Comment by 1718627440

> But aren't there additional systems that can detect that a block is obstructed (e.g. also by left behind carriages that got disconnected) like the electrical track circuit (Gleisstromkreis)?

That's not an additional system, that is the PZB (or here ASFA).

> Or wouldn't that have helped because we're back again to the issue that with the downgrade from LZB to PZB we lost the virtual blocks, and both trains are now occupying the same, longer, non-virtual block?

Yes.

> But they have no indication that there is a second train (Iryo) in front, occupying the same block.

We don't know what they missed, and speculating on that is quite pointless, if we want to have that discussion, we need to wait for the post mortem, this is what such a report exists for. We only know THAT they missed something. That they missed that the first train was in that block too, is one option. It could also be, that it was not clear which signals are virtual or that there was a communication mismatch between different dispatchers or that there was a bug in the automatic train identification system or that an automatic system did call for that procedure. All of these already do occur in railway accidents, they are not really speculative. The last one is what happened in 2002 in the exact same situation: the computer automatically ordered the second to full speed and the first to stop. There could also be some other issue, that I can't think of right now. Most likely it's more than one error, because people still do pay attention.

> Hence, I assume, the protocol to resume operations with drive by sight after a LZB failure (which seems to have been ignored in this case)

I don't actually know what the protocol in Spain is. In Germany it is like that now, but only due to the 2002 near-accident. Before that it was ambiguous. If you are a dispatcher you don't only get taught a bunch of rules. You get taught the primary constraints and then you are able to construct the rules from first principles. However under pressure it's likely to forget something vital, so there are still rules that you are supposed to follow. But no ruleset will be ever complete, that's why you don't only follow rules.

> But why not also have the protocol demand that operations are resumed front-to-back in that situation?

That wouldn't solve anything. Drive by sight is safe in that situation, driving faster is not. If you start front-to-back you can still have collisions, but you just waste time. There is also not necessarily no physical block between trains, so it could be safer to start a later train. Also are you sure you are able to correctly assess the positions and order of the train? You are supposed to, but I mean that obviously failed here. Just drive by sight.