SEPTA Suburban Trolley Signaling: Past and Future

Light rail is currently the locus of signaling innovation in North America due to its mix of limited regulation, low budgets and legacy systems.  For example I have previously written about DART's three different signaling methods in use on its light rail network. In Philadelphia, one such legacy system is the suburban trolley lines running out of  69th Street terminal on the western Philadelphia border. Similar to Pittsburgh's south hills light rail lines in concept, the method of operation is currently being converted from a basic trolley era ABS system, to a hybrid CBTC system.  As I just managed to pick up a bunch of new photos, I figured it was a good time to cover both systems while they are still in the transition period. 

Route 101/102 block signals at 69th St

The ABS system inherited by and later updated by SEPTA as necessary, was a 2-block affair with signals displaying proceed (green) or stop (red). Although there was one location, Drexel Hill Jct, that could be described as an interlocking with full signal protection and a power operated facing point switch, the entirety of the Routes 101 (Media) and 102 (Sharon Hill) were run under traditional ABS rules with hand throw crossovers and spring switches entering sections of single track. 

Two aspect ABS signals at a Route 101 hand throw crossover including operator hut.

 
The single track segments were handled with an automatic tumbledown scheme and the one junction was fitted with a three lamp signal and a route selection punch box. Where a diverging move was encountered a yellow signal indication would be displayed. There was also no ATS or ATC enforcement of signals or speeds. 

Legacy yellow diverging aspect at east end of Route 101 single track segment.

Due to the sections of street running and close spacing of stops, the Suburban trolley LRV's are considered to have sufficient braking performance to dispense with an Approach type indication. Signals are approached prepared to stop and when the next block is cleared, the following movement will get a clear signal to proceed. Not all of the route miles are protected by signal indication with the street running and other slow areas working on sight. These sections are partly defined by "end of block" signs. 

Route 102 switch protection signal paired with a single track block entrance signal.

In addition to the two lamp ABS signals, there are/were switch position indicators and reverse direction protection for the single track sections and Drexel Hill Jct. When entering single track and exit signal would follow the spring switch to protect against a race condition if two opposing trolleys were to attempt to "seize" the single block at the same time. 

Route 101 single track switch signal with block entrance signal in distance.

Starting in 2019 work started on a new CBTC based signal system that would also make use of sizable number of interlockings to replace hand throw crossovers and single track spring switches. As of early 2022 the CBTC system had not yet entered service so the interlockings were used to supplement the existing ABS signal system. 

New SEPTA Suburban Trolley cab display unit with CBTC disengaged.

In fact on the combined section between 69th St and Drexel Hill Jct there were sufficient interlocked crossovers to supplant all of the ABS signal locations! As many of the ABS block signals have so far remained on the routes past Drexel Hill Jct during the transition period, it is anticipated that the CBTC will provide full block separation, not just a safety overlay.

New Route 101/102 combined trunk interlocked crossover and block section signal.

All in all the project involved the addition of 10(!) new interlockings, three crossovers on the combined Rt 101/102 trunk, Drexel Hill Jct, one crossover on each Rt 101/102 branch, three Route 101 single track endpoints and one Route 102 single track endpoint. In addition to these interlockings, three additional holdout signal locations were installed in proximity to an interlocking.

New interlocked holdout signal at entrance to Rt 101 single track territory to accommodate short turns

Another interesting new feature is the provision of a yellow fixed ATS transponder adjacent to each fixed absolute signal.

Yellow ATS transponder located between mast base and rail.

Although I was unable to observe every detail of the current operation it appeared that the new wayside interlocking signals were backwards compatible with the old ABS system displaying R - Stop, G - Clear, Y -Diverge. The presence of a 4th lamp hints at at the presence of a lunar white indication that will either be used for a "cab speed" (most likely) or an absolute block / restricting signal.

Same location as above prior to rebuild with spring switch and yellow "end of block" sign indicating start of line of sight operations.

