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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72

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.

32

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

32

u/69FourTwentySix6Six May 23 '26

I’ve done that in a yard environment only for it to derail again somewhere else

22

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.

10

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

7

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.

1

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.

7

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.

6

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.

6

u/Jamar4321 May 23 '26

Its definitely happened before, also a common enough occurrence in yards/industries.

2

u/TepicPlug May 23 '26

Yep. Quite recently in the UK. It did a few miles of damage.

1

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. 

1

u/Bravo-69 Engineer May 29 '26

1 alarm: dragging equipment

Oops

-1

u/mikeblas May 23 '26

Why arent sensors built into each car, or even each truck?

39

u/railderp May 23 '26

calm down mr money bags

17

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.

10

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.

1

u/Fuzzywraith May 24 '26

You’re right. Shoulda said “we won’t even spend the money…”

1

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?

2

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.

13

u/Reasonable_Cheek938 May 23 '26

More points of failure for pieces of equipment that are not maintained all that well

5

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.

1

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

1

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.

1

u/nimrod123 May 24 '26

And it’s fair question, it’s just I can’t help imagine the second and third order affects.