Tag Archives: rail car

MAX coupling

Not dead. Just resting.

Coupling Info and FAQs

This is going more in-depth on an old anatomy post where couplers were mentioned. The coupler at the end of each MAX car (with the exception of the A-end of a Type 4) allow for both a mechanical couple and an electrical couple between cars. The mechanical couple is what physically keeps the cars connected, and the electrical couple is what allows the cars to communicate. By design, both a mechanical and electrical couple need to be established in order for the train to move.

Although the Type 1s, 2s, and 3s are capable of being coupled into consists longer than two cars, MAX trains do not run in longer consists longer than that. There are rare exceptions to this (e.g. getting a disabled train out of the way), and yes, some 20 years ago trains were brought back into the Ruby Yard in longer consists but the length of city blocks downtown and the subsequent design of all the train platforms limit the length of MAX trains to two cars.

Note: There are several categories of TriMet employees who are qualified to couple and uncouple cars (operators, supervisors, mechanics, etc) but for simplicity I’m just going to go with “operator” in this post.

The Electrical Couple

The coupling process won’t make much sense without describing this first. At the top of the coupler is the electrical coupler head. Under normal conditions, this is either coupled to another train or covered, but occasionally one with the cover up will sneak through ground inspection without being noticed (or alternatively the operator will forget to switch it back after uncoupling cars).

Electrical coupler head on a Type 2 with the cover raised

There are two positions for the electrical coupler head – electronically isolated and electronically normal. If one or both electrical heads between coupled cars are in the isolate position, there will be no electric communication between the cars. When coupling cars, the first goal is to establish a good mechanical couple, and to do that the car doing the couple will be electronically isolated at the beginning of the process.

This switch inside the cab controls the electric coupling of the train

Coupling cars

First, as with just about everything else done with the trains, the operator will get permission from Control before coupling. Next, they’ll do a ground inspection of the car they will be coupling to in order to ensure there aren’t any safety concerns, such as personnel working on or around the car. They will also make sure that the car they are going to couple to is set to electronically normal. The operator will make three safety stops in the coupling process (because hey, you’re essentially about to drive one train into another train) – the first one car length away from the car being coupled to; the second about 10 feet away, and the third at about 3 feet away to ensure that the couplers of both cars are aligned. Then very slowly, the operator will bring their car forward and couple mechanically to the other car (this happens automatically).

The operator will then perform what’s called a “tug test.” As mentioned in the last section, the car that the operator is in is electronically isolated. When there is no electrical communication between the trains, the brakes will apply. In a tug test, the operator remains in the coupled cab and attempts to put the train in reverse and move. The test is a success if the cars do not move – this shows that the mechanical couple was correctly done because it’s holding the operator’s car (which should otherwise be moving backward) to the car with the brakes applied. If the operator’s train car moves backward, it’s either because the mechanical couple failed and the cars came apart, or the cars were not electrically isolated. A visual inspection of the couplers will also be done.

Next is the “trainline test” which is also done from the coupled cab. The operator will now set the car they are in electrically normal (remember that the car they coupled to is also electrically normal). Now there should be communication between the cars, and the easiest way to test this is to open and close the doors. In the yard, this will be done on both sides of the train, and the operator will watch to see that the doors in both cars open. On the mainline, this will only be done on the doors that are on the platform side for safety reasons. If the trainline test is successful, the coupled cars are ready to go.

The finished product: Two successfully coupled train cars. Note how the electrical coupler heads are raised and the covers are on top of the coupler. When the cars are separate, those will slide down over the electrical head.

Uncoupling Cars

A simpler process – again, always done with permission from Control. The operator will do a safety inspection and then press the “uncouple” button in the coupled cab (pictured in the first section of this post, it has a cover over it to prevent it from accidentally being pressed). Next the operator will back their car from the other one to separate the mechanical couple.

Mainline uncoupling

Uncoupling on the mainline is not preferable, but is sometimes necessary in order to cut a bad car and leave a “sportscar” train in service. The exception to this is, of course, the Type 4s, because they can only be fully operated from one end so they can’t be uncoupled on the mainline.

And then the 4s

The coupling and uncoupling processes above apply to the Type 1s, 2s, and 3s. The 4s are more complicated – as you can see in the above picture, they don’t match the coupler heads of the rest of the fleet. Under each Type 4 cab (the A-end) is  a fold-out mechanical coupler head which can be used to mechanically couple a 4 to any other car to be towed or pushed. Type 4s can’t be electrically coupled to the other types of cars, and are the only cars that have the step of connecting the canon plugs of the cables on either side of the mechanical coupler head to electrically couple.

