Tag Archives: abs signals

Bait and


I’ve gotten a few questions about some things people have spotted on Interstate – namely “signals” that don’t match anything I’ve described in my signal series. That’s because those aren’t signals in the same sense of the word that the ABS or pre-empt or combination signals are. Those are called summary switch indicators or advanced switch indicators, and then I figured a post or two on switches first would be helpful to explain what those are.

So I will get to those soon, but first, here is your introduction to switches. Two main things to remember:

1. A switch can be set to normal or diverging – normal to continue straight; diverging to move the train to (or from) another track.

2. The part of the switch that moves and that generally matters the most to operators are called the switch points. When a train goes over a switch and the points are facing the train (which gives you the choice of diverging or not), that’s called a facing move. When a train goes over a switch and the points are facing away from the train, that’s called a trailing move.

Types of rail, types of switches


T-rail makes up the majority of the alignment. Switches in t-rail have indicators associated with them (the appearance of which will vary depending on the type of switch it is) that will display green if the switch is set for a normal route and yellow if it is set to diverge.

Picture borrowed from another operator’s blog – I think this is westbound on Burnside at 172nd

These are manual switches on Burnside set to normal. Note the green targets on top of the switch machines – this shows that the switches are set normal, which you can verify by observing the points of the switch ahead. Throwing the switch to diverging rotates those targets to display yellow.

This is a trailing move for us – the points of the switch are facing away from the train and there’s no way we can get on the diverging track from this direction (we’d have to go past the switch points, get out, walk to the other cab, and run eastbound in the westbound track to diverge) Also visible is a speed limit sign, and a decision point marker, as well as the C & P signs, but you already know what those are.

Elmonica 170th platform

Remember this picture that I used a while back to show the diverging route on the ABS signal at the Elmonica platform? Now look down the track a short distance, and you can see the yellow switch indicator lights showing that the switches have been thrown to diverging. This train is going to diverge off of the mainline into the Elmo yard.

Girder rail

Girder rail is the pavement embedded rail that is found downtown, along Holladay, and along Washington in Hillsboro. This type of rail is shallower than t-rail and is prone to getting filled with debris (like in the fall when city maintenance people blow dead leaves into the right of way…) and so it is only used in lower-speed areas.

Westbound through Rose Quarter interlocking

In this picture, we’ve just left the Rose Quarter platform (I think this was a Blue Line train) and we’re moving over one girder rail switch as a trailing move, and there’s another up ahead which is a facing move. This is how trains can switch to the Interstate alignment as well as the special events track in the Rose Quarter platform. Notice that girder rail switches have no green or yellow indicators to show how they are set.

Power Switches

mainline power switchT-rail power switch on the mainline

Power switches are all of the switches that can be thrown from the cab of a train with the Vetag. For a refresher on how it works, revisit my post on call loops – a train stops with the transponder over the call loop which allows the operator to remotely throw the switch. Power switches can also be operated manually if necessary, and so for safety reasons all t-rail power switches on the mainline are padlocked as you can see in the above picture.

Manual Switches

Throwing a manual switch (t-rail) – both colors of the target visible here

Manual switches (in both t-rail and girder rail) cannot be thrown remotely via the Vetag and must be thrown by hand. So switches that are frequently used on the mainline are more likely to be power switches, because those can be thrown much faster than a manual switch.

11th ave switchesGirder rail switches, 11th Ave terminus

In girder rail, power switches and manual switches look the same – the above picture shows two power switches and a manual switch which are used to get a train into the 11th Avenue terminus.

Do not, under any circumstances, try to throw a switch, touch a switch, attempt to remove the padlocks, etc. Aside from that being a stupid thing to do because of the risk of getting hit by a train, there’s probably some sort of criminal offense involved in tampering with anything that could potentially derail a train.

Does it get more complicated than this?  Of course!  More in the next post.

Old OldTown/Chinatown signal

I forgot I had this picture, otherwise I would’ve included it as a point of sort of historical interest in my ABS/Pre-empt Combination Signal post:

Old view eastbound at Oldtown/ChinatownCab view, eastbound at Old Town/Chinatown several years ago

This is an old picture, taken back before the Portland Transit Mall was integrated to have the the Yellow and Green Line trains running on 5th and 6th.  That pre-empt signal isn’t there anymore – the way this used to work was that an eastbound train at Old Town/Chinatown would call their pre-empt and then begin to proceed up the Steel Bridge on a proper signal.  Signal 10 (which I have no picture of) was located on the bridge prior to the span, displayed a red or a lunar, and was associated with an ATS magnet – so if, for example, the bridge was going to be lifted, signal 10 would be red and the magnet would be active.

