Design fault for near miss
I read the article on the Norfolk level crossing near miss ( RAIL 921) and felt concerned that the root cause of the incident had not been fully understood, and that with the actions taken there remains a likelihood of repeat incidents and a risk to life.
In this case, it looks as if the root cause was the gate logic design and not the condition of the track.
I realise that the article was only a brief description and that more details may have made things clearer, but it looks to me as if the design for the crossing control is not fail safe.
True, the actions recommended may well reduce the incident rate, but they will not eliminate it. And they add even more work to already complicated planning processes.
I deduce from the article that the crossing controls are activated when an approaching train makes the approach track circuit. But if this indication is lost, then the gates appear to open to road traffic.
This logic is not safe. At the first indication from the track circuit, the gate logic should lock in until released by the safe passage of the train, not by the clearing of the approach track circuit. That way, any loss of the approach track circuit would not allow the gates to open too soon. It would be fail safe.
The indication of safe passage of the train should be by the occupation of the track circuit beyond the gates or some other suitable indication. Or has this already been done on more recent installations, but not retrofitted here as indicated in the final recommendation?
Forgive me for wasting time if I am wrong. But if I am correct, then it worries me that an investigation can miss out on a full understanding of the system and possible failure modes and fail to recommend essential design changes.
Having worked on safety systems within the chemical industry for many years, I have witnessed several times flawed conclusions from a lack of detailed understanding leading to the wrong actions being put in place. Fortunately, they were mostly in the design stage and could be corrected before installation began.
Tony Brookes, Cheshire