Slow times at the Steel Bridge (and what the cones are for)

Lots of people wondering lately:

Have we been going even slower than usual on the Steel Bridge?

Answer: Yep.

Eastern side of the Steel Bridge span

Current speed for trains over the Steel Bridge span is 5mph instead of the usual 10mph. I’d mentioned this way back when in the “How fast do the trains go?” post – the speed over the Steel Bridge span is typically 10mph in order to (relatively) reduce vibration while crossing the span, which can damage the microswitches & sensors and other mechanisms on the bridge. I say “relatively” because if you’ve ever walked over the upper deck of the bridge at the same time a train is crossing it, you can feel the effect it has going over the span even at 10mph.

But a few Sundays ago, the speed was reduced to 5mph on the span because some of the sensors on the bridge had gotten damaged, and a slower speed means less vibration. At that time, a train order was issued directing trains to proceed at this reduced speed. Since a train order can only last for 24 hours and this was going to last longer than that, a special instruction (which can last for up to a year) was then issued until everything gets repaired.

Within a few days, the cones were placed on the bridge to mark the area affected by the slow order. Ignore the green cone in the above picture for a moment – the yellow cones, which are placed in pairs 100′ apart, indicate that speed is reduced over the span. As soon as the front of the train reaches the first yellow cone, it must reduce speed to the necessary level (5mph in this case) and maintain that speed until the front of the train reaches a green cone on the other side. So in the above picture, the green cone is for eastbound trains and the two yellows are for westbound trains.

A similar arrangement is on the western side of the span, though only one of the yellow cones is visible from this angle because of the grade of the bridge and the concrete divider.

The green cones are placed 200′ from the span. That’s the length of a train, meaning a train can resume normal speed there since it’s clear of the span once the front of it reaches that spot. You may have seen the word “CLEAR” on the bridge about 200′ from either side of the span which predates the cones being used for this current special instruction. That lets you know under normal operating conditions that the usual CBD speed of 15mph can be resumed once the front of the train gets to that point.

I have an old post showing a view from the cab crossing the Steel Bridge eastbound if that helps with the visuals.

Cones and Flags

The cones are nearly functionally identical to wayside flags, which have been mentioned in this blog before. Flags with pointed ends are used in ballasted track, flags on tripods are used on paved t-rail, and cones are used in low-speed paved areas. The tunnel uses flags that are attached to the handrail on the walkway, but I don’t have any pictures of those.

Slow order wayside flag in ballasted track

There are some differences between how cones and flags will be arranged for use. In areas of the alignment that use flags instead of cones, only one yellow flag is used for a slow order unlike the pair of yellow cones used in low speed paved areas. Where flags are used for a slow order, trains must be at the ordered reduced speed when the front of the train reaches the yellow flag. Similar to the cone arrangement, trains will maintain that speed until the front of the train reaches a green flag.

Another example of cone/flag similarities:

Double red cones on Holladay Street during Streetcar tie-in work last fall indicating that this track is out of service…

… have the same meaning as these double red wayside flags (photo from expansion joint work on the Yellow Line last spring)

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.

The 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.

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.

Restricted Speed

And for today, a definition.

Restricted speed for a MAX train is:

20 miles per hour or the posted speed (whichever is less)

but always at a speed that would allow the operator to stop within half their sight distance.

Thick fog at night limiting visibility

So for example, downtown where the speed limit is 15 mph, restricted speed would never be faster than 15, but in areas where the normal speed limit is faster, restricted speed will be a maximum of 20 mph. Conditions like thick fog that reduce how far the operator can see ahead will likewise reduce the maximum speed permitted under restricted speed.

Situations in which restricted speed would be used include -but are not limited to- any time a train is running reverse traffic (e.g. east in the westbound tracks) or after bypassing a red ABS signal, or as directed to by Control.

EDIT – I’m updating this post with clarifications after being contacted via email which made me realize I’d worded some of this unclearly. Under normal operating conditions, something like a foggy night could get a warning from Control that you should operate at a speed that you feel comfortable and safe going at, which does not mean restricted speed – if the speed limit through a foggy area is 55 but you feel safe at 40 or 50, that’s fine. It is only when Control has stated that you should operate at restricted speed that the 1/2 sight distance restriction comes into play.

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.