2008 Module 2 Layout Calculation Attempt

[PJW]

Certainly you could
a) work out the headway achieved at minimum spacing of 3 aspects; if good enought then that is your answer, if not
b) work out the headway achieved at minimum spacing of 4 aspects.

No need to mention DGR at all.

Sir,

I have one doubt, in your review..
Once he calculated the Headway (Distance & Time)using 3 aspect & 4 aspect, he could have come the conclusion which aspect signalling meets the headway requirements , then once again do we need to Appy DGR method and show the significance of Ratio "N" in selecting aspects.

Thanks
Dev

You then quote the DGR formula. You do need an annotated diagram to explain that derivation. You also need to explain why S = 38.8 x 10.

Similarly just stating that 1.5<DGR<2 therefore need 4 aspects does not demonstrate understanding. You need to say that it is not possible to get two minimum signal spacings of 1975m within the maximum spacing of 3908m needed to achieve the headway requirement. Therefore 3 aspects is not an option, so have to select 4 aspects.

HOWEVER, do read the question. You were asked to calculate the headway at minimum signal spacing, not at this time asked to determine what signalling type to use on your layout (although indeed you will need to determine that sometime before starting it).
So what you should have done was calculate what headway would be with 3 aspects at 1975m and give the answer, also pointing out that this does not achieve the 2 minute headway requested so therefore for your layout you will need to use 4 aspects. However placing 4 aspects at their minimum signal spacing would be excessive and therefore you will calculate the maximum spacing of the 4 aspects that would just achieve the headway specification.