I've received some additional information from a friend regarding the collision in Germany
The section of track is equipped with track circuit(s) to indicate occupancy to the dispatcher. The line is not equipped with signals to communicate conditions of occupancy to following or opposing trains once in the block, given that this is essentially absolute block, where use is restricted to one train at a time.
On this day, the section of track between stations had (a) track circuit(s) down continuously. This prevented the dispatcher from displaying the signals authorizing entry into the block normally.
After determining that the block was indeed clear, established operating procedures allowed (in Germany, as they do in the United States and elsewere), the dispatcher to authorize trains to override the PZB and pass the signal displaying stop, enter the block, and then accelerate to normal speed.
In these circumstances, the vital process then reverts to the train dispatcher's memory, and/or the correct entry on his/her record of train movements, or the information from some other party observing a train clearing the block.
The separation between office and field had disappeared.
The westbound train was then mistakenly authorized to enter the block with the eastbound train already in the block after having likewise received authorization. The "lap" has been established
So... occupancy was being registered in the field, but that vital process lacked its vital complement—a means of communicating the information to the trains operating in the field that would have required a reduction in speed, a restriction to the operating authority.
Automatic signals driven by track conditions are that vital means of communication. The failure of the track circuit, indicating occupancy, would have been translated into a signal requiring a sharp reduction in the permissable operating speed of the train.
Nobody was daydreaming, distracted, losing situational awareness. If this is indeed what occurred, then the dispatcher made a human mistake while faithfully attempting to meet his/her responsibilities. Those who designed the system made the equally human mistake of not accounting for human error when a fault in the machinery occurs.
Tragedy. No other way to describe this.
February 12, 2016
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