Signal Series – ABS, Part 2

ABS Signals, continued – now with route indications

So in the last post, I covered the basics of one-headed ABS signals – what the aspects and indications on them mean. To review:

ABS diagramDiagram of ABS signals

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)

Number of aspects = the route you are taking

“But wait,” you might say, “What do you mean by ‘primary route’?”  Or maybe you didn’t say that, but we’ll pretend you did.

One of the neat things about ABS signals on the MAX alignment is that the number of aspects of it that are lit tell you what route you are going on.  One aspect lit (as in the signals shown in the last post) = primary route.

So for something other than the primary route…

Train entering Elmonica yardSignal W1044, red over yellow aspect – Secondary route into railyard at Elmonica

Two aspects lit, as seen on this two-headed signal = secondary route (the top head is red, the bottom head which is separate from the top is yellow).  Here, at Elmonica/170th platform looking east, the secondary route diverges a train into the yard for the night.

In other parts of the alignment, the secondary route can diverge a train from the Steel Bridge towards the Expo Center, into the Red Line terminus at Beaverton Transit Center, the airport alignment from Gateway etc.

16G to IRQSignal 16G showing a diverging route of a red over a lunar

This picture was taken onboard a Yellow Line train coming off the Steel Bridge and heading towards the Interstate/Rose Quarter platform – note how the signal number separates the two signal heads. We’re not in ABS territory here, but this signal tells us that the switches are set for heading north towards the Expo Center (the secondary route) instead of heading east towards Gresham (which would display just a single lunar aspect for the primary route).

Old Signal 76Old picture of Signal 76, eastbound Red Line at Gateway

The above picture is old (and low quality, I used a camera phone) – taken before the Green Line to Clackamas alignment was tied into Gateway. At the time this picture was taken, only two routes were possible from the eastbound main track at Gateway – continuing onto Burnside and Gresham (primary route) or diverging to the Airport alignment (secondary route). Now there are four routes possible from this track so signal 76 looks different and is pictured below in this post. Anyway, this is a picture of the signal aspects that an airport-bound train got: a red over a green. This indicates that they are clear for two ABS blocks on the secondary route. It’s also possible for this signal to display a red over yellow, which would indicate to the airport-bound train that they were clear for only one ABS block on the secondary route. An airport train will still get a red over a green (or yellow), but it looks a little different on the new signal 76.

From Sunset TC westbound towards Beaverton Transit Center, there are three signal blocks where a Red Line train can select a route to diverge into the pocket track in Beaverton, which is the secondary route.  This is a unique setup on the alignment, and here is how the signals to do that will look, starting from Sunset:

Green over greenSignal W556, Green over green, Sunset Transit Center westbound

W556 is the only signal on the alignment that can display a green over green aspect.  The indication of this is “advanced advanced secondary route” – meaning that not in the ABS block between this signal and the next, and not in the block after that, but the block after THAT diverges to the secondary route.  Basically the top aspect tells you how much further on the primary route you are going to go before you diverge; and the bottom aspect tells you that you are going on a secondary route.

Yellow over greenSignal W616, Yellow over green

This is the signal at the end of the block that started with the green over a green at Sunset.  This is a yellow over a green, indicating “advanced secondary route” – meaning that not in the ABS block between this signal and the next, but in the block after that the train will diverge to the secondary route.  So you will be continuing one more ABS block before you diverge.

Red over yellowSignal W716, Red over yellow

W716 is the signal at the end of the block that began with W616. And similar to what you’ve already seen, this red over yellow aspect on signal W716 indicates that in this ABS block, before the train reaches another ABS signal, it will diverge to the secondary route.  So you will not be continuing on the primary route for any more ABS blocks (that’s why the top aspect is red) – look for switches that will change your route before you see another ABS signal.

So if one aspect = primary route, two aspects = secondary route..  then if three aspects are lit?  You guessed it – the tertiary route!

Signal 76, tertiary to ClackamasTertiary route (red over red over green) on signal 76, Gateway

And this is what signal 76 looks like nowadays – all aspects are on the same head. So it’s not my favorite example of showing three aspects (elsewhere in the system signals capable of displaying more than one aspect have them all on separate heads which is easier to understand), but this is a train eastbound at Gateway that is diverging onto the tertiary route, which is the Green Line extension to Clackamas. This indication is “Clear for 2 ABS blocks on the tertiary route” – notice how you are not continuing any further on the primary or secondary routes (both of those aspects are red), but you will be clear to continue for 2 ABS blocks on the tertiary route since the third aspect is green.