Although the new CBTC/CTC system is modern and high tech, it never the less exhibits the limits of technology to deliver substantive performance gains. Ten new interlockings along with 20 or so miles of CBTC will cost more to maintain than the legacy ABS system. Furthermore, the speed control function will almost certainly decrease performance from current standards. On the other hand contingency operations will be greatly improved with track work becoming possible during operating hours and vehicle/overhead line failures now able to be worked around without the need for temporary block operators hand throwing switches. In theory the capacity of the system will improve, especially on the route 101/102 combined trunk, however the decision to run more frequent service has always been limited by the budgets and political will of both SEPTA and various levels of government. My assessment is that operations will say the same, liability will decrease along with speed and the impact/cost of contingency operations will decrease enough to offset the high cost of the new signaling system, at least until the point that the technology becomes unreliable.

Death by 1000 Cuts: The NYCT Subway Slowdown

 Starting in the 1990's, the New York City Transit Authority (NYCTA) started a process to slow down the largest subway system in North America, ostensibly in the name of safety. Over the next two decades the process, conducted slowly and out of public view, went from costing riders a few minutes here and there to triggering a full on capacity meltdown as the system, despite its decreased performance, benefited from record ridership. Transit Twitter and Blog personality Uday Schultz has recently completed an exhaustive history of the great slowdown and the science of transit speed control in general. It's a great read and starts with a zero based explanation of the NTCYA's trip-stop and timer based ABS signaling system up through the events that triggered the management action and the subsequent slide into dysfunction. Still, while this piece does a great job explaining why, it comes up a bit short explaining "why". So lets dive in a bit.

One shot GT timer signals added to CANAL ST interlocking before re-signaling.

In the early 2000's everyone in the NYC Subway fan community was aware of the performance decreases and would track how the NYCTA seemed to seek out any location where trains could get moving and just find ways to throttle service back to a plod. Even in locations with no infrastructural changes the trains were operated with an appreciable lack of urgency. The community was full of theories as to why this slowdown was happening and, to a lesser degree, why nobody seemed to care. After all other cities, even those with traditional signaling systems like Philly, Chicago and Boston, found ways to achieve brisk acceleration and top speeds of 55-70mph, making the 25mph crawl of the NYC Subway a distinct outlier. 

SEPTA Broad Street Subway Express train @58mph.

As Uday's article covers (read it now to avoid spoilers), the speculation the early 2000's fan community was both right and wrong at the same time. They were right in that most of their theories were correct.  They were wrong in that there was no one reason that bore primary responsibility for the problem. The newer equipment, up through R68, did have slightly better performance than those the signal system was designed for. The new composite brake shoes did have slightly worse performance than the old iron shoes. The system did rely on train operator rules compliance and related management thereof to ensure safety. Then, between 1991 and 1995 all of these factors combined in varying degrees to cause four significant accidents, opening the NYCTA up to both liability and public pressure.

Inbound Williamsburg Bridge ramp with carlength long grade timer blocks.

The response was similarly multi-pronged from slowing rolling stock down in both acceleration and top speed (55 to 40mph), ubiquitous use of intermittent speed control devices, curtailment of restricted speed operation and harsh punishments for trip stop engagement. Much of this action plan was implemented over a period of 20 years so casual riders didn't really notice the decline in performance. The cherry on top was that the intermittent speed control devices were then allowed to drop below posted thresholds making operators wary of even trying to follow the posted speeds. This is what caused the opportunity to get a skilled operator and a "good run" to vanish over the course of the 2000's, especially as the pre-90's workforce that learned to run trains without speedometers, gradually retired. 

All of this background leads to the real question, why did ostensibly high level management decide that such a drastic decrease in performance was acceptable? This is important because in an age when getting the public to *want* to choose public over private transport, the performance of public transport is increasingly throttled by policy leaving private transport as the only option that can attempt to offer speed and convenience. Well, lets put on our 1991 hats and see what management may have been thinking.

1. The most salient factor was the long term plan to equip the NYC Subway with a full time ATC/ATO system, later realized with the selection of CBTC to replace the wayside signals, timers and trip stops. Investment in an end-of-life signal system would be wasteful and performance decreases could be argued as temporary.
   
