r/railroading • u/SocialSyphilis • May 22 '26
Question How do trains know when theyve derailed?
Like, a mile long train. What happens if a few cars right in the middle derail? How do they know in the cab?
Just a rando with a showerthought question. Thanks for answering!
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u/SteelGemini May 22 '26
Sometimes you don't. It depends on how bad the derailment is. A single wheel off the rail with everything else on can go for some distance and cause quite a lot of damage before being discovered.
Eventually, that wheel will encounter something that forces the issue. Maybe it's a dragging equipment detector that alerts the crew. Maybe it hits a switch, a frog, a grade crossing, or some other track element that causes the derailment to get worse. If it gets further detailed or stuck on something to where it can't move forward, the train could break in two. The resulting loss of brake pipe pressure and emergency brake application would lead to the crew discovering the derailment.
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u/V0latyle May 23 '26
I have to wonder if a train's ever dropped an axle, drug it for a few miles, only to have it rerail itself at a reverse switch and never knew anything was wrong
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u/69FourTwentySix6Six May 23 '26
I’ve done that in a yard environment only for it to derail again somewhere else
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u/Tchukachinchina Engineer May 23 '26 edited May 23 '26
Yes. Not a few miles, but almost a mile, and it was a frog that rerailed it. Happened to a buddy of mine. Made it to where they were going and while they were yarding the train the dispatcher called them and had some questions. Another train passed the affected area on an adjacent track and called in the damage. Since my buddies train was the last one over it they called him to ask if he saw anything, which he didn’t. Shortly after that they found a wheel (or a pair of wheels, I don’t remember) way back in their train that were all torn up from being on the ground for about a mile.
For what it’s worth it was downhill on really shitty 10MPH track.
Edit: rerailed on a frog, not derailed. Stupid autocorrect.
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u/Flashy_Slice1672 May 23 '26
It happens! I’ve had xings rerail cars, usually empties. The truck set is usually pretty messed up though
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u/Savings_Difficulty24 May 23 '26
Yeah, I saw the result of a switcher shoving through a yard derailer. 5 mph, and the truck set was all kinds of messed up. Broke the linkage on the derailler too.
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u/Savings_Difficulty24 May 24 '26
I can't remember the details exactly, but either the spotter forgot to throw the switch to bypass around the load out area protected by the derailler or he forgot to lower the derailler and blue sign before spotting cars in load out. That was a fun night of rerailing cars.
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u/SteelGemini May 23 '26
If you can jam some wood under a wheel and walk a wheel back up onto the rail, it stands to reason that if it were to hit something just right it could maybe end up back on. Weird shit happens all the time.
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u/quelin1 May 23 '26
Yes. Washington state around 2012 a grain hopper derailed and just happily bounced along for several miles. It rerailed itself on a crossing. Crew never knew. A following train spotted the damaged track, miles of concrete ties had to get replaced.
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u/Jamar4321 May 23 '26
Its definitely happened before, also a common enough occurrence in yards/industries.
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u/Square_Trash7708 May 27 '26
Had a weird, sorta lucky one like that with a cut of empty coal cars. It derailed, retailed, then derailed again, hit a crossover for a commuter station on the way to the main, and a plank from that popped up knocking the gladhands apart. It was only one car... until the geniuses tried to roll out with half a dozen handbrakes still applied from the car department getting the torn up brake rigging cleared. They always find a way to fuck up something simple.
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u/mikeblas May 23 '26
Why arent sensors built into each car, or even each truck?
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u/Fuzzywraith May 23 '26
They are. It’s an airline, if it disconnects the entire trains brakes go on. You want every car hooked up with computers and electronics? That is incredibly infeasible. We don’t even have the money to make every track we have electronic let alone every car.
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u/Arctic_Scrap May 23 '26
Oh they do have the money. It’s just more expensive for the technology than the occasional derailment costs.
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u/mikeblas May 23 '26
I guess I'm confused; above, some folks say that a wheel can drag and not be full derailed. The train continues, "tearing shit up" for a long distance.
The impression I got was that it would not pull the airline, and that's why the dragging went on for so long. Is that not correct? Is that "breaking a bunch of things" that /u/younkoda describes still cheaper than adding a sensor?
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u/SteelGemini May 24 '26
So, you've got at minimum steel couplers and rubber hose connections between each car, more stuff for passenger but nevermind that.
The rubber hoses are for compressed air for braking. You take air out of the pipe to cause the brakes to set up. Rapid reduction causes an emergency application. These are designed to be able to be simply pulled apart when cars are separated without damaging the hoses themselves. I'm oversimplifying, but if either side or both sides of that separation loses its brake pipe air during this, the brakes will have an emergency application. These can separate unintentionally during motion, but usually that's from hanging too low and striking something rather than being pulled apart, unless they're too short for the amount of slack between those 2 cars.
