Portland MAX Signaling Primer

In the 1980's and 90's North America's light rail renaissance didn't just save money over traditional urban metro systems by embracing street running and low level boarding. At the time, the signaling standard for "heavy" metros involved full CTC and cab signaled ATC, which came with both high infrastructural and operational costs. However light rail systems got a pass to re-write the rule book and adopt signaling practices that hankered back to the low cost interurbans of old with single direction operation and limited use of interlockings. While I have previously covered two examples of these low cost signaling practices in Denver and Dallas, I recently had the chance to explore a third in Portland Oregon.

Beginning operations in 1988 and seeing significant expansion in the 90's and 2000's, Portland's MAX light rail has the typical mix of downtown street running and dedicated suburban rights of way with operating speeds up to 55mph. The signaling of choice is single direction 3-aspect Automatic Block signaling using US&S transit type signal heads. There is little formal distinction between interlocking and intermediate signals each signal is the same in having a line-prefixed number plate.

One quirk of the system is the setup of having an ABS exit signal at each station and another ABS signal between stations. When a station platform s within a block, the signal will at best display yellow Approach so there is a distinct rhythm of exiting a platform on a Clear then entering the next on Approach. Intermediate signals on the main line away from stations are often of the high mast variety with earlier installations using US&S N type mono-block heads.

A key feature of the MAX train control system is the use of fixed inductive Automatic Train Stop (ATS). Unlike some other systems, MAX actually includes a bit of overlap to get trains stopped before they hit something. This is made possible by an LRV's enhanced braking performance necessary to handle the challenges of street running. Apparently MAX also has a few ATS based speed control timers that function independently of fixed signals, but are indicated by wayside signs.

Interlockings are limited to major junctions, yards and a few select crossovers. These are supplemented by hand operated temporary block stations. As I said before, both ABS and Interlocking signals are largely the same except for the possibility for route indications on the interlocking signals. This can range from the use of a single lamp in the "call-on" position, or separate heads, each governing a specific route. The wayside signals are supplemented by switch position indicators of the US&S ES-20 variety.

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.

BNSF to Retire Most ATSF ATS on 2/15/21

On Presidents Day 2021 (likely at Midnight between Sunday and Monday), in a move that was entirely foreseen and entirely understandable (unlike with the UP cab signals), BNSF will retire the Santa Fe era IIATS Automatic Train Stop system that was popular during the first wave of technical railway safety aids in the 1920's and 30's.

Bi-directional ATS shoes under a classic ATSF signal bridge on the Marceline Sub.

 The inductive system, similar to the magnetic Automatic Warning System in UK service, was identifiable by the upside-down canoe shaped shoes mounted to the right of the track.  When activated by a signal displaying an indication other than Clear, the shoes would trigger a warning horn in the cab and failure to acknowledge would result in a penalty brake application.  Set as the most basic requirement by ICC directive for travel 80mph and over after 1948, railroads couldn't abide by its modest cost, resulting in an unofficial nation-wide rail speed limit.  While the Southern, New York Central and Santa Fe maintained hundreds of ATS equipped route miles, all but the ATSF managed to abandon their systems around 1970 with the general collapse of passenger services.  For whatever reason, the ATSF Chicago to LA "Super Chief" route retained its ATS system, allowing the successor Amtrak Southwest Chief to travel for long distances at speeds up to 90mph. 

Inert "always on" ATS shoes protecting a permanent speed restriction on the Marceline Sub

A clever system that could fail safe with just inert steel components, IIATS was in service on the Marceline Sub across Missouri and the Needles, Seligman and Gallup Subs between Barstow and Dalies, allowing for speeds of up to 90mph on Class 5 track.  Unfortunately the system relied on careful clearances between the lineside shoes and the pickup coils, that were mounted, as needed, only on the head end locomotives on freights traveling this territory. Moreover, BNSF went out of its way never to expand the system from what they had inherited, therefore as tracks were upgraded to bi-directional operation, the ATS would remain in the old single direction ABS configuration. In other cases ATS was only in service in one direction on both tracks.  

ATS shoes for westward movements only on both tracks on the Seligman Sub.

