Pragmatic 71: Off The Rails

18 March, 2016


Trains and roads look like they have lots in common but the trade-offs in signalling and network design are completely different, and horrendously inconsistent.

Transcript available
Welcome to Pragmatic. [Music] Pragmatic is a discussion show contemplating the practical application of technology. By exploring the real-world trade-offs, we look at how great ideas are transformed into products and services that can change our lives. Nothing is as simple as it seems. Pragmatic is part of the Engineered Network. Network. To support our shows, including this one, head over to our Patreon page. It's at or one word. And for other great shows, visit today. I'm your host, John Chidje, and today I'm joined by Vic Hudson. How's it going, Vic? Good, John. How are you today? Very good. Very good. Thank you. Today, I'd like to talk about trains. Trains. Do you like trains? Yeah, trains. Do you like trains? When I was a child, I had curtains and a bedspread that matched that were trains. Oh, cool. My granny made it for me. Oh, that's lovely. See, I've always had a soft spot for trains and I had a request come in from a listener that wanted me to do an episode about trains. And I had a good long hard think about what it is about trains that I like so much. I have a love-hate thing for trains, I'll be honest. honest. But I guess, I've been on trains on and off for probably 20 years now. And it's in different countries around the world, different countries, but a few different cities around the world. Like I've done the ones in Sydney, I've done trams in Melbourne, I've done the trains in Brisbane, obviously, and light rail in Calgary. I've been for a spin on the Bart in San Francisco. Yeah, so a mix of different things around the world and and trains have been, I think, a pivotal change in our in our in Western culture, you know, for 100, 200 years. So I think trains are interesting, but there's only so much there's a lot to talk about with trains. So I want to try and narrow this down a little bit. And I also want to add that just a point of interest that all the notes that I'm about to read for this episode. And in fact, most of the episodes of Pragmatic and Causality were created, edited, modified, and the editing of the podcast was done whilst traveling on a train. So there you go. Alrighty, I mentioned trains and trams. Should probably just quickly clarify the difference. Trains, like as in heavy rail trains, they're big and heavy. Funny that, anyway, and they're used mainly for freight as well large numbers of passengers like really large like many many hundreds of passengers and they're defined by having dedicated tracks and the tracks only cross roads well and they call them railway crossings right and they don't actually share a road with other vehicle classes and mainly because they are very big very heavy and very dangerous so you want to keep them separate and they utilize block signaling and that'll make sense later when we talk about a little bit more due to the longer braking distances and and what- - They don't stop quickly. No, they don't stop in a hurry. No, when they get moving, they stay moving. So yeah, anyway, so we'll talk more about that later and multiple aspects signaling and all that other good stuff. Now, trams on the other hand, in North America, they're sometimes referred to as a street car or a trolley or a trolley car. So when I first went over there like, oh, a street car, I'm like, oh, really? A street car? That's a tram. No, no, it's a street car. Okay, whatever, same difference. You know what I'm talking about, anyway. So they travel on a combination of sort of exclusive access tracks like the heavy rail does, but they also importantly share lines embedded within roadways. Yeah, so you can drive behind a tram or a tram can drive behind you and scare the whatses out of you because it's this enormous tram and it's about to drive right up your rear end. Anyway, nevermind. So yes, light rail though. Freaked me out first time. Light rail is often implemented in sort of similar ways, sharing roadways with other vehicles, but the difference of the light rail is it more regularly carries higher passenger counts and it consists of multiple units connected together, whereas trams are almost exclusively singular units. So light rail of course being like trams is slower and it utilizes traffic flow signaling again talk a little bit more about flow signaling later and that allows multiple car multiple trains or light rail cars to stack up nose to tail and that reduces network congestion but you'll get to that in a minute. The thing about trams that I found interesting was that trams were only used for public transport much later than heavy rail and originally they were horse-drawn that was back in the early 1800s but the first electric tramway was opened in 1881 in Germany in Lichterfeld and was built by Werner von Siemens. Yep, Mr. Siemens. And I only find that funny because of course I spent a large chunk of my career programming Siemens PLCs. Yay Siemens. Anyway, S7-300s, baby. OK, the world's best PLC. Send the flames at me. OK. I talked to some control system programmers and they see Siemens as the enemy. Siemens is like some kind of poison and you can't understand how to program a Siemens PLC. They're all too funky with their OB1 and OB35 and all that. Anyway, it's kind of like a Mac versus Windows or an iPhone versus Android kind of thing. Kind of thing. Yeah, it's almost. Yeah, it is. But statistically, Siemens PLC is the world's most popular PLC, or at least they were five years ago. Don't know what I've seen the stats recently, but anyway. All right. Side track there. Go Siemens. Anyway, so some say it's a geek fight of the