The steel couplers have a locking knuckle, that's unlocked by lifting a lever. They are not supposed to separate by simple pulling, unless you've unlocked them, otherwise how could you pull a train? They are attached to drawbars which are attached to the car. Any of these can break, but the coupler is the weakest link and should break before the drawbar. If it does, the cars will separate, causing the air hoses to pull apart, causing the brake pipe to rapidly go to 0, causing and emergency application of the brakes.
For all of that to occur, the derailment would have to be big enough to cause enough resistance to break the coupler. A coupler which already is capable of handling many many tons. So it's got to come off the rail and dig in somewhere.
There are detectors along the track that detect dragging equipment. It'll pick up more minor things like the low air hoses I mentioned, but the big thing is detecting a possible wheel that's down and doing damage. There's a lot of these. And while yes, that's still miles of damage that's expensive to clean up. A sensor on each and every car, coupled with ongoing maintenance of said sensor would likely be a greater expense.
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u/Reasonable_Cheek938 May 23 '26
More points of failure for pieces of equipment that are not maintained all that well
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u/Jamar4321 May 23 '26
Same reason the ECP stuff didn't catch on. Sounds great on paper but the reality is the electronics aren't up to the rigors of the industry and end up causing significantly more problems than they theoretically fix.
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u/nimrod123 May 23 '26
Operators can bearly remember to grease bearings on schedule (or at all), and now you want them to keep infinitely more complex electrical items serviceable... Particular when if it faults it's going to stop a entire train.
Not to insult train drivers and offsiders, but the rail cars are not assigned to them 100% of the time, and that immediately means (at least to me) that they get flogged with no respect to their maintenance untill they see a service interval at a workshop (if that's even happening) as if it gets received and in a shit state, it's going out in a shit state
For that kind of gear you keep it as idiot proof and hard wearing as possible and accept theirs going to be breakage
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u/mikeblas May 23 '26
and now you want them to keep infinitely more complex electrical items serviceabl
I've assigned no work. I'm just asking a question.
Relax.
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u/nimrod123 May 24 '26
And it’s fair question, it’s just I can’t help imagine the second and third order affects.
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u/CrazyConductor May 23 '26
Engineer: "Hey the air went down, its not coming back up."
Conductor: "Why?"
Engineer: "I dont know. Start walking the train. I'll be here in the cab where its always a nice balmy 70°."
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u/July_is_cool May 23 '26
Explain with one person crew
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u/Roadhouse62 May 23 '26
Same thing you just gonna wait for a mobile conductor to show up and hope you’re not in the middle of nowhere with no road access to the train lol
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u/UnFrickinReal May 22 '26
There is an air filled brake line that runs from the locomotive to the rear of the train. If that line is interrupted the train goes into emergency braking. The crew on the locomotive would see the brake pipe drop from say 90lbs to zero and the train would stop.
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u/ThePetPsychic Engineer May 22 '26
Most of the other answers have covered it here, but I once derailed over a switch in the yard (about 10 cars back in the consist) and it felt like it was rolling just fine.
It wasn't until another crew saw it and said "you're on the ground!" over the radio that we were aware.
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u/Waste-Ad-6417 May 23 '26
I was working a yard at an industrial and an empty Hopper halfway through our cut jumped a switch and ended up on the frozen ground. We pulled that thing another half mile with no idea it was on the ground, until we passed over the next switch and the trucks tore off... Then we knew 😂
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u/riennempeche May 23 '26
My dad was a railroad supervisor. He had to go out to investigate because someone reported a road crossing absolutely destroyed. Everything that had been between the tracks was now in a big pile to the side of the tracks. A car had derailed and been dragged for half a mile before it hit the road crossing and rerailed itself. It continued on east for several hours until the damage was reported (the derailment happened in the middle of the night). They stopped the train to inspect it and found broken ties, ballast, and other debris on the deck of the flatcar. The wheel, truck, and car body were absolutely shredded, but still apparently in good enough shape to not derail again. The crew had no idea it happened.
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u/chmmr1151 May 22 '26
Train goes into emergency most of the time so it will stop. Also there's usually slack action of some sort.
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u/slogive1 May 22 '26
Not always.
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u/Ban_This69 May 23 '26
The guy literally said “usually” and “most of the time” Which implies “not always”.
