(01-10-2009, 09:13 PM)oxfordjack Wrote: Hello,
I would like to ask the following few questions:
1) if the lnterlocking system is degraded, what system may be put in place to maintain operation of railway.
(my query: Is it maintained by manual?)
1) Yes some form of train service can often be provided at an accceptable level of risk by pure procedural means such as authorising past signals at danger. However the signaller can do this more readily if can tell all points are detected in correct lie and are locked; otherwise needs to get someone out on site to operate points to correct position and clip an scotch them and give assurance that correctly set.
This may be broadly OK if a one-off failure but not tenable if failure affects a larger area of equipment. Perhaps could put in some form of ticket working with people trackside to check that a train has left a certain portion of line complete before another train is authorised into that section.
Graceful degradation is important.
Sometimes some secondary signalling system is installed purely to work in failure situations; probably only suitable for low speed, low density of traffic but at least providing means of keeping traffic running with some level of interlocking. One example is the POSA aspect- proving "locked wheel path" from signal to signal; no overlap, no flank, no train detection.
A track circuit railway may be given an overlay of a few long axle counter train detection systems as a back up. Conversely a railway that uses transmission based signalling with trains reporting their own position may also be provided with axle counter train detection as a form of back up perhaps fo the scenario of a non-communicating train.
This is a whole subject by itself- not a yes / no answer!
Quote:2) Explain some ways in which a lineside signalling system without automatic train protection can contribute to the prevention of derailment.
(my answer:
a: Can we add more signal lights avoiding from high speed.........
another I do not know
2) Again not a simple question to answer briefly. To answer this you would need to think what would be the various causes of such a derailment and how they could be mitigated. Derailment could be at points set incorrectly, following a SPAD, due to excess speed etc etc
So in scenarios where a signal is prone to SPAD then improving conspicuity, sighting distance would help and indeed adding a banner could be useful reduce the chances of it occuring. The design of the track layout can also influence; if the signal is further away from the hazard it protects then the consequences of the SPAD may be reduced. I think flank protection would also feature in the answer.
If necessary I think I could find enough to write to earn the marks for at least 15mins, though if it were a full 30mins IRSE question then I think I'd chose a different question as I think I'd be struggling to find enough non-repetitive material to earn all my marks
Quote:3) how ATP prevent derailment?
(My anwer:
a) Given Target speed can prevent overrun.
.........
3) The question said HOW. Your answwer just made a bland statement and did not even attempt to explain how.
Similar to Q2- you need to consider the various risk scenarios and how ATP could mitigate. This will depend whether the ATP achieves full continuous speed supervision, is only effective after a signal has been SPADed or lies somewhere in between. This is why you need to state you context and assumptions.
The answers you have given in each case are just a few words; this isn't what is needed in the IRSE exam. The questions should be prompting you to construct an arguement that demonstrates that you understand what the problem is and come up with a whole range of suggestions that address each of the various elements for particular scenario examples that you describe. So whereas what you have written isn't wrong, it is "just the tip of the iceberg"
PJW