The good news is that active PTC is being accepted by the FRA as a valid ATS replacement.  Moreover, in the affected areas since signaling, track and grade crossings are all configured for 90mph, speeds will either remain at 90mph or will be raised to 90mph where ATS did not cover specific directions of travel.  It remains unclear if previously non-ATS territory that is equipped with Class 5 (90mph pass, 70mph freight) track, will see similar speed increases. I have been informed that, similar to the METRA ATS shoes, the timetable for removal is 90-180 days.  However the BNSF ATS territory is probably 10+ times the total route territory, so we'll see.

Railrunner territory semaphore with ATS shoe on the Glorieta Sub.

Due to absent or incomplete PTC, ATS will remain on parts of the Glorieta (controlled by New Mexio Railrunner), Raton, LaJunta and Topeka Subs, however it has been all or partly suspended on most of this territory since the early 2000's, lowering speeds to 80mph where applicable. Due to the nature of how ATS works, I have been told that Amtrak Train 3 and 4 run with the system on, but do not report any activation issues.

ATS shoe on the NJT RiverLINE.  The only instance where IIATS is used as a trip stop.

In addition to the Chief route, ATS will remain in service, enabling 90mph on the former ATSF San Diego route, now playing host to Amtrak Surfliner Trains as well as on the NJT RiverLINE where the technology is used, shockingly, to enforce positive stops at absolute signals.  Anyway, get your photos (or after 2/15 get your ATS shoes) quickly because after President's Day, they could start to vanish without warning.

Chicagoland CNW ATS Retired

The Intermittent inductive automatic train stop system in service on two former Chicago Northwestern commuter lines was taken out of service on October 19th, 2019.  UP/Metra received FRA permission to abandon the system due it being generally rendered unnecessary through the deployment of PTC.   Known for its distinctive "upside-down canoe" track mounted inductors, the IIATS system was developed by General Railway Signal in the 1920's and at its peak covered thousands of miles of main line track with the New York Central, Southern and Santa Fe being the most prominent users with the system supporting high speed operation after the ICC 80mph regulation came into effect in 1948.

ATS inductors partly hidden in the snow below Metra UP-Northwest Line Signal 48.

 Although the Central and Southern dropped the system in the 1970's, the Chicago Northwestern installed ATS on the North line to Kenosha in 1952 and the Northwest line to Harvard in 1967.  The system provides a in cab alert if the train passes a signal displaying an indication other than Clear, which the engineer must acknowledge.  Although the system is no longer is service, removing the inductors has not been a priority and there was likely no alterations made to any signal logic as the greatest operational impact of ATS is the pickup shoe mounted to the leading truck of the locomotive or cab car.  The ATS shoe must be properly gauged to prevent false activation or damage as well as tested like any other technical safety system.  The immediate result of the October 2019 retirement was the removal of equipment mounted ATS shoes with the track mounted inductors slated for removal over time.

This means that there is still a window of time for fans to get out there and document the trackside component of the ATS system as installed by the CNW, especially on the Northwest line with its three track arrangement on the UP Harvard Sub.  At this point ATS is still in service on portions the former Santa Fe "Chief" transcontinental route between Chicago and LA, the Surfliner route between Fullerton and San Diego and the New Jersey Transit RiverLINE where it functions as a positive stop enforcement device at interlockings.  Currently UP is undergoing a dispute with METRA over operation of the former CNW commuter routes with UP looking to offload responsibility.  As the North and Northwest lines see minimal freight traffic, an outright sale to METRA could keep the inductors in place for many years to come.  The Southwest Chief route in New Mexico, Colorado and Kansas has the ATS system "out of service" for over a decade, but the equipment left in place due to general disinvestment in the line.

ATS inductors at CY tower in Chicago.

Left unresolved is the fate of the CNW Automatic Train Control two aspect cab signal system.  Although targeted for retirement by PTC, continuous cab signal systems have proven to be a more reliable form of wayside to train communication and the FRA is still generally in favor of ATC as a PTC supplement.  Union Pacific with its extensive network of traditionally cab signaled track, may look to convert the CNW system or keep it in place as the differences can be ultimately handled in software.

Surviving BNSF Marceline Sub Searchlights Retired

While this probably isn't breaking news I am still going to report the fact that the last two intact ATSF era signal bridges on the Marceline Sub in eastern Missouri were de-signaled in late 2019, some 6 years after the rest of the route was re-signaled in the summer of 2013.  The two-track, weathering steel I-beam construction signal bridges at mileposts 243 and 241 not only remained standing, but also retained their US&S H-5 searchlights.