But then the Portland Transit Mall happened, and that meant tracks approaching the bridge from a different angle where the Yellow and Green trains go across the river from Union Station and now the added possibility of a Yellow or Green train making a conflicting move to a train at Old Town/Chinatown heading east.  So now Signal 10 is a combination signal located where this pre-empt was, and Old Town/Chinatown has an ATS magnet. I forget specifically when this change happened – in 2008 I think.

New signal 10The new Signal 10 – here the train operator has called it, but doesn’t have pre-emption of the intersection yet.

So there’s a little bit of TriMet rail history for you.

I lied – More signals!

Okay, I forgot two.

Dwarf Signals

Ruby Jct/E 197th, looking eastDwarf signal in lower left corner

I love this picture because there’s so much going on in it.  Ruby Jct/E 197th looking east, zoomed in (I took the picture from the westbound platform) so the quality is a little grainy and the distance is flattened out – objects in the picture are much farther away than they appear!

I forgot the dwarf signals because under normal operating conditions, you don’t really see them because they don’t face you. Dwarf signals for MAX are only used when running reverse – notice how in the above picture which is facing east, the dwarf signal is on the westbound track, so you’re only going to see it if you’re going east in the westbound.

Anyway, the purpose of dwarf signals are to protect power switches on the mainline when you’re running reverse in ABS territory. They won’t display any aspect other than red, though some will go dark if there’s no train in the circuit. They’ll be associated with ATS magnets and switches.  When running reverse without signal protection, you must stop at all switches to make sure they are properly set since you’ll be coming at them from the wrong direction.

Dwarf signal at BTC“Dwarf” not always short

Here’s dwarf signal W768 and two standard ABS signals at Beaverton Transit Center looking east.  They’re all the same height, but the dwarf is the only one that can only display a red aspect.  In this picture it’s dark because there’s no train in the circuit.

Same signal, now with a train in the circuit (in the westbound platform)

That particular signal protects the switches that Red Line trains take into the center pocket track at Beaverton Transit Center – which are located pretty far around that curve, so dwarf signals aren’t always right on top of associated switches.

The C Signal

For lack of a better name, anyway.


There’s only one of these that’s still in use, and it’s at Skidmore Fountain westbound (there is also one at 11th & Yamhill, but it is not active). The intersection after this platform is SW Ash, but you can’t see it from here, so when an operator selects at Skidmore westbound, the “C” signal illuminates to let them know that the call went through and they can leave the platform.  When they get to Ash, they should have their pre-empt.

Next up – not sure yet, but it won’t be signals!

Signal Series – ABS/Pre-empt Combination Signals

Okay, back to signals.  So there are your ABS signals, which indicate both track occupancy and switch position (by showing which route you are going on)

And then there are the pre-empt signals, which permit trains to go through intersections where the trains and cars run in mixed traffic.

But since pre-empts on their own don’t tell you anything about how switches are set or train occupancy, when in pre-empt territory you need…

ABS/Pre-empt combination signals

Which I admit I have a tendency to short to “combination signals” and then even from that to “combo signals” because that’s altogether kind of a mouthful.

Signal W2, a combination signal located at the 11th Ave Terminus

Combination signals can display both the red aspect of an ABS signal, indicating STOP as well as the yellow horizontal and white vertical aspects of a pre-empt signal.  They are used in pre-empt territory for several reasons:

1. To switch a train to a secondary or tertiary route

2. To indicate occupancy of someone else in the circuit

3. To prevent a train from moving into a conflicting move

4. To keep trains from going on the Steel Bridge if/when a bridge lift is in progress

Diverging to another route

Remember how the number of aspects lit on an ABS signal tells you which route you’re going on? (one aspect = primary route; two aspects = secondary route; 3 aspects = tertiary route, etc).  Well it’s the same with ABS/pre-empt combo signals.  I’ll keep using W2 as an example. If it helps, here is the 11th Ave terminus from above. W2 is located on the corner of 11th and Morrison and is used by trains heading west.

For Blue (westbound to Hillsboro) and Red (westbound to Beaverton Transit Center) trains under normal operating conditions, W2 will pretty much behave as a regular pre-empt signal once the operator places their call for W2 at Galleria.