Mechanical coupler head under the A-cab of a Type 4


What’s that bag over the coupler head? (seasonal)

These covers basically work like shower caps and are put over the coupler heads in snow/ice conditions to prevent ice from building up on the couplers. Metal covers used to be used but I don’t remember how long it’s been since they were.

Why is a coupler off-center?

deformation tube bend

The coupler heads are designed to be able to bend around curves in the alignment, so if you see a coupler like this, it isn’t broken. They should be straightened out during a ground inspection, but sometimes one gets missed. The operator or a supervisor will move it back into place when they see it.

What happens if the train cars come apart?

If that were to happen, they stop – the default position for a train car is “stopped” and the loss of electrical communication will apply the brakes in the trailing car, much like how the tug test works. I’ve heard some people are not comfortable riding in the trailing car due to “runaway train” fears if the cars separate, but the purpose of the tests done after coupling is to ensure that that doesn’t happen, so this isn’t something passengers need to worry about.

Today I learned: The more you write the word “coupler,” the weirder it looks.

Improving transit speed part 1

Over at Portland Transport, EngineerScotty (also author of the Dead Horse Times) posted on improving transit speed downtown, particularly for MAX. It’s an interesting post and a lot of different ideas have come up in the comments. I was going to respond there but it got long, so I’m taking it here and breaking up my thoughts on the different suggestions that have been made.

The first of these…

Train Length

One of the constraints of MAX brought up in the post is train length – Portland city blocks are about 200 feet, and a two-car consist is about 184 feet (191 feet if it’s a Type 4). All lines run through downtown, so the system is designed around that 200′ maximum length for trains. Early on in the thread, one commenter asked why we couldn’t run a train that’s twice as long (a four-car consist rather than the two-car consists run now) – even if it blocked a street while it serviced a stop, it wouldn’t be there long and this would double the capacity of service.

Dead Car PushThe exception, not the rule

Mechanically speaking and not taking anything like platforms into consideration, the cars are capable of being coupled together in consists longer than a two-car train. I haven’t really posted about how cars are coupled aside from answering questions in comments, but the trains are coupled in two ways: a mechanical couple and an electrical couple. The mechanical couple is what physically holds the cars together; the electrical couple is what lets the cars talk to each other. For example, this allows the operator to hit the door open button and have all the doors in the train open, not just the doors in the car that the operator is sitting in (this is called “trainlined” and yes, that’s where the safety communication gets its name). That works if there are two cars coupled together, or three, or four. I don’t remember if more than four cars can be electronically trainlined. This does not work for Type 4s. The coupler head located under the cabs of those is there to be used for a dead car tow or push and is capable of being mechanically coupled to any car in the fleet, but there will be no electrical communication between them.

Screen shot of Bob R’s video of the A-cab coupler head

So aside from the 4s, more than two cars could be coupled together and still function. However, there are a number of reasons why it would take so much money in construction costs to run 3-car or 4-car consists to the point where it’s just not worth it.

For one, the previously-mentioned trainline opens all the doors of the train. Assuming you have a four car consist downtown, if the operator stops to service a platform (we’ll use Pioneer Square North as an example), the rear two cars are going to be blocking SW 6th and going back up the block between 5th and 6th. When that operator opens the doors, all of the doors in the train are going to open, and remember that even on the low-floor cars, there’s a drop to the ground below when not at a platform:

Climbing into a Type 2 from the ground

So that would be opening the train doors onto the street, and even for people not using mobility devices, that’s not a comfortable way to get on or off the train. And to lengthen all of the platforms in the system to accommodate longer trains would be prohibitively expensive (just the Washington Park stop alone would be a logistical and financial nightmare)

There’s also the matter of what to do when the train gets to the end of the line.

In the Jackson turnaround

Here at Jackson St, which is currently the end of the line for Yellow and Green trains, the first and third tracks are big enough to accommodate a two-car train, but nothing larger. The circuits in the turnaround are only big enough for one two-car train. I took this picture from the leading car looking back toward the trailing car, and the last wheel axle of the trailing car is just past the insulated joint on the eastern entrance to the turnaround. And the center track can only accommodate a single car train, such as the mall shuttle. In short (pun not really intended), there’s no room for a train longer than two cars here.