MP 243 signal in 2013

MP 241 signal in 2013

These signals were located between Argyle and Ortho and also retained their prefab concrete relay huts.  As you can see from the above photos, PTC antennas had been erected and no replacement signals were on hand.  However, seeing that the signal heads on the bridge at MP 238 had been turned in place, I just assumed that the MP 241 and MP 243  signals would likely be replaced or removed in short order.  The replacement signals at MP 243 and MP 241 use 1 mast and one cabinet mounted half mast.  The ATSF structures were still standing as of April 2020 and as far as i am aware the few color light equipped ATSF signal bridges are also still in place.  My 2013 survey of this line segment can be found here.

Caught on Camera: ATS Ding

Intermittent Inductive Automatic Train Stop (ATS) was that thing that met the minimum safety requirements for high speed rail as laid down by the Interstate Commerce Commission in 1948, and although adopted by the New York Central, Southern, Santa Fe and others, was pretty much ripped out everywhere it could be after the end of most private passenger operations in 1971.  ATS soldiers on in those few places where it could not be so easily discarded, namely the former Santa Fe transcontinental Southwest Chief and San Diego routes and the former Chicago Northwestern commuter lines out of Chicago.  The latter two routes both feature bi-level cab cars where one can, in various degrees, get a railfan view and hear the going on in the cab, so it becomes possible for one to hear just what sort of alerts this safety alertness system produces.

METRA Up-NW Line Typical ATS Inductor Setup

Now I was expecting something similar to a British AWS activation horn, which is quite loud and designed to get the operator's attention.  However, when I reviewed my video, what I heard in METRA Gallery cab cars was small analogue bell chiming once. You might even need to replay the video a few times as you might miss it right after the train passes the Diverging Clear signal.



In this Amtrak Surfliner video you can hear a small electronic beep right after the passes a diverging signal at T=11:20 and an Approach Diverging Signal at T=6:55.  Again, very underwhelming.



These are just two examples of videos where one can hear the ATS ding, but they cover both types of equipment passengers can reasonably expect to hear a ATS activation from. I may post updates here if I find cab videos from other equipment.

Denver Light Rail Signaling - Checking All the Boxes

From time to time I have brought up some of the quirks inherent to North American light rail signaling systems.  Because they exist in a regulatory and cost grey area (not really railroads, not really subways, able to stop on sight in traffic, etc) the signaling systems they employ tend to be very economical.  Well this past summer I traveled to Denver and rode around on its extensive light rail network.  There I noticed that the RTD light rail had methodically checked off every box on the light rail signaling checklist and I figured I should share it here.

1.) Missing Wrong Direction Signals 

See that little red circle?  Yeah, that's plated as a signal because the RTD's commitment to single direction ABS is so complete that all wrong direction movements need to get talked past the stop disc at the next interlocking.

2.) No Distinction Between Auto and Interlocking Signals.

See any difference between the ID plate on the interlocking signals in the first picture and the ABS signal in the second?  No?  Well that's par for the course on a light rail system.

3.) ATS

Light rail systems don't uniformly lack speed and signal enforcement.  They just opt for the budget versions.  RTD Light Rail has some sort of loop based ATS on its main line sections, but the operators weren't too helpful in providing the details on how it worked.  Of course where ATS proves impractical one gets a nice little sign.

4.)  Single Headed Signals.



Light rail systems hate confusing drivers with multiple signal heads, so flashing aspects warn of diverging movements.

5.) Vehicle, Signal Thyself

Dispatchers cost money, so LRVs simply set their destination and let track mounted sensors do the rest.

6.) New Lines, New Rules

How can consultants bill those hours if they just say to stick with the same old thing?  Of course the line that just opened in 2017 would have some new signal rules requiring a second head!

