How Railroad Crossing Signals Work

someone else. That was such a terrible stretch. But you know what, I'm gonna save myself here by going into a little listener mail. This listener mail comes from Weston, who says, Hi, my name is Weston. Well I know Weston. I just said that I'm from South Carolina and looking through your white extensive list of podcasts, I could not

find one that involved how railroad crossing signals work. So I was wondering if you could explain that, and if you could explain how railroad crossing systems tie into traffic signals in more urban districts. Thanks a lot, keep doing your thing. Well, thanks Weston. Yes it is true. We had not done a podcast on railroad crossing signals. Uh, it just never honestly occurred to me, and in fact, until I started researching this, I had no idea how

complicated it really was. That's true, although they have changed over the years too to some degree. Yeah, it used to be that the railroad crossing signal was that the train in very busy areas, the train would come to a stop. A flag man would go to the crossing area and and manually stop traffic for the train to pass through, and then would go jog get back on the train and then everything would start up again. So

that's about you know, that's pretty simple technology. Yeah, have to agree that that's uh well, there's not a lot of electronic technology involved in that. At night, sometimes they'd use flares. I've actually seen that. I've there was a rural crossing, a railroad crossing in northern Georgia, which is where I grew up. What you can tell because of my deep Southern accent, But in in rural Georgia there

was a crossing at one point. I remember as a kid we came up to it, and I think the reason for using the flares was not because there was no modern crossing signal there. I think the modern crossing signal was unfortunately out of order, and so they were using the flares as a backup system and UH, and that's exactly what they did. They stopped the train, a guy got out and lit some flares along the side of the tracks, and then the train went through and we had to wait, and then we drove on by.

Well then it actually seems like it could be a little bit more reliable than some of the technology that we we're researching. UM. I have to have to give any shout out actually to uh matt Enus who has a really awesome website about the electronics behind railroad crossing signal technology and it's it's very very through. Apparently he really likes electronics and trains, so this was sort of a natural for him. Yeah, you can find his his website at Matt dot z o n T dot org.

I thought i'd give a shout out because I also found it really helpful. He has lots of of of technical drawings for for circuitry as well as some great animations. It really makes understanding this UH a lot easier, although again it's still a very when you get if you really dig down, it's still really complicated. Well A said it. As it turns out, just about every type of signal UH crossing signal uses some form of an electronic relay

or I should say electrical relay. Um. And a lot of it has to do with basically detecting that a train is coming. Now it's not necessarily from a distance. In a lot of cases, it's basically when it's right on top of the crossing, not literally right now, when when it's right there at the crossing before it gets to the uh for it actually gets to the intersection

with a roadway. Yeah. Yeah, so there are some there are lots of different types of these these systems, we should say, because first of all, uh, it's it's easy to forget that the railroad system is not a unified

thing overseen by a single entity. No, that's correct. There are several railroad systems throughout the United States alone, and you know that's just the United States where you know, it gets way more complicated when you're looking at things like international railroad systems that go through most of Europe

for example. UM. So, because there are all these different entities that are running the railroads, I mean there are are certain standards, like railroads are railroad rails are at a standard with where else your trains cannot go from one system to another. But things like the signaling systems the electronics they use are not necessarily standard across the board. They're all supposed to operate in a standard way, but the way you get there is not necessarily standard. If

that makes sense. Well, what I thought we might do is actually talk about the signals themselves, and then we could talk about the way that they're triggered me because um, you know, and at a given intersection. Actually, that's that's another good point back to what you just said, was um that not every signal, uh, not every crossing has the same types of signals either, even on the same uh, even on the same railroad. So you know a lot of times you'll see you know, the signal mast, which

is that poll with the lights on either side of it. Hum. And basically this is just a current flowing through, just like you would with a typical light bulb. Um, but it's it's got a relay, a flasher relay between that basically alternates the circuits. So one light goes on the other one goes off. Then they switch back and forth,

back and forth. Yeah, I think it pretty easy. Think of the flasher relay is kind of like a switch that opens and closes, but when it when it when it opens for one side, it's closed for the other and vice versa. So as long as power is running through this, one side of the lights will light up and the other side will remain dark. And it alternates, and that's what creates the flashing pattern. And they alternated.