highest level. It's a geek fight and about the highest level, but definitely it's a geek fight. Okay. So, the funny thing is that a lot of cities have both or just the heavy rail or heavy rail and trams and different optimizations. So, some cities will use the trams for short haul and trains for long haul and that's what Brisbane originally did, but then, of course, they ripped the trams out. Yeah, I mean, ultimately, the trams didn't fare so well pretty much all around the world and I guess we should talk about the death of trams because in the US there's an urban legend or is an actual conspiracy? I'm not sure to be honest because I wasn't there but hey. Regarding General Motors and diesel buses. Have you heard much about this one? The National City Lines that owned and operated several streetcar subsidiaries? I don't think I have heard this one but I have heard some some conspiracy theories about some of the car companies killing off like electric vehicles and stuff. Oh that's another topic for another day but hey yeah yeah so I'm assuming we're talking about something similar yes we are absolutely and the thing is that there were there were actually were some indictments so let's just talk about that briefly because it's interesting sometime between 1938 and 1950 street cars all around America were being replaced gradually by buses. And even though nine corporations and seven individuals were indicted for, and this is the quote from the judge at the time, "conspiring to acquire control "of a number of transit companies "forming a transportation monopoly," end quote. That was in 1947. But the problem with the whole theory behind that was that many, many countries around the world also stopped using trams around about that time. And the reason simply came back to money. The mass manufacture of buses and their associated, therefore reduced running costs relative to electric trams, it just it simply made it difficult to financially justify something that was more niche and therefore more specialised to operate and maintain like trams. So, you know, because you have to maintain roads for cars, so putting a bus on the road is an incrementally small cost. Plus, the buses are mass manufactured and the trams were highly specialized, there weren't as many of them. So, if you look closely, most of the tram systems around the world that are still operating condition today, still servicing customers, they're all very heavily subsidized by the government. And the reason they keep them going, it's for more than just economic reasons, because if it was down to of economic reasons, they probably wouldn't run them. They're quieter, they cause less pollution and I honestly think they add character to a city, you know. And character is worth something, you know. I know I'm an engineer and I'm not supposed to think that but I do actually think that. I mean, the cable cars are still going. They say it's a tourist thing in San Francisco but can you imagine San Francisco without cable cars? I don't know about you but that just feels wrong to me. It doesn't feel, it feels like it would be a travesty if that ever happened. It's a very iconic image. Yeah, it is iconic. And having traveled on a cable car myself, you know, I totally get why. I think they're fantastic. Just that's the nostalgia in me speaking, but that's okay. Anyway. All right. So, now that we've talked a little bit about trams and the not entire death of trams and the resurgence of light rail, I guess a little bit, but yes, light rail is making a bit of resurgence. I want to focus on trains, though, because there's a lot more of them. Now, I've been taking trains, I think I said before, about 20 years now, and I've done a little bit of work, not that much work, but a little bit of work with Queensland Rail, which is the Queensland Railway Corporation. And that was as a subcontractor. That was many years ago now. Now, I've seen their control system and I've had many, many, many long conversations with signaling and rolling stock engineers over the years. So, when I say rolling stocks, I'm not sure if that's an Australian expression or not, I don't think so. Because in railway, in Queensland Rail, and I think most railway companies, they have different divisions. So, they'll have track, in the case where it's electrified, they'll have overhead and then they'll have rolling stock which take care of all the locomotives, carriages, you know, all the stuff that's rolling stock or rolling equipment on the rails and then you'll have signaling. So, pretty sure Queensland Rail, actually I'm really not sure that, I guess my information on how Queensland Rail is broken down inside is about 10 years out of date now because I'm getting old, I guess. No, I don't, I I guess I am. Anyway, so yeah, it's about 10 years old, but that's okay. That's the way it used to be split up. So anyway, I've spoken to signaling and rolling stock engineers predominantly. So I don't think I've ever met an overhead engineer or a track engineer before because I just haven't. Anyway, so in my hometown, I grew up in Rockhampton and in my hometown, there were two main professions when you graduated as an electrical engineer. You could go and work for Queensland Rail or you go work in the mines. And me being me, naturally I didn't do either, I just left the country. So there you go. (laughing) Screw this, I'm out of here. - I choose option C. - I'm making an option C, see you later. Anyhow, but then I came back, so there you go. So I've always been fascinated by the train architecture and I don't mean the train physical architecture, but I mean the network that it travels on. and I realize that I'm bordering on traffic engineering and network engineering a little bit, but it is