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.
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:
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.
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.
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.
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.