There's one way that it can be alternated. Again. There are lots of systems, but one way that they can alternate is through using electromagnets. Our old friend, the electromagnets, right, So the electro magnets will have a set of coils on either side, and when one set of coils gets power, that pulls the switch to that side and creates a magnetic field which pulls the switch her. That's what lights up the lights on one side, and then the other

set of coils will get power. The first set will lose power, so now the switch will be pulled back to the other side, which will light up the other side of the lights. And alternating this back and forth is what gives you that click click click click as the as the flashers go on and off. Uh. I will have to say, though, that this behavior changes dramatically if you happen to be within a certain distance of UFOs, as seen in the documentary but nothing but Close Encounters

of the Third Kind? Man, did you not watch it? I mean those lights went crazy. This means something, This is important. Okay, that was That was clearly a joke. I was referencing a Spielberg movie, Close Encounters of the Third Kind. I do not, in fact believe that aliens affect our railroad crossings at some too busy messine with our fast food restaurants. At some point we should uh do a podcast on why every time aliens come down your radio dial changes and the rail road You're always

near a railroad. You know what drives me stuff podcast? I'm listening to the radio and next thing, you know, aliens come down and it switches the golden oldies. I just hate that. Um And we got a little off track on our railroad podcast speaking speaking of electromagnets, so that the same the same uh things sort of applies to the bell. The bell that goes clian client client clang, that tells you that's going on, except, um, what's going on there is the electromagnet is pushing the clapper to

the bell. The clapper is the thing. If you're not familiar with bell technology, and I'm not talking about mob bell, it's got the il communication. Um, you got the clapper being pushed to the side of the bell by an electromagnet. But the thing is the thing. I thought it was cool about this at least according to to Matt's page. Is what happens is once the clapper reaches the bell, it's breaking the connection uh to the electrone, so it pulls it back and it pushes it back again. So

it's just snapping back and forth. It's the momentum that carries it forward so that it actually makes contact with the bell. Yes, and then it gets pulled back to its original position where again where and then it gets pushed again. Yeah and yeah, that's kind of that's pretty neat. And of course it's happening at a regular interval because of the the length I guess of the piece, the

physical clapper piece. It's it's a centrical same same principle that you'll find on other alarm bells, things like you know the classic fire station alarm bell works on the same principle. I'm sorry that kind of alarms me. Yeah, well I live right next to a fire station, so really familiar with the fire station bell. Okay. So the gates that drop down in front of the uh the crossing, you know, the red and white bars basically if that, sometimes have lights on them. Sometimes I don't. UM, they

use a different kind of technology. They actually use a motor UM and there's a relay called the motor control relay that basically allows the the motor to operate in one direction as the gate comes down. So basically it is starting to push the gate down and at a certain point, of course, you know, there's a weight on the other end to counterbalance and um, at a certain point the gate would come crashing down, so about midway down or so, the relay switches the motor to prevent

it from the gate from crashing down too quickly. So on what you know, at the beginning, it's starting it down and then the bottom is like oh okay, okay, okay, not too fast, not too fast, all right, there you go. So yeah, so in one case it's actually pushing it downward, and in the other case, it's pushing upward, but not so hard that it makes the gate go right back up again, right, and just slows the gates decent. Yeah. And and of course there are many ways to achieve

this effect. Apparently it has to do with the manufacturer of the gear. Um, at least according to Matt, it's really useful railroad signal technology page. Yeah. And and the reason you don't want those gates coming down too quickly, I mean, apart from the fact that it's gonna cause way too much wear and tear in your equipment, is that you don't want to whack cars that are in the the the railroad area when the signal is activated. You know, you have to have enough time for the

car to clear. Um. That's also that's really the chief reason for the bell. The bell is really there to let people know people who are on the tracks at that moment as they're crossing over, that hey, there's a train in coming, your best get some moving. But that they use the bell ringing noise because they found that having an old guy send and they're yelling that out just wasn't nearly as effective. Yeah. Yeah, it's um one of those things that people still try to circumvent quite

frequently terrible, terrible idea. It's a very very bad idea to try to drive around the gates um or you know, if you have to be any crossing, like there is one near my house, Um, people often go through and sit there on the track waiting for the light change. And that's just a bad idea. Yeah, you don't want to be there. There are stories I could tell, but I won't, but yeah, it's just a bad idea. So that got that. That covers the UH the basics of the arms and the mast, yeah, and the lights that

in the so and the these this system. By the way, you asked Weston specifically about how that works within urban areas. The system can be keyed into any adjacent UH traffic signal. Essentially, it's just part of that traffic signals cycle. So if the traffic signal receives UM signal from the railroad crossing its superseds, anything else on that intersection, so instead of the lights cycling through as they normally would, it'll be

stuck on a particular setting. So maybe like the parallel road would still get green, but the road that would intersect would have a red until the until the signal from the railroad crossing gave the all clear. Yes, that's that's exactly how it works. At the crossing near my house. It blocks out all the traffic that would necessarily cross.

