Category Archives: brakes

Rock and rail

And now here’s an example of using the scanner for subjects other than fictional prostitute stings. By now you’ve probably heard about the incident a few weeks ago at about 5am when an eastbound train hit a large rock in the right of way near the Murray overpass between Beaverton Creek and Millikan Way.

I was asked on Twitter if this was something that the sweep train (the first trains through the alignment in the morning that run at a slower speed to check for debris, damage, etc) should have seen. However, the sweep train goes through there at about 3:30am, and four more trains follow it before the one that hit the rock, so it’s very unlikely that the rocks ended up there overnight and were somehow missed by five trains.

eastboundblueLooking east from the Murray overpass where this happened

Given the size of the rock (I think it took both the supervisor and the operator to get it out of the way) and my complete lack of detective abilities, I’m not sure if it was thrown from the overpass or whoever did it trespassed down in the ROW and left it there. Regardless, TriMet is looking for anyone who might have information and is offering a $1000 reward for information.

Coordination when things go wrong

When something goes wrong on a train, it can be very frustrating for passengers to not know what’s going on, why are we stopped, how long are any delays going to be, and so on. Generally speaking, operators are going to try to keep you as updated as possible because the last thing anyone wants to deal with on a stopped or broken down train is passengers redknobbing the doors and potentially getting hurt trying to leave! Unfortunately, sometimes the available information is limited and your operator doesn’t have any better idea than you do when things will be moving again.

Wait, let me say that one again: Unfortunately, sometimes the available information is limited and your operator doesn’t have any better idea than you do when things will be moving again.

Annnd, once more for luck: Unfortunately, sometimes the available information is limited and your operator doesn’t have any better idea than you do when things will be moving again.

Additionally, your operator isn’t just keeping all of the passengers informed, but he or she also has to communicate with Control, sometimes almost constant communication depending on the situation which means less time to convey information to the passengers. Consequently, it can seem like you’re sitting there wasting time while nothing is being done to fix the problem. This isn’t the case, it’s just that you’re most likely not going to be able to hear all of the coordination that’s done over the air to address the issue.

Because the rock incident happened very early in the morning, there wasn’t a lot of other traffic on the air and so the scanner got just about all of the related calls. I like this because it shows how the operator, supervisor, and controller worked together to get service going again with as little interruption as possible (also, no one was injured in this incident so I don’t think there is anything sensitive in any of the calls). Due to the relative simplicity of this event as compared to, say, the power issues from last week, the radio calls for this are pretty easy to follow along. If you’re interested in listening to how this played out but aren’t familiar with TriMet’s open air radio, you might find this radio refresher helpful – remember that when on the air, controllers don’t use an identifier, operators use the train number, and supervisors have four-digit call signs beginning with 95. In this incident, the train is 21, the supervisor is 9514 (both male voices), and the controller is the female voice.

Here are the highlights: The beginning of the incident is a little choppy (some problems with the radio where 21 couldn’t hear the controller), but the controller was able to understand that 21 hit an object in the ROW, so she called westside supervisor 9514, who is monitoring everything from Washington Park to Hatfield. 21 was able to get through with a description of what happened, and then relayed to the controller what problem indications he had in his cab (among them are friction brake faults - this will be important in a moment). Since this train was in service, the most ideal thing to do is to try to get it into Millikan Way where passengers can be safely offloaded if the train has to be taken out of service, and 9514 would meet up with 21 there to assist.

21′s follower, Train 22, is held at Willow Creek. This keeps the eastbound alignment from Millikan to Willow Creek clear, which would allow 21 to run reverse traffic (west in the eastbound alignment) if necessary back to the Elmonica yard. Meanwhile, 9514 meets up with 21 and sees a friction brake hangup in the A-truck of his lead car. For a quick refresher of what that means:

T3 & 1 brakes

These red lights on the outside of the train are located above each of the three wheel trucks (A and B at either end and C in the middle) in the Type 1s, 2s, and 3s. It’s a little different in the Type 4s, but I’m skipping that for now since this incident didn’t involve a 4. When illuminated, these tell you that the friction brake in that wheel truck is applied. You want this when the train is stopped, as in the above picture. You do NOT want this when you expect the train to be moving! So 9514 was able to see that the exterior brake indicator in the leading truck of the lead car was lit as the operator was trying to move the train into the platform, and he knew that this meant that friction brake was “hanging up”, or staying applied. The way to troubleshoot this is to pump off the hydraulic fluid from that brake and manually release it.

mru3MRU, Type 3

Each train car has an MRU, or “Manual Release Unit” where a friction brake can be pumped off. This is a fairly basic procedure that every operator learns how to do in training, but the standard procedure is for the controller to pull up a checklist to follow for consistency. After the train made it into the platform and passengers exited, 9514 was able to inspect the car for damage, including the leaking hydraulic fluid pictured above which explained the brake problem. If the only problem a train has is a hanging friction brake, it can continue in service with one brake pumped off, but you can’t do more than 30mph so it’s not really ideal. Any more than one brake pumped off and the whole train has to be taken out of service. In this situation, because the train had hit an unknown object and 9514 was still assessing damage, the train most likely wouldn’t remain in service even with the brake pumped off, but they needed to figure the best approach to getting it out of the way. The controller suggested that the best solution might be a dead car tow – that is, pump off all three of the friction brakes in the car and have it be pulled back into the yard by the other car.