fascinating. Well, okay, I think it is. So why am I fascinated by it? Well, let's see, because I've been stuck on a train, delayed many, many, many times, and I sat in the carriages, my head pressed against the window, looking outside, trapped, unable to escape, and wondering what the heck is wrong? Why is the train not moving? Anyway, so I thought about it and I thought about what's wrong with the train network architectures, why the networks grew the way they have. And that's what I want to focus on today. I'll talk about how the train networks have grown, changed, evolved over the many, many hundred years or so. And also a little bit about how the signaling works and some of the bottlenecks and some of the restrictions, because I think it's fascinating. So, OK, it all begins when someone wants to travel between two places in a town and they don't want to walk because they don't have a horse and they got sore feet. I don't know, whatever. Oh, they don't have one of those new fandangled auto whatsits, you know, automa thingies, thems, don't have one of them either because they're like really expensive. The car? Cars. Yeah, that's it. See, we don't have them, right? This is going back 150 years, right? So, and of course, you couldn't find a cabbie because cabbies are an absolute ripoff and you can't trust them either. They're probably just mass murderers. So, never mind that. Wow. And there was no Uber. It was Uberless. I can't find me no Uber. So, what am I going to do? Before there were buses, the mass transit solution was the train. And obviously, we've talked about trams and light rail and heavy rail and all that. I don't want to go into that again. But yes, I've acknowledge there are differences. Anyway, so again, heavy rail is mainly designed for moving around large numbers of people or large amounts of freight, but because it's not so fast, it won't handle acceleration or deceleration as well as light rail will. So, it's not such a good thing for a suburban network that's got lots of starting and stopping. You know, light rail does the opposite, which is why it's having a bit of a resurgence for the inner suburbs. It's light, faster, quicker, cheaper to build, doesn't need as much ballast which is the all the rocks and the stabilizing, gosh, the horizontal pillars that connect the rails together, sleepers I should say, gosh I hate it when I'm struggling for a word but there you go that was it. Yeah it doesn't, the overhead power lines therefore don't have to carry as much current so they're lighter again they're cheaper so it's having a bit of a resurgence But I want to talk about different methods of pushing trains along either. So there's all sorts of variants like AC traction, DC traction, overhead power, third rail power, maglev, if you're into that sort of thing, or hyperloop, if you're Elon Musk, which is totally crazy, weird, future cool stuff, but that doesn't actually work yet. It's a pipe dream, literally a pipe. Anyway, so there you go. And it's a dream in the pipe. and you just keep dreaming and it might work. Anyway, whatever. As if you can keep a vacuum. Yeah, maybe. Whatever. All right. When they pull it off, Vic, I'll be impressed. Until then, it's just an interesting idea. A pipe dream. Exactly. Anyway, all right. So, sorry, Elon, if you're listening. I doubt that's happening, but there you go. I want to talk about the trade-offs of how rail networks are put together. So quickly, just the terminology thing. What if I say points and switch tracks? You know what I'm talking about? Excellent, cool. So got to change that train from one track to another track. There you go. Okay, so when I say points, you know what I'm talking about. I'm not talking about scoring a game of football or ping pong. What's that? What's that? I don't know. I don't know. Sports. Some sort of sport with a ball. I'm aware of an invention called sports. But that's all I know is that sports is a sport thing with sporting points. Anyhow. All right. All stations versus Express. And Express is in fast on ACC. We're digressing. I am digressing. This episode is becoming a constant digression. There you go. Anyhow. Anyhow. Anyhow. It's off the rails. Sorry, I couldn't resist. Oh my god. All right. You're a legend. Okay. Now, then I'm totally focused. I can't get no focus. That's one for the long term listeners. So, as cities got larger and larger, the trains in the city sort of developed a different set of design challenges. You couldn't just keep adding more and more stations without suffering because the further out you went, the more times the train would have to stop. and that would mean that anyone got on would have to be put through more and more stops in order to get to where they wanted to go, which was in the city. So, when train networks are small, you know, they start with a handful of stations and the train stops at every one. But then the gaps between the stations might be maybe two or three miles or kilometers apart, let's say. Suddenly, there's a new development of housing or a re-urbanization or a green space that gets bulldozed by some jerk to make way for more houses. Yeah, I know. Then you add more train stations in between the original train stations, or you add a few more at the end of the line and anyone commuting from one end to the other now has to slow down, stop, wait for people to get on and off, get moving again at every single station in between. So, it's time to think about express trains and that kind of solve some of the problems, sort of, because then There's different ways of dealing with express trains. So, the idea is you nominate either major or minor stations and you can run two or three classes of train, stopping all stations, stopping major stations or skipping sections