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:
Diagram 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…
Signal 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.
Signal 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 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:
Signal 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.
Signal 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.
Signal 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!
Tertiary 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 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.
This 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.