   
2. After peaking at 2 billion annual riders in 1948, the shift to non-urban living and private transport dropped ridership by over half with the peak of NYC's crime wave coinciding with the subways trough of ridership. The system was running at half capacity so "slightly" increasing trip times was likely not seen to be a big deal.
   
   
3. Decades of disinvestment had caused the NYC Subway to fall into a prolonged state of bad repair. With limited funds compelled trading performance for safety.
   
   
4. The threat of continued accidents was a political liability while small overall changes in performance would be unlikely to generate much if any notice let alone political pushback.
   
   
5. The reliance on operator skill presented not only the continued risk of accident, but would also put up pressure on costs as said skilled workers had to be trained and retained. Uniform operations according to the speed control systems would make operators fungible and require a lower skill floor.
   

These 5 factors could be arranged multiple ways to create a compelling policy proposal to management. It would have taken an extraordinary amount of personal risk for any of the top officials to insist on maintaining performance standards when CBTC was right around the corner anyway. I think the decisive element was the NYC Subway consistently running at half capacity for over two decades. It's not even that signal system capacity *could* be reduced with little impact, but that the 900 million annual ridership seemed to be both a floor and generally baked into the city. If local New Yorkers were willing to risk their life to ride the system, an extra few minutes wasn't likely to deter them either. To some extent management was proven correct, their slowness campaign only became a problem after ridership doubled over the following 20 years.

If you want a take away its that reducing performance has, is and will be the go-to fix for even rare safety problems. We've seen this with PTC and we've seen this on other transit systems like SEPTA and WMATA. The changes are rarely publicized and the public rarely objects even as they unconsciously sour on rail transit and make the switch to private vehicles. After the service meltdown NYCTA did set up a speed improvement task force that has been fixing the mis-calibrated timers and raising speeds that were subjected to overly conservative calculations. Still, while the rollout of CBTC has allowed for increased performance profiles, it would be interesting to calculate if they match what was achievable by human operators working under a system with a slightly greater tolerance for risk.

PS: An interesting comparison can be had with how the UK responded to the Ladbrook Grove Rail Crash of 1999. The crash program to install TPWS at select locations was similar to NYCT's system-wide modifications, however as far as I can tell, it had minimal impact on train operation, perhaps in part of the UK's continued reliance of train drivers' compliance with rules to ensure safety, as opposed to technical mechanisms.

NYCTA CBTC Plan to Prioritize Closing Main Line IND Towers

 I just wanted to share a little info graphic put out by the NYC Transit Authority about its upcoming re-signaling plans.  In summary, due to ridership decreases due to COVID, the TA is no longer going to focus on CBTC as a capacity expansion tool, but as a cost reduction tool and will therefore be targeting its remaining un-resignaled lines on the IND, specifically the 8th Ave (A)(C)(E), 6th Ave (F), Fulton and Crosstown (G). These segments have pretty much all of the remaining single interlocking towers with either GRS Model 5 or US&S Model 14 interlocking machines.

Now, my tower list is from 2019 and I haven't been closely tracking NYCTA tower closures, but at risk interlocking machines include Model 5's at 30TH ST, 42ND ST NORTH and 42ND ST SOUTH on the 8th Ave Line, UTICA AVE, BROADWAY JCT, LAFAYETTE AVE and HOYT on the Fulton Line, YORK ST on the Houston Essex Line and NASSAU AVE on the Crosstown Line, as well as Model 14 machines at JAY ST on the Prospect Park Line and BEDFORD-NOSTRAND on the Crosstown line. Likely also affected would be the NYCTA's first GRS NX machine at EUCLID ave, but likely not affected are yard towers or the COURT ST transit museum tower. The Model 14 at PARSONS on the (F) is of currently unknown status as that section is currently undergoing re-signaling right now.

If you are looking to get a glimpse of some living NYCTA interlocking machines, the Model 5's on he Fulton Line are visible from the ends of the platform with UTICA AVE and LAFAYETTE AVE on the outbound platform and BROADWAY JCT on the inbound platform. 

I am currently planning an NYC trip for Mid-October and will attempt to check in on these locations.