of stations. So, the original train lines, the problem is that they weren't designed for express travel. They weren't designed for high maximum speeds through the train stations. and it takes time to accelerate to maximum speeds. So in order to accommodate express trains, they often had to do an upgrade to the train lines to make them smoother, straighter, flatter, upgrade the points so that you could travel through the points at higher speeds so that the trains could basically realize the advantages or the full advantages of being an express train. So because if you didn't do that, then the benefits of being an express really wouldn't be fully realized. But there's a problem with single tracks, because a single track can carry one train in one section at one time. And in the past, railway companies on tight budget might install a single train line between all of the stations, but then the route gets too long. And once the frequency of the trains increases and the route is so long, it gets to a point at which a train physically has to travel from one end to the other and back again in less time than passengers are prepared to wait for that train to come back. So, what do you do? Well, you add a second train, one heading inbound and one heading outbound. So, to accommodate that, you need to nominate a place along the route to have a split in the line where one train pulls over to let the other one pass and then it can carry on its merry way again. Now, in a suburban network, you do that at a train station because that's usually, you know, you've got more real estate to work with. But that unfortunately creates an interlock in the timetables. So, the inbound has to sit and wait for the outbound to arrive at the changeover point before they can continue. And what happens if the train breaks down or it's late or there's a problem with the points? So- Everybody's sitting. Everybody's very, very pissy. They're not happy. So, what do you do? You add redundancy. So we've now reached the point where the train networks look at installing two train tracks, one for inbound trains and one for outbound trains. Suddenly... Just parallel the whole way. Yeah, exactly. And this leads to a dual platform configuration. So, of course, originally you'd have single train tracks, single platform, and that platform would handle both directions. But now you've got inbound and outbound. So now one train platform is predominantly for inbound trains, the other is for outbound trains. So the dual platform configuration than a train station is becomes the standard now. We're going to put crossover points at key places, usually the entrances and the exits of each of the train stations, sometimes between the train stations, and that allows the trains to jump from one line to the other if there's issues. And then of course, we have redundancy in the system. And we have much better timetables with fewer interlocks in them. And you might think, done, you know, wipe the hands, we've solved the problem. But you haven't, because you still have a problem with express trains. See, in order to run an inbound express train, you need to clear the track in front of it, because if every train runs at a constant speed, then we have to use the inbound track only because there's other trains going outbound and they have to meet their own timetable requirements. So as we set two trains running, train A leaves first, but it's an all station's train and it departs at the outermost station at 6am. It takes 20 minutes to reach the fifth station along the line. Train B is an express train. It departs the outermost station 10 minutes after the first train does. But because it's travelling express, it only takes 10 minutes to reach that fifth station because it didn't have to stop. And suddenly, train B crashes into the back of train A. Whoops. Yeah, that's not cool. Yeah, it's totally not cool, man. The passengers are going to be extra pissy. So, and hopefully not dead. So, in order to run express trains on dual track routes, your only option is to clear the lane. Clear the lane. Clear the lane. I meant clear the line. Clear the lane. Yeah, that was a song. Who sang that? Yeah, clear the lane. That was Rage Against the Machine. God, that was a weird song, that. Hmm. Okay, that was a real... Anyway. You're off the rails again. Gone Off The Rails, again, about an episode about trains, so typical of me. So, the thing is, you could jump between the inbound and the outbound, essentially, you could dodge the all stations trains heading the other direction, heading the same direction and dodge the trains heading in the other direction. But if there's any congestion anywhere on the outbound leg, you're screwed. So, you know, whoops. So, as the networks grow and the demand for express trains increases, you have no option but to add yet another train line that's specifically intended for express trains only Some people call it a bypass, it doesn't have a train platform Sometimes they do have train platforms, sometimes they just go and bypass the entire train station So if you're on that express line, then you never stop at that station ever, no matter what Anyhow, irrespective of that, in that situation where you now have three tracks one inbound, one outbound and one for express. Because your express trains typically follow based on the time of day. So, the morning rush, you have express running in and evening rush, you got express running outbound. Then they'll often run that third train line as a tidal flow system. That is to say, you know, the direction that you have expresses changes based on the AM or PM. So, that's an interesting way of managing that travel corridor and still getting most of the benefits. But the final expansion of your train lines