2004 Headway Calcs

[PJW]

Hello Peter,

Thank you for your reply.

I must say you have not lost form - your response is as quick as ever!

With regards to my question on 4 aspect signalling, one reason I see the merits of 4 aspect signalling around Station D is that the shorter sections between signals will enable greater throughput and better capacity optimisation especially with trains of different speeds, stopping and not stopping given that there is a permanent speed restriction of 40 km/h around Station D.

Regards

Alex

Indeed; the non-stop calculations are applicable for the section of the line where all trains are going at constant timetabled speed- not applicable to the station area.

You seem to have got different values for SBD at 100km/hr and 40km/hr than included in the Study pack Appendix W. There can be no other reason for this than arithmetical error (and having rechecked I don't think it is me!)

Whereas the first 4 columns of the table are perfectly self explanatory given your column headings, I think that the remainder needs considerably more explanation. The idea in the Study Pack was to give the numbers to give those working through it the confidence that they were getting the right numbers mathmatically, NOT to show how an answer to the exam should be presented- there are other examples provided for that.

You need to be clearer that the 120sec relates to the specification plus an allowance for contingency. You also need to justify WHY you are building in that level of over capacity. You are right to round down the headway distances and quote to a round 10m; the important thing is to keep a sense of perspectiveand to me 3999.60 is effectively 4000m for all practical purposes!

You certainly mustn't just quote DGR formula in column 7. Your heading does state certain assumptions but there is no expalnation how these factors influence headway, let alone what DGR is and why it is relevant. Further, the significance of what seems to be a random ratio between this unknown quantity and the SBD for determining the form of signalling being proposed is completely obscure.

The marks in this question are largely for demonstrating your understanding by giving a clear explanation- just calculating the numbers themselves won't give you much credit. You MUST concentrate your attention in being able to give that explanation and not rely on knowing formulae to plug numbers into- especialy those that you don't even quote. I think that you ought to have another go at producing an answer that would gain you more marks; you need to train yourself to produce on demand a clear explanation that doesn't consume too much time. There are various bits in the Study Pack that ought to help you construct that explanation and by getting practice in reproducing it ou should gradually be able to refine it; in a sense it is like the effort you made getting to a standard Control Table blank that suited you in mod3.

I haven't yet looked at the 2nd part in detail, but that actually seems rather better presented. I think a diagram would be a useful supplement in order to relate sections:a,b,c,....f to something and to clarify what you mean by "signal protecting platform" given that at this stage there are no signals on the layout- there is obviously an unstated assumption somewhere!