Comment by lb1lf | Hacker News Reader

Comment by lb1lf | Hacker News Reader

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Just after two trains had crashed at Åsta in Norway back in 2000 or so, a journalist from the Norwegian Broadcasting Company managed to ask the accident site manager whether the trains had been on the same track when they collided.

Long, crushing silence, then. "Presumably, yes."

If I remember correctly, one of the key findings after the accident was that train controllers' only means of communicating with the trains they were supervising was to call the train drivers. On their personal cell phones. It was part of the procedure prior to starting a journey to call in to the central and have the controllers write down the phone number to be used to reach, say, the southbound from Trondheim.

Now we luckily have modern train management systems and GSM-R, but 19 people died at Åsta because the northbound driver seemingly forgot that there was a southbound train on incoming on the track he was going to use - and didn't pay attention to the signal telling him the track was occupied. Then, once the northbound train got going, train control took a couple of minutes to figure out what had happened and then also found out that he couldn't find the note with today's phone numbers.

Wow. That's kind of crazy. Seems like the main failure was the northbound running the signal, though. The lack of radio just means that they had no way to save the situation after the mistake happened.

Nowadays, the train controller can stop a train remotely even if unable to raise the train on the radio.

Still baffles me how packed the old system was with failure modes, though.

What system do they use for this? I’m not aware of any remote-stop functionality outside of driverless railways but that’s not to say it doesn’t exist.

I only know what i've read about it in the papers, but I think the concept was that the trains and track are fitted with instrumentation enabling the train controller to see in real time exactly what segment of track any train is on at the moment; he will then periodically authorize a train to occupy the X next segments. Presumably the system is interlocked so that it is impossible to authorize two trains to occupy the same segment at the same time.

If a train finds itself on a segment it has not been authorized for, it stops - regardless of what the driver thinks of the matter.

That system is track circuitry that uses relays to detect rolling stock when they short the two rails via their wheels. That exists widely, and it identifies that rolling stock is present in a track section. That same relay also locally (as in, on the ground at that location) triggers any signals to switch to red.

Controllers can’t then give authorisation to another train to enter that section, nor can they override any red signal. In cases where it applies, they also can’t remotely control track switches to enter this occupied section. However there’s nothing with that system that then controls the rolling stock itself, so a driver can still SPAD if they don’t see or ignore the red, and the remote network controller absolutely cannot stop a train that is hurtling towards an occupied section. That’s all on the driver in the cab.

Fun fact: track clips are used by track gangs to short these sections in lieu of a big axle sitting on it, which is one of the methods of providing site control to the gangs so trains don’t enter their worksite. It’s certainly not the only one, though.

I googled around a bit out of curiosity, and it appears the remote control is indirect - the train controller can override a green signal to red. (Presumably not the other way around!)

All trains have instrumentation which will cause them to stop if they pass a red signal.

The gritty details appear to be in the Togframføringsforskriften, however this has been repealed a couple of years ago, presumably to bring us in line with EU regulations - but I am too tired to try to figure this out tonight, though I have always been a sucker for figuring out how signalling systems work...

Yup, any controller can set a signal to red (that’s how we do track blocks, said clips are the backup to that because you always want the dude in the sky to know you’re there).

Not all trains have kit to stop a SPAD, unless you meant specifically in the instance of the operator involved in this incident. Some do, but it’s absolutely not universal around the world. For example, Automatic Train Protection (ATP) can do this, but it requires both a track-side magnet and the rolling stock to have the kit for it. We use that to trigger our driver vigilance system acknowledgement when approaching suburban passenger stations. Failure to acknowledge the vigilance prompt will throw the brake to emergency and stop the train.

That said, it’s absolutely not present out in the Wild West of freight (because maintaining that many ATP magnets is insanely prohibitive).

For information specific to Norway (in Norwegian) there is a lot here:

https://trv.banenor.no/wiki/Forside

https://www.jernbanekompetanse.no/wiki/Forside

This is a bafflingly casual regard to safety, with not even a token based system to grant access to a particular section of track. The problem that caused this accident was solved in the 1800’s.

Well, the train didn't have the (notional) token, so the signal was correctly at danger. Which is the 1800s solution to the problem (absolute block signaling). And in the 19th century it was also difficult to reach train drivers who passed signals at danger, due to a lack of radios etc., which did cause accidents when signals failed or drivers passed them at danger.

Box-to-train emergency communication was itself definitely a solved problem by the mid 20th century, though...

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