What actually was the reason that caused the rail crash at Bad Aibling in Bavaria on Tuesday, February 9?
On Saturday, February 20 it was announced that the crash was the result of human error: a signal controller is alledged to have given a green aspect to one train when she/he should have stopped the train at red on a track-side signal.
Is that possible?
On all modern trains, driver-cabs are fitted with a device that informs them of the aspect of track signals in her/his section of track. And the train brakes automatically. Irish Rail calls this system CAWS, Continuous Automatic Warning System.
How was it possible for the train controller to have given two green aspects at the same time on a single running section of track?
When a train goes through a red aspect, alarm bells ring in a signal box/control room. When signals contradict one another it would make sense that all hell would break out in the control room.
And one of the drivers would have noticed that something unusual was happening, in which case he would automatically have phoned control. The driver(s) would be familiar with that section of track and the running order on that section, so the slightest change of what's 'usual' would have caused concern. The idea that both trains were travelling at the maximum speed of 100km/h only adds to the mystery of what happend on the morning of Tuesday, February 9 at Bad Aibling.
With great effort and planning it might be possible for a driver to override a signal safety device but for a signal controller to override the system would appear to be impossible.
Looking at the incident from a distance, it appears that the reason for the crash that has been made public is implausible.
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