(27-03-2010, 11:41 AM)alexgoei Wrote: Hello Peter,
Sorry for not making the deadline of 26th March 2010.
Appended please find my workings.
I have some questions please:
1 While the calculations show that 3 aspect signalling can support the headway requirements, the model answer has 4 aspect signalling in the vicinity of Station D. How was this conclusion arrived at? I mean the calculations do not show 4 aspect is needed.
2 Single Line on the Branch - I do not see the need for stopping headway calculations on the Branch. Three aspect signalling can support the speed of 120 km/h.
Look forward to your reply
Thank you & Regards
No problem- it is just that quite a few people have expressed a theoretical interest in joining a virtual Study Group- what I am trying to establish is how many are actually going to participate in practice- I was working on the assumption that you be one of those who would.
Re your queries: one thing at a time; first the calculations to see what is the minimum level of signalling required to meet the headway requirement whilst satisfying braking constraints; then consider the particular layout to decide what signalling it is best to provide to respect the results of the calculations BUT ALSO take other factors into consideration!
I am not disagreeing with either of your two statements. However looking just at question 1 of the 2004 paper, this says;
Determine theoretically, either by calculation or graphically, appropriate signal spacings for the braking characteristics and the intensity of traffic on offer. All calculations and graphs must be shown.
It does not explicitly ask for stopping and non-stopping calculations to be performed for all parts of the layout shown, does it?
Interpret it as saying "Using your skill and judgement based upon experience and an understanding of the salient factors, decide what are the important headway constraints to satisfy when setting about signalling this particular layout. Concentrating on those factors that you consider key issues, [which may perhaps be:
a) platform reoccupation times at a through or terminal station,
or
b) following train capacity in the plain line sections,
or
c) a "bottleneck" constraint due to needing to operate traffic in either direction along a single line section or junction occupation times for a busy intersection of traffic flows]
determine what constraints these would impose on your choice of signal spacing to adopt when later placing signals on the actual layout diagram. Record the numerical values of thse constraints and explain their derivation.
Once we have got people happy with Q1 then we will consider Q2; you are right however that an initial assumption may need revisiting when other factors are taken into consideration
PJW