And the thing is, I've I've seen cars unfortunately who uh not unfortunately in the other sense we were speaking of earlier, the ones who get there at the red light waiting to cross. There's there are basically two sets of there's two roads, one on either side of the tracks parallel to it, and they'll go and they'll wait on that red light and then the gates will come down. They're going, Ah, you gotta be kidding me. I mean, there's a train coming and now I have to wait

through this. Yeah, this was gonna be maybe a min and a half way, and now I'm looking at upwards of three to ten minutes just fitting on the train. I gotta say, though, I did have that happen to me not that long ago, but it ended up being a thing as opposed to a bad thing, because it was a circus train. It was actually really cool. That's yeah, um Dumbo waved, Okay, Well, actually that's that. This is where it stops being quite so simple to explain, because

those are the signals. But triggering the signals, that's that's a little more more tricky. Let's let's talk in a really high level way, because if you dig down, it just gets to the point where you really need a good I was about, say, grounding a good understanding of electrical engineering in order to uh, to really follow and because probably I would guess most of our audience doesn't have that necessarily. I'm sure there's some of you who do,

but I think the general audience probably doesn't. It would just be it would be torturous for us to try and walk through it. Yeah, I'm not sure that I have the the basics down enough. Sure I don't have the basics down, but we can talk a little bit

about it from a high level. Um that virtually any of the crossings that have electronic signals, you're gonna see one of those boxes like you would see at a at an intersection in an urban environment that has a series of relays and basically a couple of batteries in it. You might say, why does it need the batteries? Well, Um, the tracks around the railroad crossing have a circuit in them that helps control the railroad crossing signals. Yeah, let's to kind of give it a basic set, all right.

Imagine that you have a stretch of railroad track, okay, and that you are approaching You're you're walking along the railroad track, and you're you're gradually getting to a point where the railroad is going to intersect with a road. Now, as you're walking along that track, you will eventually come to a point where there will be a special insulator block that is on each rail. Now, this insulator block, the whole reason for this is to allow there to

be a circuit along a stretch of track. If you didn't have that insulator block there, the the electricity would just flow through the entire track and just disperse essentially because you would have like the world's biggest circuit. So you have to block it off. Yeah, and this is not the kind of charge like you'd see on light rail, um, you know the third rail. Yeah, this is not to provide power to the train at all. No, No, it's just detection system. Yeah exactly. So you've got you've got

these insulators, that's what blocks the electric signal from continuing through. Uh, You've got and you have relays connecting the two tracks together, and you constantly have a low level of power going through this this basic circuit all right. Now, Uh, there's usually another insulator block somewhere near where the actual road intersects, and then you have a second set of circuits on

the other side and in its most basic form. And the reason for that is so that you can detect when the train passes from one one part of the track to another part. And that's important because eventually you're gonna have to have these signals stop signaling. You have to have something that tells the electronics, Hey, the train's gone, turn off the flashers, turn off the bell, and lift

the gates. Yes. He As a matter of fact, the the part of the track approaching an intersection is called the approach yes, which by the way, is not always the same side because trains, because some tracks will allow trains that travel in either direction, So the approach is completely dependent upon the direction the train is coming from at any particular time. So the approach side will change

depending on the where the trains coming from. Um. Now, when a train crosses over the insulator and hits the section of track where you've got that circuit, the trains wheels are steel. The axle connecting the wheels are steel.

This massive amount of steel when it makes contact with the tracks creates a short circuit, which means that it's it's it's pulling the power, so it's no longer going through the relay like it normally what it's going through the axle instead, and that's what is That's what creates the the alert for the signaling system that hey, there's a train coming. Now. There are other problems with this, yes, one of the big ones is that this does not tell we're acting like this is all like you know,

they're all coherent and cognitive. It's not. But this does not indicate how fast that train is moving, just that there is a short circuit, and therefore the signal should go off right. So you have a couple of different things you have to take into consideration there. One is, are all the trains that are traveling on this track

generally going to be moving at the same speed. If they are, that makes this problem way easier to solve, because what the problem is you need to figure out how long from the moment that this short circuit happens,

should the signals. What's the time delay between when the short circuit happens and when the signals activate, right, because if the train is too far back and the signals activate, you you take everybody off because they're like, well, look, the gate came down and I've been waiting here for for fifteen seconds and I still don't see a train.

