Tag Archives: abs

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.

Signal Series – ABS Part 3

Where you will find ABS signals

I’ve mentioned “ABS territory” in the last few posts – most of the alignment is in that category.  In ABS territory, trains have a dedicated right of way and intersections are protected by crossing gates.

You’ll see signs on the alignment saying “BEGIN AUTOBLOCK” which designate entering ABS territory from pre-empt territory, and “END AUTOBLOCK” which designate leaving ABS territory and entering pre-empt territory.  One example –

E 102nd Ave Begin AutoblockE 102nd Ave looking westbound – beginning of ABS territory

which extends through…

AutoblockJust east of Lloyd Center – end of that particular segment of ABS territory which extends along the Banfield

ABS territory includes:

ABS territory mapAreas in green are ABS territory

Note: the above map isn’t perfect – there are some platforms on the border of ABS territory that have pre-empt signals in one direction & ABS in the other – and then a platform such as Lloyd Center isn’t in ABS territory, but leaving Lloyd Center eastbound there is both a pre-empt and an ABS signal – Goose Hollow is also similar, except there is both an ABS and a pre-empt going westbound. But the map should give you an idea at least.  From west to east:

Westside Blue Line – 12th & Washington westbound through the tunnel is ABS territory. Goose Hollow westbound also is ABS.

On the Yellow Line -the Vanport Bridge after Kenton/Denver and points north

Red, Green, and Blue – from points east of  Lloyd Center through the airport (Red), Clackamas Town Center (Green), and Gateway (Blue)

And for the Blue Line – Ruby Junction and points east.

Signal location

All ABS signals and combination signals (more on that in a later entry in this series!) are numbered to make them easy to identify and for operators to use when reporting their location to Rail Control.

On the Blue, Red, and Yellow lines, signal numbers correspond to their distance from the 11th Ave terminus downtown.

And point of trivia (not like this whole blog isn’t trivia, but whatever) – most eastbound main signal numbers end in 4, most westbound main signals end in 6.

Blue Line – east side

Signal 138, Gresham City Hall westbound – roughly 13.8 miles from 11th Ave

The signals east of the 11th Ave terminus on the Blue Line alignment have no designating letter, but the signal numbers increase as you head east from 11th Ave, and the numbers give you an estimate of their mileage from the 11th Ave terminus up to Signal 160, which is used by trains leaving the tail track into the Cleveland Avenue platform.

Blue Line – west side

Signal W1056 – Elmonica westbound, just over 10 and a half miles from 11th Ave

The numbers of signals west of 11th Ave terminus all begin with W and go up to W1778, which is one of the signals to leave Hatfield Government Center, nearly 18 miles from 11th Avenue.

Yellow Line

N60Signal N60, located at the Expo Center

Signals along the Yellow Line alignment from Interstate Rose Quarter through Expo Center begin with N2A and N2B, and go up to N62 at the Expo Center, a little over 6 miles from the 11th Ave terminus (I know these maps aren’t perfect, they’re just to give an idea of location and distance).

Signal numbers on the Red and Green Lines correspond to their distance from Gateway

Red Line

Signal A550 – Airport Terminus

On the Red Line airport alignment, the signals begin with A – the lowest number is A88 (which is visible to trains heading into Gateway) and they go up to A552 which is one of the two platforms at the PDX Airport Terminus. These numbers don’t relate to the distance from 11th Ave terminus – they correspond to the distance from Gateway, which is about 5 and a half miles away.

Green Line

C94Signal C94 – SE Main Street southbound

Signals along the Green Line alignment to Clackamas Town Center begin with C. These go from signal C14 near Gateway where the Green Line diverges south up through signal C630 which is the tail track signal at Clackamas. Again, like with the Red Line Airport extension, these numbers correspond to the distance from Gateway rather than the distance to 11th Ave.

Downtown Mall

M176ASignal M176A – Jackson turnaround

The ABS and combination signals on the downtown mall begin with M, beginning with the M176 signals in the Jackson turnaround and going up to the ABS & combination signals near Union Station and on the Steel Bridge (M16 is the lowest signal number at the Steel Bridge).


That pretty much covers ABS signals I think…  up next, pre-empts!


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.

