Tag Archives: abs signals

Conga line

Westbound trains were delayed Friday due to a switch issue by Beaverton Transit Center. There are three power switches to get into or out of the pocket track from the east, and the one farthest to the left in that picture was not throwing properly, so rail supervisors were on scene to manually throw the switch and direct trains safely through the area. I was off work and downtown when all of this was going on and from what I could see the operators were doing everything they could – getting on the PA to announce the reason for the delay and apologize for the inconvenience. Surprisingly, given how backed up everything was, no official service alert was released. Of course, people weren’t happy about the delay or being stopped for a while only to proceed up to the next platform and then stop again.

Not a great time to be operating, but a good topic for blogging…

Things were very backed up – this conga line of trains at every platform on Morrison is the result of that issue way out by BTC. If you look closely, you can see there is a Type 4 up at Galleria, then another train at Pioneer, then this train next to me at the Mall/5th platform, and another train behind it at 3rd/Morrison.

A common complaint I was hearing was that passengers didn’t understand why the trains were stopped where they were – can’t they keep moving, even if slowly? There are a couple of reasons why trains were holding where they were. One: stopping away from platforms is something to avoid whenever possible. Passengers can get a little agitated and uncomfortable being on a train that isn’t moving, and it’s dangerous for them to pull the emergency door release to leave the train away from a platform – first because that can likely put them in the path of a train coming in the other direction or vehicle traffic (depending on your location), and second because even the low-floor train cars have a drop to the ground if you’re not at a platform. So it’s preferable for stopped trains to hold at platforms with their doors open or on release which allows people to leave the train safely.

Two: west of Goose Hollow is ABS territory. To review:

ABS diagramDiagram of ABS signals

The direction of travel is from left to right. On the top part of the image, a green signal indicates that there are two open blocks (that is, the space between the signal in front of you and the signal after that one, AND the space between that signal and the one after it both are clear of trains). In the middle part of the image, the yellow signal indicates that there is one open block between  you and the train in front of you. The bottom part with a red signal indicates that the train in front of you is in that block. If the block in front of you is occupied, you CANNOT proceed into it. The block system and associated ATS magnets work to keep the trains spaced at a safe distance and prevent collisions.

So even though there appears to be more than adequate space for all of these trains to have rolled through downtown and waited behind each other on the alignment just east of Beaverton TC to proceed through, multiple trains cannot safely occupy the same ABS block. Additionally, since it’s safest to have the trains holding at platforms whenever possible, it’s better to have the trains stacked up here than at each ABS signal along the west side where there is no safe way for people to exit the train if they’re not at a platform.

Conga line of trains proceeding through downtown, monitored by supervisors

Repeater signals

Another post about signals… this time the rail kind. I thought about this while writing the last post, because this is sort of like a literal signal boost.

There are two signals on the Banfield between Lloyd Center and Hollywood TC that function differently from the rest of the signals on the alignment. These signals (34R and 36R) are repeater signals. They “repeat”, or display the same aspects, as ABS signals 34 (eastbound) and 36 (westbound) respectively, but are positioned slightly ahead of the signals they repeat because those signals are around a curve.

34 R (eastbound), which is repeating the aspect displayed on…

…Signal 34

Signal 36R does the same thing for signal 36, which is seen going westbound. I don’t have a picture of signal 36, but here’s its repeater signal:

Signal 36R (westbound). Signal 36 is located around the curve ahead, back-to-back with signal 34.

The speed limit through here is 45 mph, so due to the limited visibility with signals 34 and 36 being on a curve, it would be difficult to stop a train in time if those signals were red. The repeaters give advanced notice of what aspect those two signals are displaying so operators can act accordingly and stop if necessary.

Notice how there are no ATS magnets near the repeater signals, but you can see the ATS magnet (it looks like a small box between the rails) in the picture for signal 34. Going through a red on 34R or 36R won’t automatically bring your train to a stop, however, you still treat like all other red signals and stop your train prior to the repeater if it’s red. And if you run a red on a repeater signal and then trip the signal after it, I believe that counts as two rule violations for going through two red signals (which I’ve never done..).

Train numbers, route codes, and more with signals

Question: How does a train know where to go?

This question comes up a lot, and although I’ve answered it in comments or emails or Twitter, I’ve never given it its own post. But a lot of people have asked, for example, if a train is eastbound at Gateway, what do you do to it to send it to Gresham vs the airport vs Clackamas? Sure you call the signal but how do you get the right aspect(s) to come up for where you want to go? It’s not like the trains have a steering wheel.

(Actually it’s kind of fun to let kids see the cab of a train at the end of the line and ask them where the steering wheel is. It stumps their parents too!)