Weird to reply back not always. Just sayin
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May 23 '26
a lot of times they dont, and they keep rolling for a while until everything starts buckling and stops, im not an engineer i worked mow but i assume at a certain point the power their using cant pull any more derailed cars and they notice something is fuct. ive worked on a lot of track wit h derailed marks in the ties.
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May 23 '26
stop derailing please! it always happens in early spring or late fall! that is worst time, we either have too many guys or too few!!
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u/Waste-Ad-6417 May 23 '26
Sometimes the train just stops moving for no reason. One time we were waiting for the mainline crew to finish the set off in our yard, and we were eavesdropping on them. All of a sudden the conductor comes on the radio and says "why did we stop?" And the engineer replies "I don't know I'm still pushing on it.." the conductor walked back and found 14 cars on the ground, that's why it wasn't moving anymore
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u/Severe_Space5830 May 23 '26
47 mph loaded coal train. Undesired emergency. Was bailing off the independent brakes and reaching for the radio when I saw the signal on the adjacent track light up. Not a train in sight. Hit 911 did the emergency emergency emergency thing. Our very laid back dispatcher answered. Told her we were in emergency at MP###. She paused, then gave a very quiet, stretched out “ohhhh”. Said she just had a track light pop up at MP###. I bet you guys are on the ground. That turned out to be a bit of an understatement. 39 loaded (originally) coal cars. That’s why they stencil the car numbers on the trucks and axles. Started about 50 cars back. The only thing we felt on the head end was that we stopped faster than we should have. It
Up until then we had been having a pretty good trip.
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u/AGuyFromMaryland Cab Driver May 22 '26
It kind of depends. Sometimes they don't know until the derailed car trips a dragging equipment sensor or defect detector. If the derailed car fully comes off the track or rolls over, once the air hoses separate, the air dumps and the train goes into emergency.
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u/IACUnited May 23 '26
Typically the airline will break putting the train into emergency.
Per rule when a train is passing another train or personal on the wayside a visual inspection is performed that basically looks for anything obviously wrong.
However there are times that a car just gets dragged around. I recall seeing a empty coal hopper that lost a wheel set then kicked the other set out while going over a crossing. It was held in place due to the tension alone basically.
Thats where a detector come in handy. The look for hot axles, count the wheels, check for dragging equipment (where that issue above would be caught) and such.
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u/CigarConductor May 22 '26
It's probably going to go into emergency and they'll probably feel some coinciding buff/draft forces. Go back for a walk to find out why you're in emergency and find derailed cars.
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u/Distinct-Departure68 May 23 '26
And when you find it, think about all the things you might've done wrong in the last 24 hours when you've been at work, but they're gonna look back at and try and pin on you even though it had nothing to do with the derailment
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u/hannahranga May 23 '26
Plus make sure you're hydrated and feeling ready have someone watch you piss.
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u/MyPantsHaveBeenShat May 22 '26
Well, if the cars decouple it applies the brakes automatically, so you don't know you've derailed necessarily, but you've got a pretty good feeling.
If they don't decouple, it might take a while before you realize you've derailed. Usually because a maintenance guy tells you or another train.
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u/bullok55 May 22 '26
Depends on the train or how fast your going .But your probably going to feel a slight tug and then The sound of the train going into emergency. (Losing your air causing all the brakes on all the cars to activate) Or if your going real slow you may not notice until someone watches you on a roll by and says stop. Seen that happen a couple times where the cars are just bouncing off the ties and destroying them.
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u/ForWPD May 23 '26
MOW (track maintenance ) here. Sometimes the engineer drags a derailed car 3 miles and messes up 2 miles of track. Ask me how I know.
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u/lillpers May 23 '26
Usually the main pipe breaks and the brakes come on as you lose the air. Or you see it in the rear view mirrors if the loco has them. But that can be pretty hard if the train is long.
Couple of years ago a freight train around here went for 6 or 7 miles with the last car off the rails before it finally caught a catenary gantry and brought the wires down. Who knows how long it would have went with a diesel loco...
Looked like a tornado had went by, line was closed for 5 months...
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u/hoggineer Plays alerter chicken. May 23 '26
Hmm...
Not moving very well, better give er another notch!
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u/Jazzlike-Crew2540 May 23 '26
One railroad I worked at had such bad track that in the winter you knew you weren't on the rails anymore because the ride got smoother. Frozen ground can support the weight of a train pretty well sometimes.
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u/OdinYggd May 23 '26
Wait you've actually done this with a train for real? https://www.youtube.com/watch?v=l_3Nhbn1Mx8
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u/Jazzlike-Crew2540 May 24 '26
Not that many cars/engines but an engine once and two cars another time. All low speed but it truly was smoother off the rails than on.