FTA 2013 CBTC Case Study, With Takeaways!

It's time for another government document hiding in plain sight! This time we have CBTC case study from 2013 that covers the NYCTA 2003 L line project and SEPTA's 2005 Subway-Surface trolley tunnel project. You may recall my often cited MBTA study that determined that CBTC was not cost effective compared to coded track circuit cab signals. This document's primary goal is to explore the derails of each project and determine what lessons can be learned, however it does reach the conclusion that both projects reached their goals and were worth the investment. That might sound like an endorsement of CTBC, but a careful read of the document paints a more complicated picture. Yes, CTBC works, but should it be the preferred option? Read on to see my enumerated list of takeaways. 

1. Both SEPTA and the NYCTA had their own specific reasons for adopting CTBC and the paper does not bother to evaluate those reasons. From the point of evaluating the paper's endorsement of CTBC, the paper does not do much to actually compare it with the alternatives, especially from a cost basis. It basically says, NYCTA wanted to do X, CTBC allows for X, NYCTA is now able to do X, CBTC works.
   
   
2.  The paper reveals why the NYCTA and SEPTA chose CTBC systems and the answer might surprise you! SEPTA wanted a trolley tunnel ATC/ATP system and got one free as compensation from AdTranz for late M-4 cars. The NYCTA needs to be able to run both equipped and unequipped trains in mixed service. I suspected that the issue was the NYC Subways extensive use of single rail track circuiting and I was mostly correct in this regard as trying to install a jointless audio frequency track coded circuit system on top of a single rail track circuit system would require some costly hardware "hacks" as opposed to less costly software hacks.
   
   
3.  Cybersecurity is a ticking time bomb for CBTC systems. For both SEPTA and NYCTA "A complete description of the necessary security measures for the product over its life-cycle was not included in the System Safety Certification Plan." Even if best practices were followed when the systems were installed in 2003-2006, they have almost certainly aged out (think SHA-1 or RSA 1024). Both systems communicate on the 2.4Ghz WiFi band using a deterministic spread spectrum technique to avoid interfering with WiFi. Wireless message integrity on SEPTA's system is provided by CRC checks (not secure) and "authenticity" is provided by header formatting and train ID (also not secure). It is highly likely that tools could be created that could interfere with operations, although human operators would mitigate potential impacts.
   
   
4. The paper confirms that the the pre-2003 L line capacity was 20tph under DT-ABS/ATS and was raised to 24tph under CBTC with a possible increase to 26tph with traction power upgrades.
   
   
5. The L line re-signaling was contracted for $217 million and SEPTA's trolley CBTC was valued at $24 million. No effort was made to track down cost overruns, the cost of alternative signaling or the cost of debugging the CTBC.
   
   
6.  Both systems were indicated to have experienced 1-2 years of service impacts due to debugging issues. SEPTA's were noted as "significant". As of 2013 SEPTA's CBTC outages were pretty rare, however a trolley needing to cut out CBTC and operate manually via traditional ABS happened about 5-6 times per week. It was mentioned that SEPTA desired additional degraded service modes for the future Rt 101/102 install as "cut out" and "crawl" were insufficient.
   
   
7.  SEPTA's system was intended as a safety upgrade only. It did not increase or decrease capacity, nor did it save money due to the retention of the fixed ABS as backup. The capacity standard was 60tph.
   
   
8. The number of maintainable items is as high as ABS systems. Long term maintenance was not addressed, nor long term availability of proprietary parts. Note, parts for cab signal systems are still available from multiple vendors. If the original vendor cuts off support it may force another round of re-signaling, raising CBTC lifecycle costs.
   

I had been generally aware of all these issues before I found this paper, but they had all come from first hand experience and unofficial sources on various forums. I encourage you all to read the paper and leave your takeaways in the comments.

BART Going with CTBC

 You might have missed it due to COVID news coverage, but back in January 2020, whomever it is that runs BART decided to use some new taxpayer funding to replace the "50 year old" audio frequency cab signal system with CBTC.  While BART does indeed have some extreme capacity constraints funneling 4 lines down a two track trunk between Oakland and Southern San Francisco, as that very city has seen with its MUNI Metro Subway, CBTC is not all its tracked up to be.