I'm just gonna go, and that's going to cause a problem. Um. In other cases, you may have a train this moving so quickly that when it triggers the short circuit, it actually reaches the intersection before the signals go off, so

you have to take that into account. Now, if all the trains are moving at the same speed, you just figure the right distance from the crossing and you install everything that way, and then there's no problem relatively speaking, because the trains are always going to hit the intersection at around the same time, so you can time it out that way. If the trains are gonna be moving at different speeds, then you have to figure out, okay, well, how do I indicate how fast this train is going.

You can either fudget where you kind of take an average speed of all the trains that tend to go across that track, or you can pick the trains that are the most common, like the ones that are are usually on that track or that travel through there during high traffic areas and use that speed. Or you can install sensors that actually do indicate you know how fast the train is going and then send that information to the control system to alert it when it should initiate

the warning. So those are your various options. But yeah, that's it's all about short circuiting, which is kind of cool because when you think about it, you know, the connotation of the term short circuit has usually a fairly negative feel to it, right, you know, you know, you normally don't want things to short circuit unless you're Johnny five nice. Yeah, I like that. I figured I had to work that in there. Well, he was alive, he was theoretically, Um, So the thing is you have so

that that's basically how it knows it's coming. The question is how the crossing signal UH is notified when the train is gone. And so basically there are are two sets of tracks there too, since there are two approaches, because theoretically, if a train could come from either direction, you would want that anyway, but you also need the

other approach to to notify it too. Because um, as the train passes from one side of the crossing to the other, there is another uh, there's another circuit too short.

And when both sets of circuits are therefore untriggered anymore, that means, well, the train has come and gone, and those signals can you know, the the arms go back up and the lights go back off, and the bell stops clanging most of the time, but there are problems with it it you know, those of you who live near railroad tracks and have seen trains do this annoying behavior. Um because of course they probably have to. There are

reasons why they have to. But for the driver it's kind of annoying to sit there and watch a train stop and then back up a little bit, and you're going, how long do I have to wait? Well, that does happen from time to time. They're there, you know, traffic issues to be considered. And the thing is the relays

aren't exactly endowed with a lot of artificial intelligence. They they're either on or they're off right, And there are times when a track, a train can pass through an intersection and then it has to back up for traffic reasons a little bit, and that triggers the signal again, and then when it leaves, it's you know, there, there's it can it can trip the signal to a point where the next train that comes from from uh, you know, I'm not sure if it comes from that direction from

where the train left, but it may not necessarily trip the signal because of the way it's wired. So what you're saying is that that because the train activated the signal the first time, then reactivated it without crossing over into the opposite side. Uh, you've got a faulty system. That's how I would have said it if I were more eloquent. Well, like I had the opportunity to really think about it and listen to what you were saying. So that was that was It's not that I'm it's

not that I'm pithy or anything. I just had more time. Um. Yeah, there is a problem. There are some ways around that. One is to create a kind of a failsafe system where you add a third set of a third circuit two circuit system, because remember we've got we've got the side that the trains coming from and the side that the train is going to. Uh, and usually that that ends up having a break right at where the cross is um and when usually normal in normal operation, as

one side gets activated and the other side becomes unactivated. Uh. You that that's when it says, okay, well the train has passed from this one side, we can now raise the gates and turn off the lights and all this

kind of stuff. If you add a third section that's directly over where the road crosses over, uh, and then you you create that that can give you that extra set of circuits there that will allow you to either switch something off if the train does have to stop and back up, or more importantly, I think there is the chance that let's say the train has passed over the the first the approach. Okay, so the end of the train has left the approach, there's no longer any

contact there where it will create a short circuit. But the train has not left the other side yet, It hasn't gone through, and then it starts to back up. You may have gotten to the point where the warning systems have shut off and the gates have gone up,

but the train is still approaching that intersection. Right. That's also dangerous because everyone thinks, oh, I can go through now because the gates went up, the lights are off, the bell is no longer ringing, but it's because that the the full circuit hasn't been tripped yet, so the train starts backing up and you are possibly endangered. Adding this third circuit, where you have a section of track in the center between the approach and the departure area,

allows you to create a fail safe. So some crossings do have this, some don't. It all depends on when it was built and the last time that it was fixed really adjusted. It's called an island, yes, the section that is directly over the road, and apparently it does

have there. There are some certain reasons why you want it to be an island that goes over both sides, because if you have the insulators or anything like that built into the road itself, the thickness that the road can actually affect the way the signal is tripped, so you really have to uh really have to leave the