So that means no four-car consists on the Yellow-Greens, which is good because that would make things much more difficult for buses driving on the transit mall. What about on the Blue line? Cleveland has a tail track, so there actually is room at the east end of the line in Gresham. Heading out to the west side though, there’s a lack of space. Here’s a view of the platforms at Hatfield Gov Center, the western terminus of the Blue line:

Western end of the Blue Line

As Hatfield is now, there’s no room for a train longer than two cars – to lengthen the platforms would mean shutting down Main Street which runs behind the building there.

It’s not just a lack of space and platforms big enough to accommodate them that that make it impractical to run longer consists.

Paradoxically, longer trains would actually mean slower running speeds in many sections of the alignments. At Goose Hollow (above), for example, the speed limit around that curve for eastbound trains is 10mph, and a train can’t accelerate until the entire consist is clear of the curve. You get thrown around quite a bit if you’re near the back of a trailing car going around a curve and the operator accelerates before you’re out of the curve.  If the trains were twice as long as they are now, that’s waiting until another 200′ of train has gotten through a curve before the train can accelerate.

In other places, gravity would work against longer trains. For example, heading into the tunnel westbound, the speed limit is 55mph past the first cross passage. As things are now, if your train is a two car consist with a crush load of people, it’s hard to get to 55mph since you’re climbing a hill with all that weight. If you’ve got twice as many cars and people, it’ll run even slower. Longer trains might mean more capacity, but ultimately they’d mean slower running speeds.

So it’s an interesting idea to run longer trains, but it would involve so much construction to existing platforms, major modifications to city blocks in the CBD, to say nothing of the work involved in changing the circuits in the rails to accommodate longer trains that it’s not feasible to do.

More to come.

Stop (and go) – Part 2

More on light rail braking, which was a surprisingly hot topic – I didn’t realize that dynamic braking on light rail cars would be that interesting in the blogging world, but there we are. Anyway, a belated hello to the people coming over from Reddit.

Disc brakes, also known as Friction brakes

In my last post I mentioned that dynamic braking is the primary method of braking at speeds greater than 3 miles per hour. Slower than 3mph, the dynamic braking blends with the friction brakes. This is because at speeds that slow, the motors-acting-as-generators can’t generate enough power to actually stop the train – remember that dynamic braking works by converting the motion of the train into electricity. Not enough motion = not enough stopping power. So at about 3mph, the friction brakes are applied, and ultimately these stop the train once the dynamic brakes have slowed the train enough.

The friction brakes are located underneath the train on the wheel axles.

Friction brake on a wheel truck in the shop – it’s the part that kind of looks like a sideways Coliseum in the middle

Here is a better un-blurred picture of the friction brakes. Actually all of the photos in that set are worth looking at if behind-the-scenes train stuff is your thing, and considering that you are presently reading a blog entry about the braking systems of light rail vehicles, it probably is your thing.

Inside the cab, the operator can tell if the friction brakes are applied or released with this indicator light, found in Types 1-3. It’s lit while the train is in motion above 3mph because the brakes are released. This indicator goes dark only when the brakes are applied. In the Type 4s, a similar indicator is lit only when the brakes are applied, and is dark when the brakes are released.

If you’re outside the train or in the cab looking at the mirrors, you can tell when the friction brakes are applied by watching the red brake indicator lights above the wheel trucks (Types 1-3) or over the doors (Type 4).

In this animated gif of a train stopping at a platform, you can see the brake light which is above the second passenger window from the door come on as the train almost comes to a stop, then it goes dark again when the brakes are released as the train moves up a bit (probably because the operator stopped on the dead spot) and then back on as the train comes to a final stop to service the platform.

Exterior brake indicator lights, Type 3 & Type 1

Exterior brake indicator lights on a Type 4

On a Type 4, the exterior brake indicator lights are located right above the door open indicator lights – the red light is the brake indicator and the yellow light is the door open indicator. Looking at a stopped Type 4 when the doors are closed, only the brake indicator lights will be lit.

The exception to the rule – brakes applied, but the indicator lights are dark

The exterior brake indicator lights will be dark if no operator is keyed in to the train even though the brakes will still be applied. This can be a useful thing for passengers to know – if you’re running to make a stopped train at the end of the line and you don’t know when it leaves, check the brake lights. If they’re dark, the operator hasn’t keyed in in the cab (and might not even be in the train yet) so you still have some time. If they’re lit, the operator is in the cab so the train will be leaving shortly.

Friction brakes work on a hydraulic system. Occasionally a friction brake will “hang” and will be stuck applied. When this happens, the operator can manually release the brake by pumping off the hydraulic fluid. This is what those boxes labeled “MRU” or “brake release unit” inside the trains are for – this is the manual release unit. The whole procedure for releasing a friction brake is very different in the Type 4s – you can see some of it (how the brakes are pumped off) in this video from earlier this year when a Type 4 had mechanical problems at NE 60th.