This is being brought to you by the same team that sold a $400 million combination railcar and re-signaling package to the Baltimore Metro. Hitachi purchased the Italian railcar manufacturer Breda and the Italian signal provider Ansaldo, which itself was the parent of Union Switch and Signal.  I guess because Hitachi figured that Japanese engineering was better than that of Italy it has gone in with a full re-branding even though I doubt any of the actual work is being carried out in Japan. Like the DC Metro, BART has a core system that is approaching 50 years in age and likely was looking at a full signal equipment replacement similar to that which WMATA carried out after the 2009 signaling related collision.  Although BART has seen many expansions over the years, its core system was and likely still is based on GRS relays and Wee-Zee bond technology. 

 While BART may be hoping for those 30 trains per hour, the reality will likely be less as at a certain point trains become dwell time limited.  It's not that passengers can't all shuffle on and off in 30 seconds, its that they will likely not do it reliably and even a small disruption at peak capacity will result a standing wave traffic jam.  Hopefully, because Bay Area, there will be some sort of backup system as you know every wanna be hacker looking to make a name for themselves will be looking for ways to disrupt the system and anything that uses wireless is ripe for disruption.  If cab signal circuits will remain in service as a backup or on outer portions of the system where such equipment is not life expired, remains to be seen.  The BART system was already pretty useless to railfan with dull signals and rolling stock hostile to look ahead or behind views.  The new D type cars were posed to reverse this trend so get your photos and videos of the current signaling and train control before it vanishes.

MUNI Metro Subway - Unrealized Capacity

You may have read about MUNI's radical attempts to deal with congestion issues in its Metro Subway that runs under Market Street and also included the Twin Peaks Tunnel.  Long story short, MUNI is eliminating one seat rides downtown for riders on the J, K and L streetcar lines.  The given reason is since the J and K lines are limited to single unit LRV operation, those "slots" in the Metro Subway are being underutilized and the new operating plan will replace the one LRV trains with two LRV trains. 

The Metro Subway is signaled by a loop antenna based CBTC system in the style of LZB and if you are noticing a pattern between articles addressing CBTC and capacity problems then I thank you for being a long time reader.  Basically MUNI is noticing the capacity problems that stopped both SEPTA and MBTA from realizing a full CBTC fantasy in their respective trolley subways and MUNI's response is to make many commutes much worse.  To be honest this isn't just a CBTC problem as coded track circuits would have been no better and possibly worse.  The issue is a fear of less automated operation.

Here is an LRV on the eastbound track at the Embarcadaro terminal station, which seems to be the major capacity constraint as M, L, K and J line trains all turn back here.  You might notice a line of cones and a lot of unused platform space.  That is because at every Metro Subway station, only one train can platform at a time, even though the platforms are long enough to support two trains.

Here is the westbound track with a fresh train sitting behind the cones just hanging out with a second train close behind while they wait for the single loading/unloading berth to become available. On all of the Metro subway stations it is common for following trains to stop short on the platform and wait for the single loading zone to become available.  It is also common for passengers to run their buts off along the platforms to reach said single loading zone from the far end.

Both SEPTA and the MBTA use multiple berths at underground trolley stops to varying degrees.  For example at Juniper St there is an unloading spot and a loading spot.  At other stations different routes can stop at different points along the platform.  On both systems the signaling system is equipped with R/Y station signals that allow operators to creep forward and occupy the station behind another LRV.  It's not a cure all, but it helps. 

MUNI plans to update its CBTC system to one that uses wireless instead of loop antennas.  It might work better, it might not, but with new LRV's already arriving, maybe someone should have thought outside the box and ordered a radar based collision avoidance system to allow closer spacing in stations and thus pipeline the passenger boarding operation.  Once headways drop below two minutes, dwell time and terminal capacity dominate block separation.  It's why expensive CBTC systems don't move the capacity needle much and often do worse than traditional systems with on-sight operation, spring switches and loops.