Signal Series – ABS, Part 1

ABS Signals – An Introduction

There are a few posts I’ve been putting together, but I realized that an overview of the signal system on MAX was really needed in order for the posts to make sense.  Putting all of the signal descriptions in one post would be information overload, so here it is in (hopefully) easy-to-digest segments.

I’m starting with  the Automatic Block Signal System, or ABS for short.  A lot of the MAX alignment uses this type of signaling.

Blocks, Aspects, and Indications

Before describing the details of the signals, let’s cover some of the terminology. If you didn’t click on the above link explaining what ABS does, the briefest explanation is that it’s a system of rail signals that gives information about the alignment ahead of you, including how the switches are set and if there is a train in front of you.

An important concept to understand is a “block”. It’s pretty straightforward – a block is the distance between two ABS signals. The exact distance that a block cover in terms of miles/feet/etc can vary, but no matter how long or short it is, the distance between two ABS signals is always one block. Once you pass a signal, you’re in a new block until you pass the next ABS signal.

Onto the signals themselves – the most important words associated with these are aspects and indications. An aspect is the part of the signal that is lit. In other words, the part that’s considered a “light” to car traffic. So while in your car you have a green light to go, a train will have a green aspect.

And an indication is what that aspect means. For example, when a train has a red aspect on a signal, its indication (what it means) is STOP.

So here’s a basic, one-headed ABS signal that can display 3 aspects:

Stop, signal 22Red aspect on signal 22, Lloyd Center eastbound

A red aspect on this signal (as shown) indicates “stop.” That’s the easy one!  This picture was taken right after a train left Lloyd Center heading eastbound, and it entered the block that is between Signal 22 and the next signal. If a train came into Lloyd Center right now and saw this red aspect, they would know that meant that the train in front of them is still in that block. Therefore, that following train is not clear to proceed past it until that first train has moved into the next block.  At that point, the signal will become…

signal 72Yellow aspect on signal 72, Gateway westbound

A yellow aspect on this signal indicates “clear for one ABS block on the primary route” – meaning from this signal to the next one, there are no trains there. However, in the block after that, there is a train there (so the signal after this one will be red until that train leaves).  When a rail operator passes a yellow ABS signal in a high speed area, such as coming out of the tunnel going westbound, they won’t bring the train up to the full speed limit because the next signal will be red, so they will slow down giving the train in front of them time to clear its block.

W754Green aspect on signal W754, Beaverton Transit Center eastbound

A green aspect on these signals indicates “clear for two ABS blocks on the primary route” – meaning not only are there no trains between this signal and the next one, there are also no trains between *that* signal and the one after it.

Here’s another way of looking at it:

Green ABS diagramYou are the operator of the train on the left side of the picture.  The direction of travel is from left to right, and there is a train in front of you.  There are two ABS blocks between you and that train, so the signal you will see will be green.  You proceed through it and enter that first open block.

Yellow ABS diagramIf that train in front of you hasn’t moved, when you get to your next signal, it’s going to be yellow.  This lets you know that you have one open ABS block clear between you and the other train.  You proceed through it and enter the new block.

Red ABS diagramIf that other train still hasn’t moved, when you come up to the next signal, it will be red.  This tells you that the block in front of you is still occupied by your leader, and you are not clear to proceed past this signal into that block.  Two trains cannot occupy the same block at the same time, so you must stop until you get a clear to proceed.

Some ABS signals, like this one, can only display 2 aspects. That means there is a platform in the next ABS block.

Two aspect signalYellow aspect on signal W1534, Fair Complex eastbound

So there are no trains between you and the next platform (which is Hawthorn Farm) – there may or may not be a train in the block after that platform, but there will be another signal there that will tell you that information when you get there.

There is also one more aspect that some ABS signals can display – the lunar aspect:

Signal 14, lunarLunar aspect on signal 14, Steel Bridge westbound

This one can be a little confusing – it indicates “Proceed with caution, tracks may not be clear.” This one will tell you how your switches are set and which route you are going on, but it does *not* tell you if there is a train ahead of you. Although this is an ABS signal, it is used in pre-empt territories and sometimes at the border between ABS & pre-empt territories- you’ll see lunars at both the Hatfield terminus and the Jackson turnaround as well as on the Steel Bridge, which are all in pre-empt territories. Lunars also are used to move Blue Line trains from Gateway to Burnside and from Burnside to Gateway.

Up next – more with ABS signals!