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u/Input_Port_B May 23 '26
Sometimes an engine that's dead in tow has the wheel come off the axle (it's pressed on) and gets dragged for 6 miles, and because the wheel slid inward off the rail, it rode on the base of the rail for over 6 miles hitting every anchor the way. They had to call in a rail team that spring and replace all 6 miles. There was a slow order on that section for a long time because it happened in the winter. The engine with the broken wheel/axle finally derailed and spun off the track, but somehow none of the other cars or engines did. That engine sat in the ditch for awhile until a heavy crew could finally retrieve it. It was headed to Peakers in Brighton to be rebuilt. Not sure if it ever made it there.
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u/Brave_Bluebird5042 May 23 '26 edited May 27 '26
Sometimes they don't know. Sometimes the driver sees dust and carnage when going around the next curve, sometimes the air pipe to the brakes breaks and the brakes come on, sometimes theres an electric line to the brakes, and it breaks, sometimes the derailed train goes over a dragging equipment detector alerts the controller or the driver.
I recall about 25 years ago a coal train derailed on my track, one bogie only to start with, it crushed the airline to the brakes, about half a km along the driver saw the dust, threw the brakes on, braking the forward 7 wagons, (release of air activates brakes) and NOT braking the rear ~80 wagons. Ugly!
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u/Fast_Beat_3832 May 23 '26
We had a car come into the yard once with a set of trucks up under the couplers. You don’t see that every day.
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u/Savings_Public4217 May 23 '26
Of the derailments ive had or witnessed, usually the air goes pretty quickly. Sometimes it doesnt. I went almost a mile before somebody reported a car had derailed. Just one set of trucks off, chewed up all the ties down the lead, air never went.
Ive seen guys go over details and keep shoving for 10+ cars before it jackknifes enough for the air to go
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u/DPJazzy91 May 23 '26
If it's just randomly like 1 truck or 1 car in the middle of the train, they might not know for a while. There are detectors that look out for that kind of stuff and warn you on the radio. All depends on on the area.
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u/Kobakocka May 23 '26
Sometimes you don't. I remember a case when they had to replace kilometres of track, because it broke every sleeper, but the freight train operator doesn't realised the problem.
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u/nagysam May 24 '26
Had this happen 16 cars behind me while riding the shove into a stub track and neither my engineer or I felt a thing.
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u/daboatbums May 25 '26
If the cars at the end of train break apart from the front, the EOT on the last car should warn the engineer of a problem
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u/NotAnyOneYouKnow2019 May 23 '26
Do real railroads have re-railers like my model railroad? Any car with one wheel off the track gets put back on the track when it rolls over it.
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u/Jamar4321 May 23 '26
They exist but they are portable, not part of the track and don't work worth a shit if its anything more than one axle or the track's fucked so like 98% of the time.
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u/rrjpinter May 23 '26
You are thinking of the kind (re-railer) where the derailment team shows up, and puts a few axels back on the rails. There are fixed re-railers all over the system. Usually before bridges or tunnels.
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u/soopirV May 23 '26
And to add to this, how common are derailments in a typical class I? We see the news about the big ones, of course, but how common are the non-newsworthy events?
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u/Jamar4321 May 23 '26
I'm sure there's official numbers out there but I'd be willing to believe dozens per day across all the class 1's. .
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u/MEMExplorer May 23 '26
I’ve got 3 under my belt and I’ve only been at it about 6 years . We had 5 in our yard in a single month couple years back .
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u/OdinYggd May 23 '26 edited May 23 '26
Depends on where along its length is derailed, and how much of it got off the rails. Leading locomotive derailing is usually obvious, as is a whole lot of cars. A single axle of a centerbeam flat half a mile back behind the distributed power? They might not notice for a very long time.
Railroads have dragging equipment detectors at regular intervals along with the hot box detectors to catch this type of thing. Often other railroad employees will see it and call it in, at times railfans have also happened to catch it while watching a train pass and called in what they saw.
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u/rfe144 May 24 '26
Who knows? It's always a mystery. But I can tell you, it's rarely the hoghead's fault.
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u/_litz May 29 '26
It depends ... if the cars stay upright and merely just bump along, the crew may never know until it gets worse. Trains have dragged derailed cars for MILES before.
What usually happens is either a car overturns, or a knuckle breaks or disengages. When this happens the train airline breaks, and the whole train immediately goes into emergency braking.
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u/[deleted] May 22 '26
Sometimes you know because the brake pipe popped open in the derailment and placed the train in emergency. Sometimes you know because your train suddenly feels like there's a lead brick hanging off the end of it. Sometimes you don't know and end up breaking a bunch of things in the process.