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Comment by secondcoming | Hacker News Reader

> Crashes would be avoided by having every train know about the train ahead and behind

Isn't this a block system?

> it is not allowed to slam the brakes on if there is a train right behind you

So if we have three trains in close succession and the first derails or loses power, the second is not allowed stop because there's a train behind it?

> Trains are usually 10's of minutes apart, or at least 1 minute apart even in urban subway systems.

At least on the London underground it isn't unheard of for the next train to be arriving in 1 minute. Most delays are caused by passengers, not infrastructure.

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The 1-minute (or less) headways on London Underground are precisely because of signal modernization over the past couple decades that has moved certain lines beyond purely fixed-block signaling.

AFAIK the underground is not beset with blockages caused by fallen trees and stalled automobiles.

It does have its fair share of 'people under a train' and people preventing doors from closing.

Which is why ATO (automatic train operation) is most often found in subways where the platforms can be equipped with gates to keep passengers out until a train has stopped safely. Suicide by train and level crossings are a nightmare in risk management for railway safety, hence also (new) high speed tracks are usually planned without any intersections with roads or paths, at respective additional costs.

Some lines on the London Underground do use ATO without platform barriers. The driver closes the doors, checks that the platform is clear, then starts the train. ATO takes over until the next station, where the driver watches to make sure there's nobody too close to the edge, ready to slam on the emergency brake.

> So if we have three trains in close succession and the first derails or loses power, the second is not allowed stop because there's a train behind it?

The second is allowed to follow the 'train ahead derailed' plan, which presumably will involve stopping at a rate that the third train can also achieve.

If comms is maintained during the event, new plans can also be made that are maybe better (eg. maybe try to brake harder than the guaranteed minimum braking)

Instead of a derailed train and a couple delayed trains you now have a derailed train and a couple of trains with flat wheels that also need clearing up (assuming they avoided slamming into each other)

Definitely not sold on the "let's chuck out the failsafe method of railwaying" idea, haha

Interesting. Never thought about that, but are you saying that emergency brake on train tears wheels so much that it's not able operate normally? Interesting learn.

(the whole thread started by overconfident guy with unrealistic ideas ended as very informative, so actually net plus, who would thought)

While it won't guarantee such level of destruction, emergency braking generally involves breaking beyond normal usability limits - including allowing for effective destruction of components in process

Aye as the sibling comment says it's not guaranteed to happen, I'm considering the worst case scenario outside of collision (needing to move trains that can no longer move themselves, needing to offload and transport stranded passengers, causing further delay, etc)

For what it's worth overconfident guy kicked off an interesting conversation!

It's also quite possible that I'm overcautious and the future will have trains within braking distance of each other and it turns out to be no big deal.

Thoroughly enjoyed thinking about the scenario in any case. Some proper Hacker News brain tickling in this thread :)

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