric wanted to use the freight-centric ETMS and MARC dumping ACSES for reasons. However one common thread is that when push comes to shove, equipping locomotives with multiple PTC systems is not a big deal (although it certainly isn't free).
Case in point are the SD60E locomotives that are always leading certain Norfolk Southern intermodal and manifest trains traveling on its New England Bridge Route between Harrisburg and Ayer, Mass. Between Harrisburg and Sunbury its on ETMS, then its off PTC entirely all the way to Binghamton. Then it on CP's ETMS all the way to Mechanicville, NY. From there it hits the former Boston and Main which is again PTC-less, but at Wachussetts it enters MBTA territory which uses Rule 562 cab signals and ACSES the last few miles to Ayer. These SD60E's are dual equipped for PTC and ACSES and although less needed on the NEC due to Amtrak dual-installing ETMS, they found a new home on this run. If I ever get close to one I'll see if I can get a photo of the antenna.
Anyway, I heard that due to the shift of NS New Englande route internodal trains to the former Conrail Boston Line, this unique PTC situation will soon be obsolete as manifest freight might terminate at East Deerfield or something. If you're a fan of oddball leading equipment quirks, get your photos while you can.
Since my last update on the status of the former Pennsylvania Railroad Harrisburg Power Director's Office a surprising amount of progress has been made to get the equipment functioning in its 1943 configuration. For those of you who might not be aware, the Harrisburg Power Office used a relay based SCADA system to remote control all of the 1937-39 westward extension of the 12kv 25hz electrification network that first began operation in 1915. The second phase of the PRR's electrification from New York to Boston had largely relied on tower operators to directly control the substation equipment via local control boards in the towers (although some substations may have been staffed 24/7 themselves). Although remote control SCADA equipment was installed in some towers and the Baltimore power office, the expansion of electrification west of Paoli, Morrisville and Perryville to Harrisburg and Enola would be under the purview of a single office in Harrisburg with a code based remote control system.
The office was in service using most of the same equipment from 1939 through to 2013. When the Harrisburg Chapter NRHS took over the space in 2022, it was still in roughly the same condition it had been in when the doors were locked 9 years before. Known for their preservation work at HARRIS tower, including a fully functional and completely interactive Model 14 interlocking machine, the Harrisburg Chapter had its work cut out to achieve a similar level of interactivity for the Power Director's office. Based on the amount of time it took to restore HARRIS, my own personal estimate was on the better part of a decade. Therefore you can imagine my surprise when I learned that a good chunk of the active equipment had already been restored to functionality in only 18 months. In fact the video below records the moment I learned that the office relay logic had been hooked up to an Arduino mimicking the field stations.
Because the third phase of PRR electrification was financed with depression-era WPA loans, the PRR had to spread the wealth and contract half the system to Westinghouse and half the General Electric. Westinghouse and its Visicode scada system is the simpler of the two to reverse engineer and debug (one can send digits with a literal rotary phone) so currently it is the Westinghouse half of the equipment that has been wired up to modern digital logic simulating the field stations. The General Electric equipment uses a more complex protocol that requires another round of development, but that is not insurmountable. Interestingly the Westinghouse equipment was largely used on the low grade freight lines that last saw service in 1981 when Conrail discontinued its electrified operations. Therefore that equipment came back to life not after sitting idle for 10 years, but for 40 years!
The large display wall has also been restored to mostly full functionality, however compared to the SCADA consoles this functionality was somewhat limited. The indications on the display show switches being open (green) and closed (red), as well as the use of white lights to show de-energized track segments. These are wired to reflect the position of switches on the SCADA consoles or on the operator's consoles where remote operation is not in effect. Therefore the board is more of a visualization device than a real time status indicator.
The longer term plans for the office are still under consideration. The equipment is a bit less interactive than a railroad interlocking machine with active train movements, however there are quite a few scenarios that can be played out including routine operations, breaker trips, transmission line problems and current load issues. Whatever the case may be, I'll be sure to report on it here.
METRA recently announced that they were looking to raise speeds on its electric division from the current 65mph to 80 or even 90mph. Typically this is the sort of project that justified a 8 or 9 figure capital spend with concrete ties and brand new signaling. However this announcement explained that management simply looked at the facts on the ground and concluded there wasn't actually anything precluding those faster speeds. Apparently the entire operational management of METRA has assumed that the 65mph figure was a fundamental limitation of the current ABS/CTC block signaling distances that were laid out with the electrification programme in 1926. In reality those speeds and signaling distances were tied to the braking profiles of Pullman-built heavy weight MU cars that were built for the "new" electrified service at the same time. Management had simply neglected to update its prior assumptions both time the IC/Metra Electric fleet was renewed.
To be fair to Metra, in 1972 a "stopping distance" related crash between heavyweight and Highliner stock killed 45 people probably made Illinois Central management less enthusiastic about making the line faster, especially when 1926 Pullman stock was still in South Shore Li8ne service. In 1983 when the last of the old cars were finally retired the IC Electric division was run under contract to the Chicago Regional Transportation District (later branded as Metra) with with Metra formally purchasing the line in 1987. The accident plus the delayed retirement of older equipment and topped by the contract operation and then change in ownership goes a long way to explain why the electric district speeds stayed unchanged through two equipment replacement cycles, however the problem of sticky speeds isn't unique to Metra and bedevils rail operations across the United States.
Back in the day railroad operating speeds were a somewhat nebulous concept. The number one limiting factor on how fast trains went was fast they could go. Often the timetables would only list restrictions with everything else left to the skill of the engineer because, except for a few crack passenger locomotive classes, in the age of steam trains just didn't go that fast (and the fastest trains had the most experienced crews). It was the 1948 ICC rule requiring ATS for speeds 80mph and higher that was the harbinger for the formalization of railroad speed limits that took place in the 1970's and 80's. Objective regulated standards replaced the judgement of railroad superintendents in areas of track geometry, signaling and, most recently, grade crossing warning time. Railroads tended to get a bit of pass on what was already in the rulebook or in service so they were ok as long as they didn't try to make anything faster.
This is now we have things like the old RF&P being a 70mph railroad while the adjacent "A-Line" is an 80mph railroad despite both being run by CSX to approximately the same standards. Raising those speeds require expensive consultants to dot all the i's and maintainer hours to adjust all the grade crossing equipment, all to say a few minutes for trains the freight owner doesn't run. Passenger operators like METRA are also not immune as the inevitable grade crossing or trespasser strike will have lawyers pouring over any recent decision to raise speeds. Long story short management will see little benefit from raising speed, but assume a great deal of professional and institutional risk. The exception lies in cases where significant amounts of money are available to rebuild a line to make the speed increase effectively free.
Fortunately as we have seen with the NYC Subway and now with METRA's electric division, transit management seems more willing to take on the risk to improve performance. SEPTA in particular is notorious for its 1930's vintage speeds set to match the performance of heavyweight AC MU cars.
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.