It’s a trick question.  Here’s the “steering wheel” of a MAX train:

Route code (and train number, which is blurred out, you don’t need to know what train number this was, but in following safety procedures, I assure you the train was stopped at the end of the line – not only was it not moving it wasn’t even keyed in), Type 2 thumbwheels

In the cab of each train is a place to set the train number (under normal operating conditions, this won’t change over the course of the day) and also the route code. The train number is the train’s identifier, and it matches the number visible in the window box – for example, the train in the old header picture of this blog was train 40; the train in the old background image was 71. If Control wants you, they’ll call your train number over the radio. If you need something, you begin a radio call to Control by stating your train number.

You can tell what yard a train is from (though not necessarily what yard the operator is from due to reliefs) and what color its route is from the train number. Trains 1-15 are Blue originating out of Ruby, 20-38 are Blue out of Elmonica, 40-53 are Red out of Elmonica, 60-74 are Yellow/Green out of Ruby, and the Mall Shuttle had been train 89 out of Ruby. Trains not regularly scheduled, such as those used for testing or burn-in get numbers in the 90s. There are some exceptions to this breakdown, like train 10 is Blue most of the day but becomes Red at night, 43 begins its day going from Elmo to PDX to Hatfield before becoming a regular Red Line, but this is all pretty much just trivia for passengers anyway, it’s not like I’m going to quiz you on this later.

The route code is what tells the train where to go from its current location. Every possible destination on the alignment that can be reached via power switches has a route code assigned to it – not just the ends of each line, but also the yards, sidings, pocket tracks, etc.

Sign at Galleria with 11th Ave route code

In the first picture in this post, a route code of 50 will get a train to either track 1 or 3 in the Jackson turnaround by PSU, whichever is open. Every time an operator places a train-to-wayside call over a call loop, the switches will be set to move the train toward the destination set as the route code, and the corresponding signals will be displayed. Operators are responsible for ensuring the route code is correct for where the train is supposed to go. For Blue and Red line trains, this is pretty easy – the cab that leads going east will be set for Gresham or PDX, and the cab that leads west will be set for Hillsboro or BTC so it does not need to be adjusted frequently (well, it’s easy as long as Red line operators don’t forget to change the route code from the BTC pocket track on the last trip and end up in there when they need to keep going west…).

Yellow/Green line trains are a little trickier. For trains leaving Ruby to service those lines, depending on which run it is the route code will be set for Expo, the Jackson turnaround, or the Gateway auxiliary track (where the operator will swap cabs and take the train to Clackamas). Then to change color at Jackson, the operator will leave Clackamas (for example) with the route code for the Jackson turnaround, and then once there will set the route code for Expo. When leaving Expo in the other cab, they’ll set the route code for Jackson, and then once in the Jackson turnaround, they’ll change the route code for Clackamas. Potential errors can happen if an operator forgets to change the route code from 50 when leaving Jackson (if that happens, the train will head back south to PSU from Union Station instead of crossing the Steel Bridge) or forgetting to set the route code for Jackson from the end of the line (so for example, heading toward Clackamas from Interstate Rose Quarter instead of over the Steel Bridge).

Signal aspect review

Signals will reflect what route code is in your thumbwheel. First, here’s a quick overview  of signal aspects (for more information, I’ve written a lot about signals already)

A red aspect – STOP

A yellow aspect – clear for one ABS block (that is, the distance to the next ABS signal) on the primary route

A green aspect – clear for two ABS blocks on the primary route

A lunar aspect – proceed with caution, tracks may not be clear (your switches are set but no indication of train occupancy ahead)

The number of aspects that are lit indicates which route you’ll be going on (one aspect = primary route, or “A” route. Two aspects = secondary route or “B” route. Three aspects = tertiary “C” route, etc). As an operator, when you’re looking at a signal that can display more than one route, you need to know which of those routes corresponds with the route code you have in your thumbwheel.

Back when I was first learning the signals, one of the most confusing parts for me was confounding signal aspects with switch positions, in part because yellow over green signals are referred to as “advanced diverging” and red over yellow are referred to as “diverging” – so that means when you see one of those signals, you can expect switches to be set diverging, right? Well, not necessarily…

For example, at the ends of the lines (here into Cleveland Ave from Gresham TC) a single yellow aspect will actually put you over diverging switches into Cleveland, but a red over yellow is a straight shot in. A signal with two aspects means that you’re diverging from the primary route, but not necessarily diverging over switches – it could be that the primary route itself diverges over switches but the secondary route goes straight. I had been thinking about the ABS signals in terms of switches, not routes, and that was a stumbling block for me. A permissive signal indicates that your switches are set for whatever your route code is, but you have to know if that means they’re diverging or normal.