Tertiary, old signal 78Tertiary route (red over red over lunar) on signal 78, Gateway

This is an old picture (this particular signal at Gateway was also replaced for the opening of the Green Line) but it shows the 3 heads lit, indicating a move to the tertiary route, which at the time this picture was taken brought the train to the auxiliary track at Gateway.

Signal 78 as it now looksThis bad boy replaced that above signal. I don’t know enough Latin to say what the proper names for the 4th and 5th routes would be (quarternary, pentinary?), but Signal 78  is the only one in the system that will display a 5th diverging route.  Briefly this signal was designed like the new signal 76 (both pictured here as they were working on them), but they changed it to this design – I believe there had been stability issues and concerns about wind knocking it down with all the aspects on one head.

When more than one aspect on a signal is lit, the more restrictive color is ALWAYS above the less restrictive color (the only exception is Sunset’s green over green) – reds will always be over yellows, greens, or lunars, and on signals indicating advanced diverging route, yellow will always be over green.


7 responses to “Signal Series – ABS, Part 2

  1. Pingback: Tweets that mention Signal Series – ABS, Part 2 « MAX FAQs --

  2. nope not gonna do it

    Quartenary and quinary are the answers you seek. However, this signal in particular is what pushed the elimination of “primary route” “secondary route” etc. We now call them the same thing the signal techs call them: “A Route” “B Route” “C Route” etc. This is also why all five of those heads are labelled the way they are.

    • Do you happen to know where the “A Route,” “B Route,” “C Route,” “D Route,” and “E Routes” go from this signal?


      • Were you asking me or “not gonna do it”? I don’t think he’s been back at my blog in a while, not since he went through and corrected a few of my mistakes and filled in some of the gaps!

        Anyway, routes possible from signal 78:
        A: One aspect (lunar): Eastbound main (Blue line towards Gresham)
        B: Two aspects (red over yellow OR red over green, depending if you’re clear for one or two ABS blocks on the diverging route. Red over green is the most typical): Airport extension (Red line)
        C: Three aspects (red over red over yellow OR red over red over green, again depending if you’re clear for one or two ABS blocks): Clackamas extension mainline (Green line to Clackamas)
        D: Four aspects: (red over red over red over yellow OR red over red over red over green): Main Street pocket track – so diverging onto the Clackamas extension but ending in the pocket track before Main Street instead of going to the platform.
        E: Five aspects! (and I’m starting to feel like the Count from Sesame Street): Red over red over red over red over lunar – Auxiliary track.

        And from signal 76, the A-D routes are the same, you just can’t go from there to the auxiliary track so there’s no need for a fifth aspect on that signal.

  3. Thank you very much for your response!

    By the way, I’ve got a ton of questions that I was hoping you could answer but is there an easier way to contact you (e.g. email)?


  4. I noticed on the westernmost pull out track from Elmo (the one train 20 will pull out on to go to Hillsboro at the crack of dawn), there appears to be 3 aspects on the signal as the track veers into the westbound mainline. Why are there 3? Since the Elmonica platform is like only 200 feet away or so, shouldn’t there be 2?

    • Good eye! But 2 of Elmo’s yard signals are a little bit different from mainline ABS signals. The one you’re talking about is W1030, and you’re correct, it can display 3 aspects, but instead of red-yellow-green, it’s red-lunar-yellow. This is done to allow a couple up move in the westbound mainline. Assume there’s a single car in the westbound track and you want to take a car from the yard and couple them to have a two-car consist on the mainline instead of the single car. With most ABS signals, you can’t get a permissive aspect to move into a block if there’s a train already there, so you wouldn’t get a yellow to do that move. So instead, you get a lunar (this does require a different route code than a normal westbound move), which tells you that the tracks may not be clear, and they’re not – there’s a car in the platform that you’re going to couple to.

      Next time you go through there westbound, take a look at W1020 as you go by, it’s the yard signal that’s near the building. Two heads, the top with 3 aspects, the bottom with one. The top can display red-lunar-yellow and the bottom can display lunar. The top aspects serve the same purpose as they do on W1030. The red over lunar is for a train to leave the yard into the eastbound platform at Elmonica/170th – the lunar allows a couple up move to be done in that platform if necessary, otherwise a train will just pull all the way in, the operator will swap cabs, and continue east.

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