Tag Archives: ats magnet

Manual blocks and reverse traffic

I recently was asked some questions about

Manual blocks

(and this post got long… you might want to go make a nice sandwich or something for yourself before settling in to this one)

When train movement on one track is not available, a manual block is used to move trains on the adjacent track. This could happen because of planned maintenance, or it could be done in the event of an accident/emergency situation. In a manual block, Control directs train movement in both directions on the track that is in service. Manual blocks will have associated train orders.

You’ve done the equivalent of a manual block in your car before if you’ve gone through road construction where only one lane is open. For cars in that setting, there’s a flagger at each end of the construction area that lets a number of cars through and holds oncoming traffic from entering the single lane, and then they switch to let cars from the other direction go through. A manual block for trains is essentially the same idea – Controllers and supervisors coordinate to govern train movement into a manual block, alternating between trains running normal traffic (e.g. east in the eastbound) and others running reverse traffic (west in the eastbound).

Reverse traffic

Borrowed photo. This is not a manual block, but it shows a train running reverse (here east in the westbound at Willow Creek)

Running reverse traffic is not the same thing as backing a train up. An operator backing a train up (such as in the case of uncoupling a train car) can’t see in the direction that the train is moving – this is why backing a train up is almost never done. When an operator is running reverse traffic, they face in the same direction as the train’s movement, but that movement is in the opposite direction of what the track they’re on is typically used for.

There are a number of rules that govern running reverse traffic. First, it’s always done at restricted speed (the lesser of 20mph or the posted speed and always at a speed that the operator can stop in half their sight distance) whether or not it’s part of a manual block, unless you’re in the tunnel. Because the tunnel is signalized in both directions, trains running reverse can operate at the posted speed limits which are about the same as normal speed limits, though trains going west in the eastbound bore will exit the tunnel much slower than normal traffic because they will be diverging into the west portal pocket track. Other areas of the alignment that are signalized in both directions are already single track, e.g. the “fishhook” for the Red Line at Gateway, so travel in both directions is normal.

While running reverse, operators will also have to stop and observe every set of switch points to ensure they are properly aligned. In ABS territory, running reverse traffic is where dwarf signals come into play – they protect mainline power switches while running reverse traffic. In other words, the ATS magnets associated with the dwarf signals are active for trains going the “wrong way”. Operators will have to key-by these signals (this is done from the operating console in the train cab) after calling Control. This gives the operator 23 seconds to move the train past the ATS magnet without tripping.

On Burnside, operators running reverse traffic will have to SOP the intersections since the mass detectors are only for normal traffic. If the reverse running on Burnside is part of a manual block, the train orders associated with the manual block will include instructions to SOP intersections within the block. So operators will not need to call Control for permission at those intersections, but otherwise the process to SOP them is the same – stop, wait for fresh parallel green and walk signal and red left turn signal, sound horn warning, and proceed when safe.

You may have seen these stop signs at gated intersections or in places where the view is obstructed by a substation building – these are for trains running reverse traffic since people are not likely to expect a train from that direction on that track.

Gated intersections are also handled differently when running reverse traffic. When running normal traffic, the gates are lowered either by a call loop if the platform is right near the intersection (such as the above picture of Elmonica/170th) or when the train enters the approach circuit as it approaches the crossing gate for gates that are not near a platform. There is another circuit that extends 10 feet on either side of and through a gated crossing called the island circuit. When the island circuit is shunted, it will lower the crossing gates if they weren’t already lowered – you won’t notice this running normal traffic since under normal operations the gates will be lowered by the time the train gets there, but when a train is running reverse traffic, it uses island circuits to lower the crossing gates. The operator will wait until the gates have been fully lowered for 10 seconds before proceeding through the intersection.

Manual Block

In a manual block, most of the rules that apply to trains running reverse traffic will also apply to those running normal traffic. For one thing, travel in both directions of a manual block will be done at restricted speed, unless otherwise instructed by Control.

Borrowed picture – Both of these trains are running normal traffic, but it shows switch points as the operator sees them. Here it is a trailing move since the points are facing away from our oncoming train

If there are switches in the manual block, operators in both directions will be required to stop and observe every set of switch points before proceeding, regardless of whether the switch points are facing toward the train or away from the train (as seen in the above picture).

A planned manual block will have a written train order, but operators about to enter a manual block, whether planned or unplanned, will still call Control before they enter to receive specific instructions. The instructions will have to be repeated back word for word, which ensures that there is no misunderstanding of the instructions, since manual blocks have the potential to be extremely dangerous. Even at 20mph, a train splitting a switch (making a trailing move over a power or t-rail switch that isn’t set for you) or hitting another train can cause serious damage. The specific details of the instructions may vary depending on where the manual block is and why a manual block is in effect – for example, a planned manual block may have pullback operators to pull the train through crossover switches so that the operator of the train doesn’t have to change cabs.

Previously, a “medallion” system had been used for manual blocks. A medallion was an object such as a stuffed animal (like the rabbit) that would be passed off to a train as it was about to enter the block. If you didn’t have the medallion in your possession, you would not enter the block. Nowadays that system isn’t used. Instead, a clearance sheet is used to record all train movement in manual blocks. This written record details the movement of all trains into, through, and out of the block, ensuring that only one train is in the block at a time.

Once an operator is clear of the block, he or she will call Control. Their train will be recorded on the clearance sheet, and the operator will then be able to resume normal operation. The next train will then be cleared to enter the manual block. This process continues for the duration that the block is needed. At that point, Controllers and supervisors will ensure that all trains are clear of the manual block and that all switches are aligned normal and locked. The first train through the track that had been out of service may be asked to sweep that section of the alignment, especially if the manual block was due to an emergency, and then following trains can operate as normal.

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!

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.