9514 decided to begin pumping off the friction brake in the A-truck of the car – they’d have to do that anyway for a dead car tow, but it was possible that pumping off that one brake might be enough to get the train rolling. At this point in the radio calls, there is a lot of back and forth between the controller and 9514 as she read through the checklist and he carried out the procedures. After the brake was pumped off, 9514 confirmed that it was holding (i.e., it’s staying released), and the controller asked 21 to take a point of power from the eastbound cab. Although the train would be going back west to Elmonica, this is just a fast way to verify that the brake is no longer applied in that truck. She then told Train 1, the incoming westbound train at Beaverton Transit Center to hold there (remember that 22 has been holding back at Willow Creek, so this is leaving both the eastbound and westbound alignment clear from Willow Creek to BTC). 9514 said he’d ride back with 21 to see if he can find what had been hit.

runningreverseNot the train involved in this incident, but it’s a train running reverse – this one going east in the westbound at Willow Creek

Now 21 was running reverse back to Elmonica west in the eastbound alignment. If you want more info on what running reverse traffic means, I did a post on it a while ago, and other posts with related things you’ll hear if you’ve been playing the transmissions so far (such as needing to key-by a dwarf signal and running at restricted speed). 21 made a brief stop under the overpass to see what had been hit and try to clear it so that other trains could safely get through, and that’s when they found the rocks pictured above. They got them out of the way so that the westbound trains (Train 1 still holding at BTC) could get moving again. 21 then arrived at the yard limit and took the train into the yard so that normal train movement in both directions could resume. The whole thing took about half an hour from start to finish, though given the spacing between trains, it wasn’t a major impact to service.

But consider train 22 who was behind the incident train. They would’ve been around Fair Complex when this happened, and then holding at Willow Creek for about 15 minutes while all of this played out. If someone on 22 asked the operator when things would get moving again, there’s no easy answer to that – if you played through all the calls, you now have as much information as that operator did. There’s no secret operator-to-operator information service that gets additional information and a timeline out (though that would be cool). At best, the operator can explain the situation at a very un-detailed level because once you start getting into brake pump-offs and technical things, people’s eyes are going to glaze over. But if that procedure had failed or if there was serious damage to the train, or if 21 and 9514 couldn’t get the rocks out of the ROW, this would’ve taken longer, but there’s no way to know how things are going to go while the incident train’s operator, the supervisor, and the controller are working on it. So once again, unfortunately it’s very likely that your train’s operator isn’t going to have any better idea than you do of how long something will take to fix and get rolling again.

Overall I think this incident was a good example of what’s going on “behind the scenes” when something breaks down. Getting things moving as quickly as possible again is on the mind of everyone involved; no one’s doing this to get a kick out of passengers missing their (often infrequently) connecting buses (and on a self-interest side, no operator enjoys running late and losing part or all of a break due to delays!) There’s a lot of coordination between operators, supervisors, and controllers in every kind of service disruption, but unfortunately most of it is going to happen where passengers don’t see or hear it.

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.

Stop (and go) – Part 1

Someone found my site by searching a few permutations of “How do the Portland MAX trains stop?

I liked the question and so here’s your answer:

Multiple Brake Systems

Of course, it’s not going to be a simple answer. There are several brake systems on the MAX trains.

Dynamic braking

Dynamic braking is the primary method of braking used when the train is going faster than 3mph.

I’ve posted this picture before, but it’s helpful in this context so I’m posting it again – Reverser (on left) and Motoring Drum Handle (on right) of one of the low-floor cars. Click for larger version.

On a really, really basic level, you move the train forward by moving the motoring drum handle (MDH) into a propulsion mode, shown in green next to the MDH. This draws power from a substation through the overhead wires, which rotates the train’s motors and moves the train forward.

When you move the MDH into a braking mode (shown in red next to the MDH), that makes the motors stop acting like motors and start acting like generators. The function of a generator is to convert motion into electricity – think of wind or water generators that create electricity from the motion of the wind or water through them. So when the train is in a braking mode and the motors are behaving like generators, they take the forward motion of the train and convert it into electricity. This conversion slows the train down because the creation of electricity happens at the expense of that forward motion. This is a far more effective way to stop a train moving at high speeds than dragging something on the wheels of the train to slow it down would be.

But then what happens to that new electricity that was converted from the motion of the train?

In the Type 1s, that extra electricity is just given off as heat from the motors. It works, in that the train slows down which was your primary goal of braking, but it’s kind of a waste of that electricity.

The  Type 2s, 3s, and 4s, however use regenerative braking. I’ve mentioned circuits before in the sense of currents through the rails shunted by the axle of the train wheels. Now think bigger – a circuit going from a substation, along the catenary and down the pantograph to the train, out through the wheels and along the rails back to the substation.

More or less like that

When one of those low-floor cars slows down using dynamic braking, that created electricity isn’t just wasted as heat into the air. Those cars channel most of that energy back into that circuit, where another train can use it.

Think of it this way the next time you’re in a train braking to stop at a platform – if it’s not a Type 1, the extra electricity from your train slowing down is being sent back into the overhead wire. The next train can pick up that electricty created by your train and use it to propel forward instead of drawing all of its power from the substation. This is much more efficient, because the energy converted from your train isn’t completely wasted, and less power needs to be drawn from the substations when you take power from another train’s braking.

This blog discusses how regenerative braking works in detail with helpful diagrams if you are interested in a longer explanation.

More to come.