2006 Q2 Wrong Side failures

[PJW]

Dorothy,

A thorough answer to a seemingly easy, but quite difficult, question. Seems a little long for 30 minutes but your exam technique may be to do so. There probably is a pass in there but the question hasn't been fully answered even though there are some important and relevant points in there.

First point is a suggestion; answer each question fully rather than split. Technique tends to mean the subject is repeated anyhow so context won't be lost. Not sure there are eight marks of consequences.

Good for picking up TPWS is not for stopping trains at red aspects. However, later on you discuss about overspeed mitigation and this should be mentioned at the same time. So, by definition, TPWS is not for SPAD mitigation. It is to remind an operator that an speed or movement authority is/is-to-be exceeded. Because of this and arguably, TPWS not energising is not a WSF per se, I agree, this was a bad example to use. TPWS would only activate the on-board equipment if a failure (operator error, signal reversion etc.) has/is taken/taking place. I would be interested to see other's views on this.

WSF2 - the failure described is generic. The WSF failure is a miscount out (so out==in when physically out!=in) so the section believes it is clear when it is occupied, i.e. more permissive. A miscount where the section shows occupied is a RSF. The early part of the answer discussed RSF whereas it shouldn't but improves further on. The "This is particularly..." paragraph isn't correct for a WSF question.

Suggestion for a WSF would be a relay sticking, incorrect indications etc. A more permissive indication to the train/operator than should be provided is the acid test.

People are very sensitive nowadays when calling things Wrong Side Failures.  A bit similar to the fact that many regard Test Logs as bad and therefore using as a metric to assess the status of a project pre-commissioning or as a surrogate to measure design quality; there is of course some correlation but it is indirect, certainly not a proportional relationship.
I am old school and therefore if a fault results in a reduction in the level of protection then I call it wrong-side.  I am perfectly comfortable therefore in saying that a couple of blown bulbs or a wire coming disconnected within a panel gives "a wrong-side indication failure"; the track shows to the signaller as clear even when the track itself is occupied and the interlocking is treating it as such. In other circumstances when perhaps there is a failure of the TDM bit and therefore a clear track actually displays as being occupied, the signaller could observe a signal at green reading over that section and must assume that has witnessed a Wrong-side failure although once the problem is understood it would be re-categorised as a Right-side indication failure.

Therefore my view is that a TPWS that is not active when it should be does constitute a WSF; it is not relevant that TPWS was never designed as a vital system. In fact WSF/RSF is too simplistic a distinction   nowadays; taking a holistic view of the railway system, just putting signals back to danger is not the end of it with signal engineer able to pat themselves on their back and think they have left the system in a safe state.  Somehow that train will have to be authorised to pass that signal and there are risks associated with that, in addition to the risks associated with fixing the fault.