I know its an industry wide issue and Metro really suffers heavily with it. I'd be interested to hear from a Signallers perspective why its so common, how easy it is to do, what precautions can be taken and *deep breath* doyouthinkautomationsuchasARStechnology is the answer ?
I’m not a signaller. But I have spent some time on an operating floor.
Have you ever driven your own car to a place near to you home, but on a slightly different route? Say going to pick someone up or drop them off? And did you get distracted and then realise after passing the junction/turning that you had made a mistake and gone the wrong way?
With signallers, with a mainly clock face timetable, it’s very easy to run on ‘routine’. So if there is a train with a similar head code /train description ‘number’, it’s so easy just to set the “normal” route for that train. Remember, the only thing the signalling system tells the signaller is that (1) there is a train (indicated by the track circuits or axle counters) and the TD (train describer) showing the head code /train description ‘number’.
Of course, the signaller should have a schedule available to them. In the past this was a hard copy printed on paper. But these days, most signallers have access to a computer with an electronic version.
However, if the signaller is busy, then they will not always have time to cross check this for every train. Remember a signallers time is taken up with any telephone calls (public at a crossing, control, station staff, track workers wanting a line block, S&T trying to maintain or fix a part of the signalling system, other drivers or train crew…). Or talking to an adjacent signaller to pass on information.
The signalling equipment itself has no way to know which way the train should be going. It only checks that the route the signaller is trying to set is safe and allowed within the design.
Once the signaller routes the signal, the signalling system will once it has checked that it is safe, clear the signal to the appropriate aspect.
As said above ARS will set a route determined only by the information that has been put into the database schedule by a human. If ARS is in control, unless the signaller is monitoring it closely, the train driver is going to be the only person to spot the error…