comes when you start running express trains in both directions at the same time as all stations trains in both directions at the same time. And that inevitably leaves you with one conclusion. You need a fourth train line to cover that circumstance. And that's how you end up with the four train line configuration. Making sense so far? Cool. So, Star vs. Loop. This is another one that's made me think a lot over the years. So, there's a conundrum faced by cities everywhere in the world because there's always a central focal point where it all started. And it's sometimes referred to as the CBD, the Central Business District, or more simply, downtown, you know. Or hang on, more recently, it's like 800 cash, that's a hell of a deal, if you know that song. No? I think I may have heard it. Yeah, so what's up, what's your budget? Anyway, this leads to the urban sprawl and lots of jobs, and I'm not going to take up wrapping. I swear I will not, at least not on this podcast. Located in the city centre, meaning all the trains lead to the city, just like all roads lead to Rome, all of our train lines lead into the city centre, because that's where you want to go. You want to go downtown, and I'm going to stop there. This causes network design to resemble a star pattern. Of course, you may have to use your imagination. Of course, you could also think it looks a bit like a ninja star too, but again, use imagination and potentially some kind of psychedelic compound. But it looks a bit like that. So, actually no kids don't use psychedelic compounds. In Brisbane though for example every single train in the entire network must travel through four stations. Roma Street Station, Central Station, Fortitude Valley Station which when I was of course younger was referred to as Brunswick Street. Why did they have to change to Fortitude Valley? I don't know. Anyway and then finally Bowen Hill Station. There are no ifs, no buts, no alternatives. You have to go through those four stations except there is one bypass line just one and that they call the exhibition loop but it causes the train to turn around the wrong direction into Roma Street so if you're coming south there's no way to get to the other stations unless you swing around heading north and go through the wrong way around well not the wrong way around physically but you know back to front in terms of sequence and there's only one line so that that doesn't work out so good. So, if there's a problem at any of those four stations that I just mentioned, the ripple effect is enormous. The entire network grinds to a halt and believe me, it really does. It totally does. It's just unbelievably bad. So, some bright person many, many years ago, because of course, Brisbane's architecture is not unique, it's very common. They came up with this idea of a ring or a loop. And in road parlance, we would call it a ring road, freeway parlance, I guess you'd say. Or in railway parlance, we'd call it a rail loop. Rail loop, ring road, same idea. Okay. So, the idea is that not everyone wants to travel into the city, as in the city isn't their final destination. So, let's say maybe 80%, I don't know, pick a number, varies from city to city, but the vast majority do. But what about all the people that don't? People are forced to travel through the city and out the other side again to get to their final destination. What if we designed a loop that allowed people to skirt around the edges and bypass the inner city completely? It's even more justifiable if you're in a bigger city like Sydney, when you got several distributed, non-city city centers like Parramatta, Liverpool, Campbeltown, that sort of thing. And of course, I would if I was more familiar with, you know, like Manhattan or something, I could probably give better examples from North America perspective. But alas, anyway, it doesn't literally have to be a single train that goes around, around, around, around and then it'll sloop. It doesn't have to be it just means that you could take one or more trains between two different stations and never go near the city center, which is the whole point and that takes load off of that city centre. Right now, most frustratingly, Brisbane does not have a loop. Shame on you, Brisbane. Fine. I'm sorry, John. I know. I'm sorry, too. Guess I'll just have to move or stop taking the train. That's the other option. Sprawl versus speed. So the other thing to throw on the ring relates more to how the design philosophy of the train tracks has shifted from the old days as then as to now. So, back in the bad old days, if there was a house or a farm or a creek or a fjord, some other kind of natural barrier of some kind, you know, some immovable object or difficult to move object, the train line would just go around it. And if the train trip took an extra five minutes, then, oh, well, too bad, so sad, suck it up, passengers ride, it's a train and trains are cool. Choo-choo, chugga-chugga, whatever. But that's the way it used to be, right? It's like people weren't in- Choo-choo, chugga-chugga. Choo-choo, chugga-chugga. I mean, you weren't- They weren't in as much of a hurry, you know, but as a result, the trains tended to get a reputation for being a slower means of transportation because, you know, aeroplanes and, you know, freeways and so on. But when all that happened, that then put pressure back on the trains, like, okay, well, what if we didn't have to go around that farm or we didn't have to go around that mountain and that resurgence that you could have an incredibly fast train that started to happen. It was led, I think, the pinnacle of it was the TGV in France. And there's one thing about high-speed trains that a lot of people don't understand, and it's all well and good to have common