High Impedance

An often overlooked issue with railroad (or transit) electrification is the conflicting requirement to use the rails for traction return current and to divide the truck up into electrically isolated segments for the purposes of track circuit signaling. Installing insulated joints between substations would either cause the electric vehicle to not go or would force the return current to find other transmission paths, most of which are usually not intended to see electrical current flow and might not be too happy about it either.

The right hand rail is insulated at the track circuit block boundary, the left is not.

Your first option is to use the one rail or 1+1 system.  Here you have one rail with insulated joints creating track circuit blocks and the other rail acting as a common ground without insulated joints.  One downside is that only the insulated rail gets broken rail protection.  There are probably other downsides as well as this method was only used on some of the oldest electrified transit systems such as the NYC Subway.  Another option is to have a 4th rail system like the London Underground where traction return current uses a dedicated 4th rail instead of the running rails.  The better option is to use a device called an impedance bond to have both isolated track circuit blocks and a traction return path via the rails.

Here we see a Union Switch and Signal model impedance bond, patented in 1922.  I am not sure if there were any earlier models of bond or if this was used on the 1915-1918 PRR and New Haven 25hz electrification projects before the patent was granted, but it would have been available for the major waves of electrification that took place in the 1920's and 30's.  An impedance bond is a type of isolation transformer where traction return current can pass with low impedance (impedance is the AC version of resistance), while track circuit current faces high impedance and thus follows the path of least resistance through the track circuit logic. The necessary trick to making this work is to have track circuit current at a different frequency than the traction return current.  For example DC traction current with an AC track circuit or one frequency of AC return current with another frequency of AC track circuit. 

In the above diagram from a Japanese Wikipedia page we can see a slightly more elaborate setup for an impedance bond.  The two coils connected at the center tap are what constitute the impedance bond.  The secondary windings capture the AC track circuit current via the magic of induction and feed the signal logic.  More typically the bond omits this secondary winding and the signal logic is fed directly from the rails.  Remember this is a super high level summary so for more detailed technical information please consult Google or your reference library.

Here we see two of the 1922 patent US&S bonds and their modern Siemens replacements for use on Amtrak's NEC.  Amtrak, like the PRR before it, uses 25hz traction power and 91.66hz coded AC track circuits.  Normally the coded track circuits would operate at 100hz, but as a multiple of 25, return current harmonics could be detected as track circuit current, which is bad.  91.66hz is close enough to 100hz to be cross compatible with 100hz electronics.

The spec plate on the new bonds show the Amp rating for traction return current and the impedance values for 100hz current (400 ohms) and 60hz current (2.4 ohms).  While 25hz isn't listed I am assuming that the value would be in an acceptable range. A DC traction system sees much higher amp loads than an AC system and therefore the bonds must be much larger with thicker windings to handle it.  Systems with both AC and DC, like Penn Station, would use DC rated bonds.



 Of course the story doesn't stop there.  In the late 1960's the rail signaling industry introduced the concept of jointless track circuits for use in transit applications.  These make use of AC frequencies in the "audio" range of 1-5 kHz.  These higher frequencies attenuate after a much shorter distance and using a mix of frequencies one can have a given track circuit receiver able to hear the signal from a single specific transmitter.  Still there is the issue of the pesky traction return current that needs to move between the rails, to ground and NOT into the signaling logic.  The solution was the Wee-Zee bond (trademark of GRS) that creates this path to ground while preventing the track circuit signal passing between the two rails.

In this close up of a US&S "Minibond" on the Chicago El, we can see the the listed transmit-receive frequency pairs, the cab signal code frequency and the DC power rating (3000amps at 0.00003 ohm).

Now if you like Technology Connections, here's an interesting one for you that revolves around the necessity of impedance bonds.  Europe is currently under the thrall of axle counters for train detection as opposed to track circuits.  Why would the normally safety conscious Europe in interested in a train detection system that doesn't positively detect the presence of a train (or flood or broken rail)?  Because the Central European 16.66Hz electrification club, which includes Germany, Austria, Switzerland and a few others, electrified their rail systems were those systems were still operated using non-track circuited manual block signaling.  When upgrading to automatic block signaling, installing track circuits would require installation of impedance bonds and related electronics.  Therefore an alternative, axle counters, was sought out and adopted.