rails that crossed the road. I thought that was kind of interesting actually, because I was I was thinking as I started reading um reading up on it, I thought, you know, when I go home, I'm gonna look and see where the the insulators are that that split the two approaches. And then as I started reading about it, you know, it dawned to me. Yes, I mean, if they have to repave the road or something like that,

it's going to affect that. And if the train rolls over um that and can't actually you know, it could actually be a problem. Um. But that that is one way of doing it. And then there there are other pieces of equipment that can be added to refine the

capabilities of the signaling equipment. For one thing, there at a really you know, nice new modern crossing, you might have a lot of solid state electronics and you avoid all these these circuit relays and stuff and you just you use solid state instead, which it works kind of on the same principle, except that there are a lot fewer parts. You know, it sends a lot of electronic signals directly to the the traffic control system for that particular crossing. But but I mean, you know that's it's

not by any means a universal thing. It's it's all regional. And you know, some areas are going to get that equipment much faster than others, and some may never get it. Frankly. Yeah, yeah, now, Now, Mattiness also said that there are some signals that use transceivers built into the boxes that that help identify how

quickly the train is moving. Um. Basically by measuring the voltage um, you know, and judging by the impedance of the wheels on the train moving, it can kind of tell as the voltage drops how quickly the train is going to approach the intersection, and can drop the signals at a more appropriate time. UM. But you definitely want to make yeah, yeah, English major fair enough. Um. But there are also some of the newer intersections also use

motion detectors, which which can help identify these things. But in essence, that's that's what it's doing. It's just basically looking for information from the rails themselvesselves in a lot of cases. UM. And I think it's it's probably uh trickier because in urban environments simply because you have uh, you know, more intersections to worry about, and you also

have more car traffic. And like in the case of of the intersection near my house, you've got two roads parallel, so you've got two traffic lights to deal with at that railroad crossing because the piece of road crosses too uh car intersections you know, within my guests probably uh hundred feet of one another. So it's a very short section of where there are two intersections right on the other side of the railroad College avenues that way. So yeah,

that's uh College Avenue in Decab Avenue. Yeah, yeah, that's true that those are from my Atlanta peeps. Yea. So it's just one of those situations where you just got a lot to be concerned with. And I imagine that as time wears on, these uh, these roadways and railways will be updated with more solid state technology that will give you a better idea of what's going on and when. Um. But you know that the the systems that they've had have been somewhat uh, somewhat elegant, I think in their design.

I mean they're just they're simple, and I think sometimes that can be for the best. Yeah, uh, keeping keeping it simple stupid is always a good uh philosophy to follow. And and we should add that the railroad signals. Of course we're just talking about the crossing ones. There are there are lots more signals that that railroad companies use

to manage traffic on the rails. And it seems like it might you know, for at first blush, you do think, well, how how tricky could it be, but then you think, wait a minute, this is a dedicated pathway that only one vehicle can travel in a direction at in a particular area at a time. So it does get really complicated when you think, oh, well, how many trains are on the system. How many systems are we talking about?

Because the rules from system to system change a little bit, you know, like the rules in the Northeast are slightly different than the rules in the southeast. Yeah. Actually, when we were starting to talk about what podcasts we wanted to record, um, I suggested this to Jonathan, and I said, well,

let's talk about all the different kinds of signals. And then when we got into, uh, the complexities of how the systems are triggered for railroad crossings, we realized we wouldn't be able to get that in as much detail as possible. But if you're interested in knowing more about that, please let us know, and you know, maybe we can

revisit that. But I've always been interested in the switching systems and how uh you know they they operate that because um, you know, I'm I'm kind of interested in trains anyway, but you know, the signals that say, okay, wait you can't come this way just yet. And how they shunt tracks from one, uh you know, from a train from one set of tracts to another set of tracks using those electrical systems. So if you if you're interested in doing that, please let us know and we'll

come back to trains in the future. Clearly, Chris needs to go see the film Unstoppable. That's the one with Denzel Washington and the train. That's the missile, the size of the Chrysler building. Stop it, it'll be awesome. Oh that's no train, that's a space station. See how many random quotes we can throw it? Yeah, I think you just mixed up those a little maybe to tad, I'm a little loopy today. Al right, guys, well they loopier

than normal. That wraps up this discussion on text UF. Please, if you are interested in giving us topics that sort of stuff, join one of our lovely social networks like on Facebook or Twitter, because more and more people are submitting that way and it's just getting easier to collect suggestions through those uh those means, so please use them absolutely, and Chris and I will talk to you again really soon.

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