bogies connecting carriages, having streamlined, low drag coefficient, pointy nose train things that punch holes in the air, blah, blah, blah. But you know what? It's useless, completely useless without a straight, flat, smooth train line. If you try and make a train going 500 kilometers an hour, go around a right hand bend that's got a 60 kph speed limit, well, you're going to fly off those tracks pretty convincingly. So you have to have a straight, level, flat track that is smooth as silk in order to go those sorts of crazy speeds in a train. So, the new condition that railway line engineers now have to optimize just got changed, the goal posts just changed. No longer is it about getting people between point A and point B for minimal cost. Now, everyone looks at time because time is money. We get them between those two places as quickly as possible. More importantly, quicker than driving, quicker than taking the bus. Mind you, if you're taking a personal Learjet into work, good for you, or a helicopter. Again, good for you. That's nice. So, you know, for normal people, the train has to be quicker. Now, but that has to be quicker than alternative means of transportation. Otherwise, there's no incentive to use it other than cost. And even then, sometimes it's not cheaper. So, the train line, as an example, near my place between Caboolture and Beerburrum, that was upgraded about six years ago from being single track. Cannot believe that was a single track for the longest time. It was, I think, the busiest single train line in Australia and had been for a long, long time. Well, they finally upgraded it to a three line system. They built new bridges. They bought a huge strip of a strawberry farm because where I live, I've got a macadamia farm down the road. I've got strawberry farms, pineapple farms. Really is a nice area if you do that sort of stuff. So, yeah, kids love it anyway. But what they did is they just punched a massive hole through a hill just to make the train line straight, flat and increase the top speed to 140 K's an hour. And that cut two minutes of the traveling time just between Caboolture and Elimba and then from Elimba to Birbaram again, another two minutes, just by straightening the line, you know, because the original line had a series of tight, sweeping curves and it avoided the hills and the houses and the farms. But that was then and this is now. And now we feel the need, the need for speed. That sounded more disturbing when I said it out loud than it was in my head. Sorry. Anyway, it was a little disturbing. I think that's about enough about networks and stuff, hey. So, signaling. Want to talk about some signaling now, Vic? Sure. That was the point at which you're supposed to say stop. Okay, stop. Because that's a signal, because the stop is a signal and it's okay, it's fine, it's fine. You nailed it with the going off the rails before, though. It's okay. So, I should go. It's late for me. Okay, signalling. So, for trains, again, I'll just reiterate, takes a long time to stop. You can't always see what's coming and you're traveling fast in many cases. So, the methods that we use for cars, trams and light rail just won't work safely enough. So, trains, heavy rail trains I'm talking about now from now on, trains today generally employ what's referred to as an occupancy or block based system and we'll use different forms of signaling. the most common acronym that I've seen used is MAS, which is Multiple Aspect Signaling or Multi-Aspect Signaling, MAS. So train traffic lights, they look like normal road traffic lights in some cases, sometimes referred to as train signals or traffic signals, I guess, but they operate on a fundamentally different philosophy to traffic lights do for cars on the road. So traffic lights on roads, they're based on the idea of flow control, whereas signals on train networks are based on occupancy control. And understand why they're different is the problem with everything. Okay, I got to state this up front before I go any further. Everything from here on, there is a lot of variation between different states in the same country, between different countries around the world. It is absolutely impossible for me to draw to describe them all and to be complete about it. In fact, some of the things I'm about to say, you may say, "Well, that's different for our train network in our country." And you're damn right, it probably is. But I guess my problem is that I've done a lot of research into this, I've been to different countries and I've paid attention to the different signaling methods that are used. And I'm going to try and keep this as generic as I can, whilst at the same time covering as many of the most common options as possible. So with that said, let's keep going. Essentially, signaling is going to fall to two broad types. You got mechanical signaling and you got colored signaling. And of these, they broadly indicate two classes of indications. You've got point positions, as in switch track positions, and block occupancy of the train's intended path. And that intended path is important, as we'll get to later. So, mechanical signals first. Semaphore, like Navy semaphore with the flags. The guys with the flags. That's it, man. But mechanical flags, like, they vary from country to country, but they're usually like a combination of white, red or black, because that's high contrast. And they're usually rectangular arms and they have a pivot point at the pole where they came to the pole. They sit high on a pole beside the railway line, usually adjacent to the points or just before or after a station where there's a logical break in the blocks because they'll break the track up into a series of blocks, then the blocks could be, you know, like a mile