Red on W2Red on W2

This indicates STOP and is what W2 looks like by default until an operator selects their route from the Galleria platform. Similar to a red on an ABS signal, reds on combination signals will be associated with ATS magnets that a train cannot move over.

Yellow horizontal W2Yellow Horizontal on W2

When an operator of a Blue or Red line train is at Galleria, they watch W2 (which is a block away) and wait for the red to become this yellow horizontal. That shows that their switches are set to continue straight on to Hillsboro/Beaverton (primary route, so one aspect), and by the time they get up to the intersection of SW 11th & Morrison, it (should!) turn to this:

White vertical on W2White vertical on W2

Which, as you already know, indicates “proceed with caution.” Because you get dumbass cyclists like that one biking against the light.  Good job, unknown cyclist – lucky for you that train was going straight and not going to hit you as you cycled across the diverging tracks!

11th ave switchesSwitches into 11th Ave Terminus

Here’s how the switches look to an operator – the train I was on when I took this photo was a Blue Line stopped at Morrison. This train would be continuing west instead of diverging into the terminus, and so the switches are set for the primary route, which is to head west towards Beaverton/Hillsboro. You can see the yellow horizontal on W2 in the top left corner of the picture, which indicates that the switches are set for the primary route but we can’t enter the intersection yet.

When Yellow Line trains used to turn around at 11th Ave, they’d get a different aspect after selecting their signal from Galleria:

Red over yellow horizontalRed over yellow horizontal on W2

The indication of this signal is “STOP – switches are set for something other than the primary route (more than one aspect), but you don’t have pre-emption to enter the intersection yet” – these aspects would display for trains diverging into the terminus after their switches were set and before the permissive white pre-empt aspect(s) came up.

So my picture of W2 showing a red over white diagonal over white vertical aspect indicates permission to proceed with caution on the tertiary route.  3 aspects  = tertiary route. The tertiary route from W2 is the easternmost diverging track into the terminus.

A secondary route on W2 would be the red aspect over just a white vertical, but I never got a picture of that – if all tracks at 11th Ave were empty, a Yellow Line train would first be put in the tertiary track, and the secondary track would be used if another Yellow Line train entered the terminus while the first was still there. That didn’t happen while I was standing there taking pictures that day.

Other combination signals that will show these same indications for primary, secondary, and tertiary routes can be found at end of the line signals W1760 immediately prior to the terminus at Hatfield in Hillsboro, and M164 which is the combo signal immediately prior to the Jackson turnaround for Yellow/Green Line trains at PSU.  There is also 18B into Rose Quarter from the east, which allows a train to continue on the normal westbound track (primary route), the special events track (secondary route), or the Vintage Trolley barn (tertiary route).

Secondary route, W1760Sorry for the blur but it’s the only picture that I have of an ABS/pre-empt combination signal displaying a secondary route – Secondary route on W1760 (under the car traffic light, it’s a red over a white vertical)

Circuit occupancy

On the other side of the 11th Ave terminus for eastbound trains is signal W6, another combo signal. An eastbound train coming up Yamhill can’t enter the terminus so W6 isn’t there for route selection, but a red on it will indicate that something else is in the circuit – either a train leaving the terminus, or a streetcar on 11th Avenue.

Red on W6 – because a train is leaving the terminus, so the ATS magnet associated with W6 will prevent an eastbound train from colliding with it

Permissive white vertical on W6 & eastbound train – you can see that the train that was pulling out of the terminus in the picture above this one is far enough ahead that it’s safe for this eastbound train to keep going.

Preventing a train from moving into another train’s conflicting move

There is a siding track that diverges off Holladay at 11th which used to be used by the Vintage Trolley and is occasionally used by MAX trains taken out of service (and yes, another combination signal – 20A – is used to make that diverging move).  Signal 20C at Lloyd Center westbound is associated with that siding track.

20C20C, Lloyd Center westbound

A train facing this direction has no option to choose a different route, but the combo signal will prevent a westbound train from moving forward if a train is going to go into or come out of the Doubletree Siding.

Steel Bridge Lift

All signals leading to the Steel Bridge (on the east side of the river that’s the Rose Quarter platform for Blue, Red, and Green trains and Interstate Rose Quarter for Yellow trains; and on the west side of the river that’s the Oldtown/Chinatown platform for Blue and Red trains, and the intersection of NE 3rd & Glisan for Yellow and Green trains) are combos. Whenever the bridge is lifted, it throws up reds on all of those surrounding signals.  As mentioned in the Automatic Train Stop post, although a yellow horizontal and a red both indicate STOP, a train still can physically move on a yellow horizontal, but it (by default) can’t move on a red.  So as soon as the bridge span is unlocked for a lift, all trains will be prevented from getting anywhere near it.

