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.

Velcorp Gems - A New Signal Supplier Enters the Fray

While out riding the new MBTA Green Line Extension I noticed a new corporate brand stenciled onto the back of a cheap looking transit type LED signal head.

My original assessment that  Velcorp is the company and GEMS is the brand name of their rail signaling equipment turned out to be incorrect as Velcorp was actually Virginia Electronic & Lighting LLC and GEMS was their subsidiary General Electronics Mechanical Services, which I guess does all the rail stuff? Anyway, as you can see below the product looks to be on the low end of the build quality scale with exposed nuts on the front, lots of hard angles and what appears to be a non-locking access door on the rear.

 

The mounting equipment is branded as Harmon, which may be doing business under the Landsay brand now. Each signal also has a pair of mounting brackets on the top that look a bit like owl tufts. From Velcorp's website it looked like they had previously focused on LED modules before suddenly getting the contract for the GLX wayside signals. Velcorp isn't local so maybe its a Veteran owned small business or something.

Despite their appearance, the signals seemed to work well enough. Still, I have not encountered them on any other transit system. Velcorp is one of several entrants into the rail signal space to have offered up products competing against the legacy brands of US&S and GRS (Alstom) who have the capability to make larger cast aluminum and iron housings.

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.

Line of Sight - DART's Third Method

Last year ago I wrote an article on how the DART light rail system in Dallas used two distinct signaling methods.  Automatic Block Signals with Automatic Train Stop  were used on the original Red and Blue lines built in the 1990's and audio frequency Cab Signals without intermediate wayside signals on the Green and Orange lines built since 2000.  However there is a third method first used on the initial segments and most recently employed on the Blue Line extension to Rowlett. This method is Line of Sight operation and while I had seen the signs, I did not fully learn what it signified until I recently had the opportunity to ride the southern portions of the Red and Blue lines that make the most use of Line of Sight.

Line of Sight territory is exactly what it says on the tin.  Trains must proceed able to stop short of any obstruction including other LRV's, pedestrians, motor vehicles, traffic lights, etc.  It is governed by the following section in the DART rulebook.

Line-of-Sight Operation: 

4120 Line - of -Sight Territory Incorporates mainline tracks not protected by ABS/CST. Line-of-sight territory incorporates the following:

• West Oak Cliff Branch - Zoo Station to end of line at Westmoreland Station.
  
  
• South Oak Cliff Branch - Morrell Station to end of line at Ledbetter Station. - Central Business District - Houston Street to Pearl Station.
  
  
• Rowlett - Signal G1813 to Rowlett Station 

4121 Line of Sight Speed Trains must operate at a speed which will enable the train operator to stop short of any obstruction. All special instructions or posted speed zones must be complied with. Speed shall be reduced when adverse operating conditions exist, (i.e.) poor weather. 

4122 Minimum Separation Trains must maintain a minimum separation of at least two LRV lengths unless authorized by the controller or when a train is stored in the tail track. a. No more than one train at a time in the same direction may occupy a city block in the CBD unless authorized by the controller.

When I first encountered Line of Sight Operation at the Garland station on the Blue Line it was accompanied by a two aspect signal that I surmised was part of a low cost go/no-go ABS signaling system.  From the overhead and street view I could identify other signal signals along the line and it seemed that LRV's would approach each prepared to stop within Line of Sight.

It turns out I was only partly correct as these Block Indication signals have their own alternate method of operation. On the two southern routes, Block Indicator signals can work in conjunction with Start Block (SB) and End Block (EB) signs.  Passing Block Indicator with an SB triangle the train is protected by track circuit block until the following EB triangle. I am not entirely sure if the SB is needed before any EB, but that seems to be how it was set up.

The Block Indicators are used where there are line of sight issues like curves and steep overpasses so that LRV's don't have to crawl on these stretches of track.  On the straight and level trains are able to travel on line of sight up to a speed of 45mph. This is of course quite safe as the LRV's are designed to run in traffic and have magnetic track brakes for bus like stopping. When exiting the ABS territory that proceed the Line of Sight territory LRV's receive an "Approach" class indication before the LoS territory sign.