or two long. And that's where these things sit. Now, before electric and remote point switches were a thing, they were physically mechanically coupled by linkages, like a mechanical solid steel bar linkage to the point mechanism. So when you would lift and turn the point control arm, the angle of the semaphore and the mechanical signal would change. Now, the standards vary around the world obviously, but directly out horizontally almost always means stop. Directly upwards isn't always used, but where it is used it almost always means proceed. If it's tilted up or down at an angle, it usually means proceed with caution or simply just proceed. So, coloured signals for block occupancy, unfortunately, vary a lot. But where you see coloured signals, red, is almost always used to mean stop, as in, there is a train occupying the next section of railway track, so it's not safe to proceed. After that, there's pretty much nothing in common. So what I'll do is I'll just talk about the mass multi-aspect signalling used locally here in Brisbane, for example, as an example of one way of doing it. So, they predominantly used four aspect signals, one red, one green and two yellow indicator lights for the traffic light. So, it looks like a traffic light and some idiot put a second yellow light, a second amber light on there. They're like, oops, hey, we have a spare yellow light, we'll just put on here. So, the idea is each of the lights indicates which block or series of blocks is occupied. So, red means that the next block is occupied. Do not enter. So, there's a train currently on that block. So, the next train comes up that light. It's like, oops, can't go anymore because there's a train on that block. Okay, stopping now. One yellow light means that the next block is clear, but the block immediately after that is occupied by a train. So, you could go, but go with caution, because if you go too fast and you get to the next block, you're just going to hit a red light probably. Two yellows means that the next two blocks are clear, but the block immediately after those two is occupied by a train. And then finally, green means that the next three blocks consecutively are clear of trains. So that's just an example of how they've done it here in Brisbane. And that's all nice and swell for Brisbane. But hey, everywhere else is different. So because there's no real standard because who needs a standard, right? You know, like crazy, tiny railways. Anyway. So point positions, they're usually little clusters of lights. But you can also have mechanical indicators. So mechanical indicators usually it'll be like a black circle with a white bar usually as a diagonal. It's either well, I guess it's either level or it's at an angle and the angle could indicate which side the point is connected. Pointing downwards may indicate that the point is switched to the right, angled downwards to the left might say the point is switched to the left. It depends on the position of the signal, the position of the points and the country or the state you're in. Using lights, they'll have usually like an inverted T, so it'll be like four lights. So it'll be three in a row on the bottom with one above the middle light forming an inverted T-shape. That's quite common and which lights are on. So it'll be like the two center lights always be on and the light on the left or the right will indicate the point direction either to the right or the left. Some systems actually use a series of three or four smaller lights and they go at an upward angle directly above the main traffic lights. and some people refer to that as a feather or at least in Queensland, they call them feathers and that'll essentially then informs you about the point position it also informs you about the condition of the light so the condition of the lights, let's say you've got a red light and the points are switched straight ahead it means that the block directly in front of you straight ahead and the points is occupied, so don't proceed but if the feather is lit and the feather is off to the right It's telling you your points are now pointing to the right, and that could be green because it means that if the train goes to the points to the right, it's on a different track and that track is clear for three blocks ahead of you. So, the lights... Okay. Yeah, so the lights indicate the path the train's about to take is clear. Anyway, so that's just... This is all a lot more complicated than I ever realised. I know and the worst part is that there's no standard for all of this stuff I think most of us just think train go down track Yeah, it's like get on- See, this is the problem now people know what I mean, they probably already know that I'm a bit different, but that's okay. I sit on a train and I can't get to where I want to be and I sit here and I think about why am I stuck here and I shove my head out the window and looking at the train and the lights and it just got me thinking 20 years ago, I'm sitting on the train watching the lights and I'm like, why are there four lights here? And so I talked to a few people, learned a little bit of stuff there. All of those notes that I put together, five pages of notes that went into this episode, most of that I wrote from memory because I've been on trains for so long, I've been thinking about it for so long. I find it fascinating the way that trains have evolved, the way that train networks have evolved, the signalling methods that they use, because flow control at a traffic light, it's about timing. Yeah, so it's the cars go forward, you have a predominant flow direction and you'll run the lights on a timer and the timer says you can have two minutes of forward flow in your traffic. Once the two minutes are up, go red, that's