Red on M26Red on M26, the last mall signal before the Steel Bridge at 3rd & Glisan,  taken from trailing car of  a Yellow Line train

The interlocking of tracks around the Steel Bridge is extremely complex – on the west side, the Yellow and Green Lines cross the Steel Bridge from a different angle than the Red and Blue Lines, and then on the east side the Yellow Line turns north towards Expo and the other lines continue east.  Since all of those moves are done through switches in the rails, the combination signals will also display reds if another train is making a conflicting move (e.g. if a PSU-bound Yellow Line at Interstate Rose Quarter leaves the platform just before a westbound Red/Blue/Green line train tries to leave Rose Quarter), or if the switches aren’t set right for you – this is why sometimes you will be sitting on a Yellow or Green line train at 3rd & Glisan waiting to cross the bridge for a while (which means a Blue or Red left Oldtown/Chinatown and got onto the bridge before you got there), or similarly be sitting at Rose Quarter on a Blue, Red, or Green train waiting for a Yellow Line to get out of the way.

Reds on 16B and 16CReds on 16B (special events track at Rose Quarter) and 16C (main westbound track at Rose Quarter)

Both of those above ABS/pre-empt combination signals are capable of:

switching a train to another route (this is how trains can get from here over to the Expo Center from the Ruby Junction railyard – they can diverge from here)

preventing a train from moving if there is another train in the circuit

preventing a train from moving if the switches aren’t set right for them, and

stopping a train if the Steel Bridge is going to be lifted.

And that pretty much covers the last of the 3 major signal types used on the MAX light rail alignment.

Automatic Train Stop

A pause in the signal series, because it was getting too difficult to write about the last type without having explained ATS first.

ATS, or Automatic Train Stop, or “What keeps the trains from crashing into each other?”

Link to Wikipedia article, for those that like that sort of explanation

ATS in t-railATS magnet.  I don’t remember where I took this pic, but I think it’s Beaverton Transit Center, westbound platform

ATS in girder railATS in girder rail, Lloyd Center westbound platform

These little yellow rectangles are found all throughout the alignment, much to the delight and happiness of rail operators.  These are the ATS (automatic train stop) magnets, and given their name it’s pretty easy to figure out what they do. If a train goes over one while the magnet is active, the train automatically comes to a stop.

They are associated with every signal capable of displaying a red aspect, and will be active as long as that signal is red.  So, by default, a train physically cannot run a red light – attempting to do so will bring the train to an irretrievable stop.

ATS magnet and red signal aspect, Sunset TC westbound.

That magnet is currently active. Stopping the train and selecting for a permissive signal will turn the magnet off once that signal displays something other than a red aspect, which allows the operator to move the train forward again. If the operator had tried to keep going, her train would have been brought to a stop (and she’d have some explaining to do and paperwork to fill out!)  Again, if you scan the radio, that’s what’s called a “trip”, sometimes also referred to as “popping a red.”

ATS magnets are also located in areas where it is really unsafe for a train to speed – for example, coming into Gateway TC from any direction because of how busy it is, or the single track that goes into PDX International Airport.  These “speed trip” magnets have a pickup a set distance away from the magnet depending what the speed limit is, which activates the magnet for as long as it would take a train going faster than the posted speed limit to reach. So with a 15mph magnet, for example, if a train is doing 16mph when it goes over the pickup and doesn’t slow down, when it goes over the magnet it will trip it and come to a stop.  And again, the operator will have paperwork to fill out and explaining to do, because any type of ATS trip – from running a red or speeding – is a rule violation.

How a speed trip worksMore or less how ATS works for speed – let’s say that distance takes 30 seconds to cross if you’re going 15mph. If you operate a train through it and it only takes you 25 seconds, you’re speeding, and that magnet will stop you.

Although new operators especially don’t like the magnets since it’s hard to remember the speed limits of all parts of the alignment at first (and therefore easy to get tripped!), they are an extremely important safety feature and it’s a very good thing that they’re there – they prevent collisions in ABS territory (which covers all high speed areas) because a train will come to a stop at the red light, long before getting close enough to the train in front of it to hit it. And they prevent derailments or other accidents in areas where speeding would be extremely dangerous.