SEPTA two aspect block signals on the Route 102

The DART Line of Sight system is similar to the two aspect signals used on SEPTA's Routes 101 and 102 suburban trolleys, although in that case the signals partly work as a more formal two aspect ABS system. DART Line of Sight allows higher speeds on stretches of track located on median rights of way or city streets governed by traffic signals.  It is worth noting that at least at the time of writing DART trains are scheduled such that only one LRV is expected to be in any LoS section at a time. For example a Red Line train departing Westmoreland is scheduled to enter ABS territory in 11 minutes and the maximum headway is 15 minutes. 

DART's Line of Sight system is a safe and innovative way to achieve cost reductions and enable Light Rail style in street or street adjacent operation with traffic and other non-interlocked signaling. Thanks to the straight jacket of PTC, non-FRA regulated light rail systems are the only place that are able to employ outside the box signaling and safety solutions.

SEPTA to Retire Rt 100 Stop Request Signals?

 A unique operating practice on one of the last true Interurban lines may be on the chopping block because as of December 8th, the passenger operated stop request signals are being taken out of service with cars now required to approach every station prepared to stop.  This may simply be a temporary measure due to COVID related ridership declines, but we will have to wait until the crisis ends to see. 

The system works as follows.  Passengers on the platform are prompted to press this button to stop train.

This illuminates a single unit Safetran CRS-20 signal located at the end of the platform with either a white or lunar light.  Trains scheduled to make a station stop will look for this light and will make a station stop if it is lit.

The really clever part of the system is how the light is canceled.  Instead of using the track circuit or some unreliable sensor, a short section of third rail is provided under the platform.  Normally isolated from the traction current, when a train passes through the station the opposite third rail shoe will touch the isolated rail and energize it, tripping a relay and extinguishing the stop request lamp.

With low ridership due to COVID, trains could have been running far ahead of schedule and SEPTA might simply be looking for a way to slow them down.  However, it is more likely that the system was deemed to have outlived its usefulness and presents a significant maintenance item in an age of budget cuts.  The system probably only saved a few minutes over the course of a trip and may have confused new or infrequent riders.  Also, with smartphones giving arrival time info, trains that ran ahead of schedule could have been angering riders when trains arrived before the time indicated on their phones.

Regardless of the reason, its yet another instance of service being degraded from what was achievable during the "analogue era" of yesteryear. 

DART - One System, Two Methods

Dallas Area Rapid Transit is one of the new generation of North American light rail systems, as large in scope as many heavy or commuter rail networks, but built to a much lower price point.  DART was built in two waves, the initial Blue and Red lines built between 1996 and 2002 and then the Orange and Green lines built roughly between 2010 and 2012.  Despite being part of a unified transportation system, DART uses two completely different signaling methods.

 Signaling on the Red and Blue lines consists of pretty standard ABS CTC with wayside signaling.  Signals consists of single direction stub masts placed back to back.  An ATS capability is provided via some sort of IIATS or Westcab transponder to enforce signals displaying Stop, however track speeds are not enforced.

Interlocking signals use a NYC Subway style system with the upper head indicating block state and the lower head route.  Thus G/Y is diverging clear and Y/G is approach straight.  Also note the use of traditional track circuits with impedance bonds.

Of course for the second phase Orange and Green lines, DART decided to switch gears and adopt a cab signal system without fixed wayside signals.  Cab signals are of the jointless audio frequency type and signals are only provided at interlockings with the ability to display Stop (R), Restricting (R/Y) and lighted directional arrows for everything else.

These directional signals were also used in the Phase 1 street running portion downtown, so it was natural to reuse the system in cab signal territory to reduce the need for re-training.

Unfortunately my photo of the cab signal display did not turn out, but there is not a lot of complexity.  The operator sees the vehicle speed in red LED and a target speed in orange LED.  The speed changes as soon as a new cab signal code is received with an ATO style brake application being instantly applied, as opposed to a penalty application after a grace period. This system enforced both track and block speeds with speed control in 5 or 10 mph increments between 10 and 60mph.

It was interesting to see these two generations of systems running side by side with Orange line trains in particular starting under one system and finishing under the other.  It was also interesting to see how much train operation was being impacted by the speed enforcement with operators having to brake about 5mph past the speed target and then re-accelerate.  This created a very jerky form of operating where as the lines without speed enforcement saw much smoother operation.

Although many light rail systems are adopting or converting to heavy handed forms of train control, there are still many systems built since 1990 that have retained lower cost, human-centric signaling systems that will likely be the last such examples as heavy and commuter rail lines become increasingly "supervised".

EDIT: DART actually has a THIRD method of operation that I discuss in a followup post.

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 ;-)