Track brake

Track brake on a Type 2

This one I have mentioned before – the track brakes hang between the wheels. The operator applies this to assist in stopping the train, typically on slippery tracks. This is also the brake that will be used in case of emergency during a dead car push. Because it rapidly brings the train to a stop which can be jarring for passengers, it’s not used in normal platform service unless the slippery condition of the rail warrants it.

Trivia: From a speed of 55 miles per hour, a MAX train will take about 600 feet to stop.


Question: Can trains get flat tires?

Someone apparently found their way here searching for the answer to this question. I hadn’t answered it yet, so here it is now. The answer is yes, sort of – a train will not get flat tires like a car can, but train wheels can develop flat spots. You’ll know if you’re on a train with a flat because it will sound like this:

Westbound into Sunset TC, sitting over the C truck of a Type 4 that had a flat

The trains should run pretty quietly – a “chugging” sound like that is indicative of a flat.

Flats can form on slippery rails or when the train makes a sudden hard stop, and bad flats on a train will get it pulled out of service so the wheels can be repaired.

Anatomy of a MAX car, Part 2

Train Car Anatomy, continued.

Coupler head

bullnoseThis is a Type 2, but the setup looks more or less the same on the Type 1s (and the coupler heads that fit these are folded under the cab of the Type 4s).  Under here you can see the bell, and then at the bottom going horizontally across the tracks is a bumper that prevents something that the train hits from going further under the train. The coupler head (bullnose) is at the end of a deformation tube which allows a coupled train to bend around curves and is collapsible in case of a collision.

deformation tube bendThis should’ve been straightened out as part of the ground inspection, but if for whatever reason this car needs to be coupled at this end, an alignment check is part of the coupling process that’s done to ensure that the deformation tube is straight


CyclopsEastbound approaching the Fair Complex as a westbound train is leaving.
Bonus – rainbow!

The cyclops, sometimes called the railroad light serves two purposes.  One, helps the operator to see in the dark. Two, clearly identifies you as a train! A foot pedal inside the cab lets the operator turn the cyclops off – this is used at night when passing other trains (or buses on the Steel Bridge) the same way you turn your bright headlights off when passing other cars on the road so you don’t blind oncoming drivers. Many operators will also kill the cyclops when they’re stopped at a platform at night so that in the event a train passes through in the other direction, their light is already off.


anticlimber, type 2

I’ve never seen one of these in action, nor do I particularly want to…  in the event of a train-train collision, the anti-climbers theoretically lock together and prevent one train car from climbing the other. The type 4s have these too, but they’re hidden underneath the shell that covers the coupler head. A combination of the ATS magnets, rail operator attentiveness and skill, and good direction from rail control is what prevents these accidents from happening in the first place (and therefore no need to test the integrity of the anticlimbers on our own any more than you want to test the integrity of your car’s airbags on your own)

And let’s take a look at the bottom of the train:

This is from a couple of years ago when a train derailed downtown – ordinarily you won’t see the wheels on a MAX car like this – they’re covered with a panel called a skirt. But the skirts were taken off this train in order to get it back on the rails, so now you can get a nice look at the wheel trucks.  That rectangular thing between the wheels (that in this picture is pressed against the ground) is the track brake. This heavy magnetic brake normally hangs just above the rail.  When the operator uses it, it makes a sort of clunking sound as it drops and a beep that you’ll hear if you’re sitting up by the cab, and it quickly slows the train down, stopping the train if the brake is continuously applied. It’s often used coming into platforms on slippery track surfaces such as leaves, ice, or water to stop the train. And of course, the wheels are found here.

In that above picture, the sanding tube is visible (it’s sort of visible in the first picture in this post of the coupler head just behind the bumper, though on the Type 2s and 3s it looks more triangular). You’ve probably seen the sandboxes on the trains even if you never thought much about them. I’ve been asked a few times what those are for.

Sand boxes in a Type 2 under the seats

Sand is automatically deployed to give the train better traction – it makes a sort of buzzing sound. You’ll notice this when the rails are wet, especially when trying to pick up speed going up a hill (e.g. entering the tunnel westbound from Goose Hollow).

track brake, wheels, sanding tubeWheels, track brake, sanding tube (visible on right)

Maybe I’ll add more to this anatomy… maybe not..  there are a few things I didn’t get into but it’s getting harder to find the time to blog these days and there are a lot of other things I want to write about.