7.) US&S N-3's

You look hard enough around a large light rail system and you'll find a US&S style N-3 signal head 😏

Did I miss any?  Throw something in the comments and I'll see if I can find an RTD example ;-)

Non-Conditional Cab Signal Drops

In the wake of the recent Metro-North derailment I wanted to share a few bits and pieces on non-conditional cab signal drops as a way to control train speed for non-signaling related reasons or to warn Engineers in advance of a particular hazard. While Cab Signaling or any kind of signaling is typically seen as a way to warn trains of dynamic hazards, there have always been cases where signaling has been employed as a tool to show trains for static hazards. Typically railroads have preferred to use line speeds for such static hazards as the regulatory issues and costs are much less. Case in point being equilateral turnouts where all routes get Clear signals and the restriction is listed in the employee timetable. However on speed signaled roads the most common use of signaling to control timetable speeds is seen with slow speed terminal trackage where all routes, straight and diverging, are signaled for 15 mph.

If one scours enough interlocking diagrams it is easy to find examples where what might meet the signaling definition of a "straight" or Normal Speed route provides a more restrictive signal indication in order to deal with a particular high risk speed restriction. One well known example was the former CP-WEST PITT interlocking on the Conrail Pittsburgh Line that retained its 15mph Slow Speed routes due to a sharp curve west of the Pittsburgh Station. Even after the interlocking was removed westbound trains still encounter an Approach Slow at CP-PITT or CP-EAST PITT before the MP353 automatic displaying Clear.

Signaled speed restrictions are certainly more expensive than signs or ink.

Technical signaling enhancements like IIATS and the British AWS both contained mechanisms for non-conditional activation, which had the benefit of being cheap to employ due to there being no need for attached power or logic in such situations. To this day there are a number of ATS protected speed restrictions on the former ATSF "Super Chief" route from Chicago to Los Angeles, even outside of ATS territory as locomotives on the route are generally ATS equipped.

1920's technology is sufficient to alert a drowsy Engineer.

This finally brings up the use of "phantom signals" or non-conditional cab signal drops to control train speed at high risk speed restrictions. I have heard this was employed in a number of locations by the PRR, but was unable to find any references for that, but the most notable use of this practice came from Amtrak in the result of the Back Bay Derailment in the late 1980's where a high speed Amtrak train approaching Boston at 100mph failed to brake in time for the sharp 30mph curve at the west end of the Back Bay station. As a result Amtrak agreed to install non-conditional cab signal drops at a number of "high risk" speed restrictions along the Northeast Corridor. These include:

* BAY Interlocking near Baltimore for southbound trains.
* Frankford Junction Curve outside Philadelphia for southbound trains.
* Elizabeth, NJ S-Curve for northbound trains.
* Boston Back Bay station for northbound trains.

Unlike a rapid transit system with some sort of hard ATC or ATO system where the speed is enforced through the entire restriction, Amtrak's method dropped a Clear (125mph) cab signal to an Approach Medium (45mph) signal and then lifted it after a distance sufficient for the Engineer to apply a brake application sufficient to suppress the Automatic Train Control system.

While other eastern commuter railroads such as SEPTA and NJT have installed similar "speed control" cab signal drops on their territories, Amtrak's did the best at getting the train to slow without sufficiently gumming up the works. For example SEPTA now has extensive cab signal speed enforcement in the area of JENKIN interlocking that goes beyond what is required by timetable speeds and NJT recently re-signaled the approach to the Delair Bridge with a non-conditional Approach Limited at the new JORDAN interlocking replacing what had been Clear signals all the way across the bridge and hitting trains with a 2-mile 45mph slow zone.

Anyway the real reason I brought this up was because I actually found a sweet video on YouTube showing a Metroliner cab car as it runs at the front of a Keystone train from Linden, NJ through the Elizabeth S-Curve. You can watch the cab signal drop about 50 seconds into the video and then pop back up about 30 seconds later before the train even gets within sight of the curve. Still, the speed has been slowed and the Engineer still has sufficient operational leeway to not lose time.



There is no reason that Metro North should not have adopted this practice sometime in the last 20 years for the clearly high risk speed restriction at Spuyten Duyvil. The northern limits of CP-12 are 0.7 miles from the curve and the southern limits 0.2 miles. A non-conditional cab signal between those two points would have provided ample warning to any drowsy engineer with room to bring the train to a complete stop if necessary.  I am sure MNRR will apply this "solution" both at the Spuyten Duyvil curve (and, I assume, the similar curve at New Rochelle) in advance of whenever they complete their PTC project, but keep in mind that the PTC project that will cost 300-500 million dollars on Metro-North alone would have been just as effective as the existing ATC technology if used properly. Why pay more?