Likewise, the NYC Subway is moving to Communications Based Train Control instead of the audio frequency track circuits as their use of the one rail system would require the installation of who knows how many Wee-Zee bonds.  Just goes to show how technical decisions can be highly path dependent.  Keep that in mind the next time you have trouble figuring our the logic behind that might not make complete sense. 

SEPTA Signaling Updates

I just compiled a few bits of signaling news after my recent SEPTA Winter fan trip and figured I should share them while they were still fresh. The the headline is that the work to rebuild or change ARSENAL interlocking is already having a negative impact on signaling as the 20 exit signal on #4 track at the north end of ARSENAL has already been replaced with what I assume is a temporary color light mast exit signal.

I say temporary because a few feet to the north some new turnouts had been installed either for an Amtrak connection (unlikely) or some sort of relocation of at least one of the Airport Line ladders off the curve where they currently exist.  Anyway, the 20 auto and southbound ARSENAL home signals are accessible for photography and a definitely work a hike in combination with the PLs at CP-WALNUT north of the University City station.

I finally got out to The SEPTA Norristown Line terminus at Elm St in Norristown and saw that SEPTA put a fair amount of money into the interlocking making all the switches power operated as well as adding power details.

Southbound signals were of the Unilens type, despite the signals well known problems. 

CTBC transponders have made an appearance on the Routes 101 and 102 suburban trolleys.  The existing ABS signaling system is a two aspect type with fairly long blocks, however after the trouble SEPTA had and continues to have in their downtown trolley tunnel I'm surprised they didn't consider just switching to some sort of light rail CTC.  I suspect they want to tie in light preemption and other goodies.

Anyway, those are the major changes I noticed.  Hope you had a reasonable 2019 and let's all look forward to a better 2020.

CBTC is a Scam and the MBTA Backs Me Up

Communications Based Train Control promises higher capacity at lower costs thanks to the magic of WIRELESS TECHNOLOGY!  However almost every real world situation that makes use of it seems to wind up costing a ridiculous amount, having major reliability problems or both.  It turns out that with signaling there is no free lunch, but when faced with overcrowded subway trains, planners can't help but get seduced by those lovely braking curved.  I mean fixed block, that's so 1890, surely we can do better!

In 2016 the MBTA was conducting a capacity study for the Red Line, which currently has a somewhat anemic throughput of 13tph in the peak period.  With new rolling stock on order, the (T) would literally have more cars than it could run.  The current signaling system made use of fix block audio frequency cab signals installed in the 1980's.  This is similar to many other transit systems such as the CTA, WMATA and BART.  Of course CTBC is the to go technology for capacity expansion and the study quickly confirmed this.  Oh wait, it didn't.

• A detailed analysis assuming a moving
block CBTC system on the Red Line was completed.

• Analysis found that a CBTC system would produce
an improvement of just one train per hour beyond
the improvement from the new cars and minor
system changes.

• Major Red Line capacity improvements can be
achieved without implementing very costly CBTC. 

• Long dwell times in the downtown area and close
spacing of stations limit CBTC as much as they
limit fixed block systems.

That's right, just like the costly NYC Subway L Train CBTC system only increased capacity by 2 trains per hour, applying CTBC to the Red Line would only improve capacity by 1 train per hour over a fixed block alternative.  Past a certain threshold capacity is limited by dwell time and the efficiency of terminal interlockings. The study also found...

• The shorter the block length, the closer the
system is to the ideal CBTC (moving block)
braking distance

• MBTA block lengths in the central subway already
average less than 500 feet (6 car trains are 416
feet long)

It's nice to see that for once a transit agency actually ran the numbers and decided that CBTC just wasn't worth it.  It turned out the best way to increase the capacity was simply to allow the new rolling stock to use updated braking curves that will result in later braking and more aggressive cab signal speed stepdowns.  Also the 1980's audio frequency cab signal system will have its components replaced with digital versions that have faster reaction time and thus allowances for less conservative block progression.