Same with this red over white vertical on W1760 at Hatfield – it’s a secondary route (2 aspects), but this train will be going straight in, not diverging over the switches. Sorry for the blurry picture but it’s the only one I have.. I either need to go out there and get a clearer one or get someone to do that for me.

It’s not where you are, it’s where you’re going

So keeping in mind that an ABS (or ABS-pre-empt combination) signal displays your route, here’s an example of what it looks like when you can call the same route from two different locations. Take a look at these signals:

Signal 76: Red over red over green
Clear for 2 ABS blocks to Clackamas TC

Signal 78: Red over red over yellow
Clear for 1 ABS block to Clackamas TC

Both trains that called these are facing east at Gateway – the one looking at signal 76 is in the eastbound main; the one looking at signal 78 is in the pocket track. Both have a route code set for Clackamas TC. And from both tracks, that’s the “C” route / 3rd route / tertiary route, which is why both signals are showing 3 aspects. These aspects are almost functionally identical (the yellow on 78 just means that this train’s leader is only one ABS block ahead of them, otherwise that would’ve been a green) even though the train observing signal 78 has two more sets of switches to diverge over to get to the eastbound main to get to Clackamas.

Gateway from above, click for larger

The platforms are in the bottom of the picture – from left to right, that’s the westbound mainline, pocket track, and eastbound mainline. Notice that to get over to the eastbound main alignment (which, out of range of the top of the picture, diverges off to Clackamas) a train in the pocket track has to pass over the switches that could otherwise bring it to the auxiliary track, and then over another set of switches to join the eastbound main. Yet its signal aspect at Gateway to get to Clackamas is identical to what a train in the eastbound mainline would get, even though the train in the eastbound mainline doesn’t have to worry about those switches.

Where a train is starting from doesn’t matter – where it’s heading is what will be displayed on the signal.

Lunar on signal 78, eastbound from Gateway pocket track

Lunar on signal 76, eastbound main at Gateway

Similarly, a train with a route code for Cleveland (or the Ruby Yard) going east from the pocket track will get a single lunar aspect on signal 78, just like how a Blue Line train heading east at Gateway will have a lunar on signal 76, even though a train starting from the pocket track has to diverge over switches to get there. The signal indicates that the switches are set for the route code in  your thumbwheel, but you have to know if that means the switches are set normal or diverging (because you do NOT take a train at a high speed over these diverging switches!)

Here’s another example, eastbound at Beaverton Transit Center.

Signal W760 is for a train in the pocket track (which is typically a Red Line), and W754 is the signal for the eastbound main. A train heading east from the pocket track will have to diverge over switches to get into the eastbound main, yet the ABS signal will show a single aspect indicating the primary “A” route. It doesn’t matter where the train is at, it matters where it’s going – and for trains in either track here, the only place to go is the eastbound main (primary route), therefore both signals have a single head that can only display a single aspect. There is no choice of route from either track, even though you will be diverging into the main eastbound track if you are leaving the pocket track.

W556 at Sunset, for a Red Line train heading to the BTC pocket track

On the other hand, if you’re headed west into BTC, you do have a choice of two routes (along the westbound mainline or into the pocket track), which is why signal W556 at Sunset and the intermediate signals leading into BTC (W616 and W716) can all display one or two aspects for a primary or secondary route. The signals will indicate that the switches are set for whichever of those route codes you have in your thumbwheel.

You know, I don’t know how to end posts. I feel like I should assign a 2-page essay on the importance of ensuring you have the right route code in your thumbwheel and how that relates to ABS signal aspects. Show your work.

Civic Drive

Civic Drive Iris

Last month was the opening of the Civic Drive platform. Located in Gresham between Gresham City Hall and Ruby Jct/E 197th, this is now the 85th platform in the system, though construction had originally begun about 15 years ago. For years, Civic Drive was closed off and treated like a bypassed platform by operators  with a speed limit of 20mph past the platform.

Not to be confused with the no-longer-named-that Civic Stadium

Old signal 138, Gresham City Hall westbound

When Civic Drive was still a closed platform, this signal at Gresham City Hall facing west was used by trains to either continue on the westbound main (getting a yellow or green aspect) or to select for the Ruby yard (a yellow over green aspect). Signal 134, the intermediate signal in the cut westbound between Civic Drive and Ruby Junction, would display a corresponding yellow or red over yellow aspect depending on what route the train selected.

Current signal 138

But now there’s a new platform in between City Hall and Ruby, and you can’t be clear to proceed for 2 ABS blocks when there is a platform in the next block. As previously mentioned, the ABS signals prior to a platform will not display a green aspect. So now signal 138 will display just a single red or  yellow aspect.