it, then give the other direction to go. That's flow based signaling, you get intelligent traffic lights that talk to each other. And they also say, well, give me an extra 30 seconds to clear this bank of traffic, you know, so they might dynamically extend the timer. And then you'll have other ones that operate in after hours like alternating trigger mode. So you'll alternate between traffic moving in one direction and then traffic coming from the side street. So you'll pull up to the lights in the side street. The predominant flow of traffic will continue indefinitely until it's interrupted by someone pulling in a side street. Yes, that sort of signaling is completely different to an occupancy-based system, which is what trains have to do, the heavy trains have to do. So pretty cool. It is. There's a lot more to it than I ever realized. Yeah. For all those people out there that just get on a train, go from A to B and smile and are happy. Yeah. There's a part of me that kind of is envious because I just can't do that. That's OK. Yeah. Any other thoughts or comments you want to make? Because I'm at the end of my notes and I think that I could go on a lot more about trains and like I'd start talking about more like rolling stock now and I guess, but I don't know, I don't find that quite as interesting. And when I finished my degree, I thought about going to work for Queensland Rail, but it was a brief thought. And I know people that are still there. Mine, I'm coming up to two decades now of engineering. It'll be later this year, I will have done 20 years of engineering. And it's funny, you know, because you see people on LinkedIn and it's like coming up to my 20th working anniversary at Queensland Rail and I'm like, oh my God, really? They left uni, they went to work for QR and they never left. And I'm like, I don't get that. I just get stir crazy. I got to go and try a different company. My longest stint at a company was six and a half years. And you know, I just I get itchy feet. I want to learn something new, do something different, you know, I just I need to learn more. I can't just be idle and continue to grind through the same old stuff. It's like, oh, what are you doing today? Oh, we're going to have a look at the same train line we've looked at for the last 20 years and we're going to put in some more ballast. Might be like, kill me now. I just couldn't do it. Kill me now. I just couldn't. I'd be like, come on, man. Can we put in some maglev and like, nope, no maglev for you. Get out. Don't belong here. Can we do a high speed TGV? Nope. Can we straighten that? Nope. Can we, can we? Nope. If you want to talk more about this, you can reach me on Twitter @johnchiji or you can follow Pragmatic Show to specifically see show announcements and other related stuff. Remember that pragmatic is now part of the engineered network and it also has an account on twitter at engineered Underscore net that also has show announcements about the network and all of the shows so you can check that out at engineered network If you'd like people are really loving causality and nutrium as well So if you'd like pragmatic be sure to check those out if you'd like to get in touch with Vic What's the best way for people to get in touch with you mate? They can find me on twitter at Vic Hudson one fantastic and if you're enjoying pragmatic and you want to support the show the best way is by becoming a patron via patreon it's at or one word and If you'd like to contribute something anything at all, it's all greatly appreciated There's also a few perks in there If you'd like to access the raw show notes and show backers can have a named Thank you if they want at the end of each episode So check it out as I said it all helps and it's all very much appreciated Thank you everyone for listening once again and as always thanks Vic. Thank you John pleasure Take care. [MUSIC] (upbeat music) (upbeat music) (upbeat music) (upbeat music) (upbeat music) (upbeat music) (upbeat music) (upbeat music) (upbeat music) (upbeat music) ♪ ♪ (Music plays) That's good water. Because if I have coffee now, it's ten past eleven. That would be a bad play. Hey, you'd be up all night. This is all night. This is me up all night talking trains. All right. I just did a metal symbol with my fingers there. Would that be the devil horns? Yes, it would. I'm thinking I'm channeling Craig Federici just now. Anyway, I'll never get that image out of my head when he wanders onto the stage at, I think it was WWDC and he says, "And we're going to call it Metal." He does the fingers thing. Yeah, that was a good one. Craig Federico will forever be cool in my heart because of that one moment. I don't care about the gags about his damn hair. That one moment is all I need.
Duration 49 minutes and 7 seconds Direct Download

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Vic Hudson

Vic Hudson

Vic is the host of the App Story Podcast and is the developer behind Money Pilot for iOS.

John Chidgey

John Chidgey

John is an Electrical, Instrumentation and Control Systems Engineer, software developer, podcaster, vocal actor and runs TechDistortion and the Engineered Network. John is a Chartered Professional Engineer in both Electrical Engineering and Information, Telecommunications and Electronics Engineering (ITEE) and a semi-regular conference speaker.

John has produced and appeared on many podcasts including Pragmatic and Causality and is available for hire for Vocal Acting or advertising. He has experience and interest in HMI Design, Alarm Management, Cyber-security and Root Cause Analysis.

Described as the David Attenborough of disasters, and a Dreamy Narrator with Great Pipes by the Podfather Adam Curry.

You can find him on the Fediverse and on Twitter.