Continuing west..

Civic Drive, westbound

A few points of interest here – you can see the call loop for our train (between the arms of the windshield wiper), and a sign to call signal 134, which is located way out in the cut. It’s red in the above picture, which might be easier to see in the larger version. Also visible from here are the ATS magnets as this part of the alignment is speed tripped for eastbound trains.

Signal 136A

136A is a new signal that was added for eastbound trains at Civic Drive. It can display two possible aspects since Gresham City Hall is the next ABS block.

How futuristic

Both sides of Civic Drive feature blue lighting built in along the ends and edge of the platforms.

And continuing further west, this is a closer view of signal 134, which is the same as it has been. It’s yellow for us since this train is headed to Hillsboro, not diverging into the Ruby yard.


Question: What do you mean by “circuit”, anyway?

I’ve mentioned rail circuits in a number of posts but I’ve never really explained them. So that’s what this post is for.

Don’t step on the rails

The rails are actually electric circuits – there is an electric current passing through the rails on all parts of the alignment. The voltage is low (15-25 volts) so it’s not harmful, but it’s just one of those “best practices” to not step directly on a rail. I’ve never heard of a person getting shocked by them, though there have been problems in the past of service dogs (see attachments 3 & 4 for TriMet specific examples) being shocked when stepping on the rails, particularly in wet conditions. As far as I know, that problem has been resolved and hasn’t happened in years.

Insulated Joints

The boundary between two circuits in the track is called the insulated joint. You won’t see these from the train, but you can feel/hear them as the train passes over them.

Insulated joint.  I forget where specifically this was taken.

I don’t have any video that I’ve taken myself which provide good audible examples of what it sounds like when a train is going over the insulated joints. Luckily, other Youtube videos provide. I’m shamelessly borrowing these examples – I did not shoot the video in either and take no credit for them.

  • Train at Old Town/Chinatown, video taken from outside the train (link should take you to the right spot at the video, but if not, move the seeker to about 7:11).
  • Train at Merlo Road, video taken from inside the train (at about 1:48)

What you’re listening for is that short sort of skipping sound made as the wheels pass over the joint. On the external example, you can hear it as each of the three wheel trucks on both cars passes over the joints (sounds like 6 sets of 4 clicks); inside the train only one truck is clearly audible.

Insulated joints in CBD – this might be Lloyd Center westbound, I don’t remember

The basic “how it works” principle is that the wheel axles of a train shunt the circuit in the rails, thus detecting the presence of a train in that particular circuit. As the train moves along the alignment, it passes over the insulated joints from one circuit to the next, which indicates what sections of the track are occupied by a train.

So speaking of track occupancy

As you might have guessed, insulated joints and track circuits are directly related to ABS signals.

Bringing up this picture again:

Train movement in the diagram is from left to right. To review, if you’re in ABS territory and you have a green, that means you’re clear for two ABS blocks, or the distance between the next two ABS signals. A yellow tells you that the block ahead of you is open, but there’s a train in the block in front of that. And if you get up to the next ABS signal and it’s red, that means the train in the block in front of you hasn’t left yet.

So how do the signals “know” that there’s a train there?

If a shunt is detected in the rail – meaning that something is going across both rails closing the circuit (namely the wheel axles of the train), the signal displays an aspect that indicates that the circuit is occupied – a red if it’s the circuit immediately after that signal, or a yellow if it’s not the circuit immediately after the signal but the circuit after the next signal.

So when you have a red ABS signal, that means a train is shunting the circuit after that signal and that section of track is occupied. Once that train ahead of you passes the next ABS signal, which will have an insulated joint associated with it, it leaves that circuit and the signal that you’re waiting at will display a permissive aspect. This indicates that the block in front of you is now open.

A good place to see how this works are the ABS signals at platforms. If you’re sitting near the front of the train on the left side, you can watch the signal change from yellow or green to red as you hear the wheels pass over the joint, which indicates that that circuit is now occupied by a train. If you’re sitting further back, the signal will already be red as you pass it. From outside the train, it looks like this:

Eastbound at Beaverton Transit Center

You can’t see it in the above picture, but there is a train immediately to my right that called signal W754 and got a green. Notice the insulated joint right about at the corner of the platform. Once the wheels pass over the insulated joint, shunting the circuit associated with that signal…

The signal becomes red, because now there is a train occupying the circuit. To conserve power, this particular signal will go dark once the circuit at the platform is no longer shunted, but if another train comes into the platform before this train passes the next ABS signal, W754 will display a red aspect again.

A blurry picture, but it was taken from the trailing parlor cab of a Type 4 – so the three wheel trucks of the leading car have already shunted the circuit after the signal, making it appear red for the rest of the train.